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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Carburetor Shootout /cgi-bin/YaBB.pl?num=1585461605 Message started by DragBikeMike on 03/28/20 at 23:00:05 |
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Title: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:00:05 Carb Comparison – Installation & Performance This is a comparison test of four different carburetors. The contenders are the stock Mikuni BS40, the Mikuni VM38, the Keihin PWK38, and the S&S Super-E. The six categories for the comparison are installation, tuning, drivability, acceleration, fuel economy and maintenance. I assigned a number from 1 to 4 for each category, 1 being lousy and 4 representing superb. A perfect score is 24 and the worst possible score is 6. Installation: Ease of installation. Is it plug & play, or does it require extensive fabrication/modification? Tuning: Is it close out of the box or does it require modifications and/or hours of test & tune to get it dialed in? Are tuning parts (jets, needles, etc.) readily available? Drivability: Throttle response, smoothness, power delivery, idle, starting, afterfire Acceleration: 2nd gear time from 4K to 7K Fuel Economy: How many miles per gallon can you ride under normal riding conditions? Maintenance: How hard is it to work on? Is it easy to change jets? Is it easy to remove, replace, adjust? All four carburetors were installed on my modified 2016 LS650. The modifications include ported and flow tested cylinder head, Web 340b camshaft, RD valve springs & titanium retainers, three-inch flywheel, Mac 1.79” head pipe with modified muffler, hi-flow airbox with K&N filter, 10:1 compression ratio (Wiseco 94mm piston), ignition timing retarded 2°. Each carburetor was tested with the same engine setup, no changes were made to ignition or cam timing, intake or exhaust length, etc. Gearing and tires were stock for all testing. In other words, it was a level playing field. Install the carburetor, dial in the jetting, test & evaluate. Jetting was dialed in using an AEM Wide Band Air Fuel Ratio Meter, timed acceleration, and spark plug readings. Air/Fuel ratios of 12.0:1 to 12.5:1 consistently correlated with the fastest acceleration. Air flow measurements are for reference only, they weren’t used as a test criterion. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:01:20 The Contenders. Top left Mikuni VM, top right Keihin PWK, bottom left S&S Super E, bottom right Mikuni BS40. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:05:16 Mikuni BS40 - Stock Carburetor The Mikuni BS40 is a constant velocity carburetor. It utilizes a transient enrichment valve (TEV) to help mitigate afterfire (the big KABOOM when you decelerate). There is no accelerator pump. The BS40 has the smallest venturi, so it flows the least volume of air at WOT. It flowed 159 cfm @ 15” H2O. Installation 4: It’s already installed, no cable issues, fuel hose is correct, no special manifold or air filter. Tuning 2: Tuning the stock carburetor for a high output engine was not as easy as I thought it would be. It ran well at idle and part throttle but had a nasty tendency to go dangerously lean at high speed (around ¾ throttle). At WOT, it would return to a safe air/fuel ratio. It needed a compound needle. Aside from main jets and pilot jets, there just isn’t much available for tuning the BS40. Different size needle jets and jet needles are unobtanium. The 5C16 needle for the early model LS650 incorporates three grooves for the clip instead of a single groove and provides a little more flexibility. I eventually dialed it in by sanding a second taper at the end of the needle. The compound taper on the needle combined with a 205 main jet got things just right. Final jetting for this engine setup was: Main Jet #205, Pilot Jet #52.5, Needle Jet #X-7, Jet-Needle #5C16 with custom compound taper (clip in mid groove, no spacer or washer), Pilot Air Jet “1” #45, Pilot Air Jet “2” #230, Main Air Bleed stock (fixed .024”), Float Level 28mm, Idle Mix Screw 1.5 turns, Slide one extra air hole .107” diameter (#37 drill). Drivability 4: It is an excellent carburetor for a daily driver. Starts easy, almost always on the first crank. Quick warmup. Great throttle response. No hesitation. Super-smooth cruising. Occasional afterfire on deceleration. Acceleration 1: It was the slowest in the acceleration category with a 4K to 7K time of 3.30 seconds. Fuel Economy 2: Fuel economy, 56.6 mpg. It’s a compromise. To get the stock carb to deliver enough fuel at WOT I had to sacrifice some mid-range economy. Maintenance 2: Maintenance is not the easiest due to the size and complexity of the carb. Compared to the other three carbs, it’s harder to remove, harder to clean, harder to adjust, and easier to screw up. Total score for the Stocker is 15. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:06:27 Stock Mikuni BS40 Points of Interest Although the stock carburetor butterfly is 40mm, the oval venturi only has a cross section equivalent to a 35.4mm hole. This accounts for the lower air flow (159 cfm), which probably accounts for the slower WOT acceleration. The fixed main air bleed (shown in the lower right corner of the picture) is .024”. It’s another feature that limits tuning, but I didn’t need to mess with it to get the carb to work well. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:07:15 On the left is the late model 5C39 needle. On the right, you see the early model 5C16 needle. The 5C16 is a genuine Suzuki part that I purchased from Babbitts Suzuki Parts House. It’s for the early model (1985-95) LS650 (part number 13383-24B40). The 5C16 is a nice addition to your tuning capabilities, but not a panacea. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:07:54 This is a sketch of the modified 5C16 jet-needle. You can do the same modification to the 5C39 needle, but I wouldn’t do it unless you are using it on a souped-up engine. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:08:37 This shows the 3rd hole in the slide. It’s .107” diameter (#37). IMO, it helps a bit with response but can also aggravate afterfire. With the extra hole, the slide lifts faster, but it drops faster too. See those little screws in there? They can be tricky. A magnetized screwdriver is a must. If you install the retainer plate upside down it partially obstructs the air holes. It’s also easy to pinch the rubber diaphragm or install it in the wrong orientation. You must be careful. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:09:38 Here’s what it looks like from the bottom of the slide. The new hole must line up exactly with the notch in the small plate that captures the jet-needle. The black stuff on the outside of the slide is a special dry lubricant, another area where you must be careful. It’s easy to screw up. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:10:13 There is no plug for access to the main jet. It would be a nice feature, especially if you are running the stock battery box. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:10:48 The innards of the stock carb are typical. Float, needle & seat, pilot jet, main jet, etc. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:11:26 The large #230 air jet “2” (lower left in picture) is easy to mix up with the main jet. The #230 belongs up here in the top of the carb, not in the float bowl. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:12:06 The plug over the idle mixture screw has to be removed (red arrow shows screw, plug removed). The TEV valve adds complexity but helps with the dreaded afterfire (KABOOM!). |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:12:46 More TEV parts equals more complexity, but I think it’s a good feature. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:13:30 Not a lot of room to get the carb off and on, and the float bowl is tough to remove. This is one of the reasons I dumped my stock battery and battery box. The VM & PWK carbs do not have a butterfly valve so their float bowls are situated closer to the cylinder, and easily clear the stock battery box. The S&S carb won’t even fit unless the stock battery box is removed. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:14:05 This should give you a feel for how much additional room you have with a Sportster battery installed. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:14:52 Getting to the slide assembly requires a bit of work too. It’s either pull the fuel tank or pull the carb. Removing and reinstalling the stock carburetor is arduous if the stock battery box is in the way. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:17:34 Mikuni VM38. The Mikuni VM38 is a variable venturi carburetor with a round slide. The venturi is 37.4mm. It flowed 178 cfm @ 15” H2O. It has no accelerator pump. Installation 3: It was very easy. The only thing that needed alteration was the decompression relay. I had to move it to a frame tube (a simple zip-tie job). Tuning 4: Of the four carburetors, the VM was by far the easiest to dial in. No modifications were necessary to tune the carb, only simple jet changes. It only took a few jet changes to get it just right. All the necessary jets, needles, and slides are provided in Lancer’s kit, and if you need more, they are readily available. Final jetting for this engine setup was: Main Jet #210, Pilot Jet #22.5, Needle Jet #166-Q2, Jet-Needle 6DP1 (clip in middle groove), Main Air Bleed #0.5, Slide cutaway 2.5, Float Level 19mm, Air Screw 1-5/8 turns. Drivability 4: It is an excellent carburetor for a daily driver or a hotrod. Starts easy, almost always on the first crank. Quick warmup. Idles smooth. Great throttle response. No hesitation. Super-smooth cruising. No afterfire on deceleration other than a pleasant (to me) cackcle/crackle, no KABOOM. Acceleration 3: The VM38 pulled a 4K to 7K time of 2.90 seconds. It is tied for the 2nd fastest slot. Fuel Economy 4: The VM38 got 59.2 mpg (best in test). Maintenance 4: Maintenance on the VM38 is about as good as it gets. Accessibilty is good. Complexity is low. Very simple. It’s easy to remove and replace this carburetor, and there’s ample room to remove the float bowl with the carb installed on the engine. There’s a plug in the float bowl for main jet replacement and/or draining water and sediment. Total score for the VM38 is 22. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:18:26 Mikuni VM38 Points of Interest Lancer’s VM38 kit had almost everything I needed to install and fine tune the VM38. I had it running great in about three or four hours. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:18:59 This is the business end of the VM. Note the removable main air bleed (nice tuning feature) and the float bowl drain plug (provides access to the main jet). That big venturi is good for about 178 cfm @ 15” H2O. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:19:30 The VM uses an old school round slide with a tapered needle. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:20:00 It’s a snap to swap out a main jet or dump water and sediment when you have one of these (drain plug). It’s also a good idea to always convert the pan-head screws to socket-head screws, makes life a whole bunch easier. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:20:33 The inner workings of the VM are typical of most any carburetor, except it uses a unique float arrangement where the floats remain in the float bowl (on long slider pins) while the needle & seat are in the carb body. Main jet and pilot jet are standard fare. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:21:03 Here you can see how the floats are arranged in the float bowl. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:21:45 Installation and maintenance are a cinch. There’s lots of room, even with the stock battery box. Fuel line, vent tubes, and air boot all hook right up, almost like the stocker. It’s also easy to remove the float bowl without removing the carburetor (especially if you covert to socket-head screws). |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:22:24 Here’s the solution for the decompression relay. The 90°elbow on the throttle cable hits the relay, so you must move the relay to a new location. I simply zip-tied the relay to the frame tube. Works great. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:25:56 Keihin PWK38 Air Striker The Keihin PWK38 Air Striker is a variable venturi carburetor. It uses a semi-flat slide. The venturi is 37.8mm. It flowed 186 cfm @ 15” H2O. It has no accelerator pump. Installation 2: Although this carburetor doesn’t come in kit form, it is still very easy to install. I only spent about three hours to install the carb and fire up the engine. That included time spent taking photos and tearing down the carb so I could see what makes it tick. My special air filter setup clamped right up, and I used the Barnett cable that came in Lancer’s VM38 kit. I had to enlarge the slot in the fitting that accepts the cable barrel. That was it. The decompression relay was fine right where I had it zip-tied. The stock carburetor manifold was a tad loose, but it worked just fine with a narrow stainless-steel worm clamp. If you prefer a tighter fit, a Mikuni rubber mounting flange (part number HS42/018-42K) works perfect. If I had not already installed the VM38, I would have had to procure a cable that fits. I also had to modify the fitting for the cable and come up with a narrow stainless-steel worm clamp. The PWK was a bit harder to install than the VM. Tuning 3: The PWK38 was easy to dial in but the jets provided with the carb were way too big. The needle that comes with the carb has no markings, so it had to be identified through measurement. It’s an EGN. I had to find and purchase needles, main jets, and pilot jets. The grooves in the new needles are narrow and would not accept the e-clip. This carburetor only costs $75 (from DCMotive), so it’s easier to forgive the narrow selection of jets included with the carb. No modifications were necessary to get the carb to function properly, but the jet-needle had to be changed from an EGN to an EEN. Once the needle was replaced, it was easy to tune. A complete selection of jets, needles, and slides are readily available for the PWK. Final jetting for this engine setup was: Main Jet #140, Pilot Jet #40, Needle Jet as delivered (fixed .114”), Jet-Needle EEN (clip in 2nd groove), Main Air Bleed as delivered size unknown, Slide Cutaway 7.0, Float Level: level with carb inverted, Idle Mix Screw 1-3/4 turns. Drivability 4: It is an excellent carburetor. It drives almost identical to the VM, hard to tell them apart when you’re in the saddle. Acceleration 4: The PWK38 pulled a 4K to 7K time of 2.82 seconds. It was the fastest. Fuel Economy 3: The PWK38 got 57.2 mpg (2nd best). Maintenance 4: All aspects of maintenance on the PWK38 are essentially identical to the Mikuni VM. Access, adjustment, etc. are almost identical. Very simple. Total score for the PWK38 is 20. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:27:17 Keihin PWK38 Air Striker Points of Interest I got the Keihin PWK38 from DCMotive. It’s not a kit, just the carburetor and a small package of extra jets. At $75 bucks the price was right, and it was at my door just two days after I placed the order. The jets were too large, and the needle was too lean, so I had to come up with a variety of jets and needles. My air filter clamped right up to the PWK and Lancer’s throttle cable had just enough adjustment to work with the Keihin carb. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:27:52 This is the business end of the PWK. That big venturi is good for about 186 cfm @ 15” H2O. The fin things are air vanes (the “Air Striker” feature that supposedly amps up the venturi vacuum signal). |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:28:23 Just like the Mikuni VM, it’s easy to swap out a main jet or dump water and sediment because the PWK has a drain plug. Here you can see the pan-head screw vs socket head screw, the socket heads are much better, always do the conversion. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:28:58 The inner workings of the PWK are typical of most any carburetor, float, needle & seat, main jet, pilot jet, etc. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:29:30 The PWK uses a formed rubber seal on the float bowl in lieu of a fiber gasket. That’s a nice feature until you need a new seal. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:30:04 This cobby drain plug O-ring had to go. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:30:34 I replaced it with a viton o-ring. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:31:08 This is the unusual semi-flat slide. Sort of half round, half flat. It works well. That little doohickey on the right is the piece that I needed to enlarge the socket in (to accept the cable). |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:31:43 Replacement needles were needed to dial in the carb. It came with a EGN, too lean. ECN & EEN replacement needles were both an improvement. I settled on the EEN. Note that I had to sand down the e-clip to thin it out enough to fit in the needle grooves. I used a strong magnet to hold the clip for sanding. You can see that the grooves in the as-delivered EGN needle are wider than the replacement EEN needle. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:32:18 The stock rubber manifold works OK with the PWK but the fit is a bit loose. The stock clamp won’t fully tighten the connection. A narrow stainless-steel worm clamp tightens it right up. An Ideal 5/16” wide #36 clamp works good. If you prefer a real tight fit, pick up a Mikuni manifold (part number HS42/018-42K). It’s a perfect fit. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:32:54 With the PWK, installation and maintenance are easy. There’s lots of room, probably even with the stock battery box. Fuel line, vent tubes, and air boot all hook right up, almost like the stocker. It’s also easy to work on the carb without removing it. Idle speed & mixture adjustments are easy to access. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:36:11 The Old School S&S Super-E. The S&S Super E is a fixed venturi carburetor. It’s 19th century technology at its finest. The venturi is 40mm. It has an adjustable accelerator pump. It flowed 191 cfm @ 15” H2O. Installation 1: This carburetor was not intended for installation on the Savage, it was designed for a Harley Davidson V-Twin. The Super-E was VERY difficult to install on the Savage. Tuning 1: The Super-E was equally difficult to dial in. It required modifications to the intermediate and main air bleeds, and countless hours of fiddling around with emulsion tubes, transition ports, float level, mixture settings, insulator blocks, etc. It was a challenge. Final jetting for this engine setup was: Main Jet #68, Main Air Bleed #140 (Mikuni), Intermediate Jet #26.5, Intermediate Air Bleed #80 (Mikuni), Float Level 1/16”, Idle Mix Screw 1-3/4 turns, accelerator pump 1 turn. Drivability 2: It is an OK carburetor for a daily driver and a fun carburetor for a hotrod. Drivability is sketchy. It starts easy, almost always on the first crank. Quick warmup. Idles OK. Great throttle response (really raps when you whack it). Sometimes runs rough & hicups. Cruises a bit choppy. No afterfire, no KABOOM. Acceleration 3: The Super-E pulled a 4K to 7K time of 2.90 seconds. It is tied with the VM38. Fuel Economy 1: The Super-E got 49.2 mpg. Dead last. Maintenance 4. Maintenance on the Super-E is super. You don’t have to remove the carb for much of anything. Minor adjustments to the mixture can be accomplished by swapping air bleeds (which are external). Removal and replacement of the entire carb is also very easy. The float bowl has a plug so draining the bowl and changing the main jet is easy. Total score for the Super-E is 12. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:37:12 S&S Super E Points of Interest This is the business end of the Super-E. That huge fixed-venturi is good for about 191 cfm @ 15” H2O. Since the venturi is fixed, it pulls the least venturi vacuum at part throttle, so fuel atomization and distribution are much less efficient. That’s really apparent in the drivability and economy categories. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:37:52 To install the Super-E on the Savage, I needed a custom intake manifold. That turned out to be a lot more difficult than I anticipated. I spent a lot of time just machining the manifold. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:38:22 To connect an air filter, it needed an air horn too. More raw material, more machining. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:38:53 For the stock throttle cable to fit the S&S cable bracket, the 90°elbow must be modified, and the barrel end too. That was one of the easy parts of the install. The modified cable is on the left, stock cable on the right. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:39:29 The float assembly and needle valve are part of the float bowl, so checking and adjusting float lever are as simple as removing the bowl, you don’t have to pull the carb. However, it is very easy to remove the entire carburetor too. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:40:05 Changing a main jet or draining slop out of the bowl are as simple as removing this plug. Of course, socket head screws are a must for securing the float bowl to the carb body. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:40:35 Adjustable air bleeds had to be set up for both the intermediate jet and the main jet. Regular Mikuni large round jets are used. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:41:07 A lot of time was spent experimenting with transition ports. I tried adding a fourth port, and then had to fill it back in. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:41:41 Once installed, the Super-E almost looked like it belonged on the Savage. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/28/20 at 23:44:18 So, there you have it. Four carbs, one winner. Based on the scores, the Mikuni VM38 is the champ. It excels in all categories, and in my informed opinion, really is the sweetest mixer in the bunch. It is also the most flexible. The replaceable main air bleed and needle jet provide additional tuning options. It provides great drivability and performance with a healthy dose of fuel economy. While the VM is clearly the winner, I think the Keihin PWK38 is a mighty close second. Both carbs are almost flawless. Don’t overlook the stock carburetor. This test shows that it will perform well on a highly modified engine. It requires a bit of tweaking, but it will reward you with good results if you are willing to spend the time and effort. Obviously, it will never keep up with the other mixers in a drag race, but it will support a lot more performance than the bone stock engine produces. I must admit, I really wanted the Super-E to pull a rabbit out of the hat. It’s tough to make the case when the other mixers are so darned good. She has served me well for over 30 years, but I think it’s time for her retirement. There will always be a place in my heart for the Super-E. I hope this report will provide you with some good information. The installation notes and photos should help you plan for a carb swap, and the jetting data I listed will get you pretty close on an engine with similar modifications. Knowledge is power. Stay well. Mike |
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Title: Re: Carburetor Shootout Post by Gary_in_NJ on 03/29/20 at 05:31:37 Excellent post. Informative, to the point and even entertaining. Great science Mike. I’ve used 3 of these carbs (never had a Super E) as well as others (my DRZ has an MX39 pumper...a real pia to diagnose). I think the most important aspect of any carb is to understand how it works and what each jet and passage does. With that understanding tuning, maintenance and troubleshooting become very easy. As you proved/showed in your last carb comparison, at WOT there isn’t a big difference between carbs with similar Venturi openings. However throttle response can be very different. I find that the stock carb works very well on my mostly stock engine. However, if I ever install performance cams and a HC piston, I’ll be looking for a VM kit for sure. |
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Title: Re: Carburetor Shootout Post by Armen on 03/29/20 at 06:51:51 Excellent post, Mike! As with all your posts, well written and photographed. Which wide band O2 do you use? I have a Mikuni RS40 on mine. Only ran it for a minute or two, seems fine, but I'm sure I'll be twiddling and fiddling. Have to say, the Lancer kit seems pretty sexy! Someone once described an S&S as a trash can with a trap door. Good for farm equipment and old HDs, but not much to talk about compared to modern carbs. thanks so much! -Armen |
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Title: Re: Carburetor Shootout Post by Dave on 03/29/20 at 08:50:44 1F19166A686F6B5B0 wrote:
Mike: Great review, and it supports my experience with this bike. I am not a drag racer - my engine modifications were intended to make a better running engine. Not necessary the best - but better. My rides are generally on 40-60 mph twisty back roads, and my rides are spirited -but generally don't require more than 1/2 throttle at any point during the rides. I stay at the speed limits on the straight sections, and I try not to slow down much for corners......my fun is on the curves! I ran the stock carb and air box and paper filter for a year after adding the Wiseco 95mm, performance cam, head porting and less restrictive exhaust. The engine ran great and was a lot more fun than the stock engine. When I switched to the Mikuni VM38, the only real change I noticed was a bit faster throttle response - but we are talking tenths of a second of change.....it just felt like the throttle was more directly connected to the engine. On a normal ride either carb proved to work very well as I tend to roll on the throttle - I seldom "wack" open the throttle instantly. The only negative I have about the VM38 - is that if you set the carb up for a 1,100 RPM idle, and you have to do a panic stop and pull in the clutch and chop the throttle instantly while you brake hard - the engine can stall as a result of the instantly closed throttle. The higher compression piston and light flywheel may also contribute to the problem. I believe the stock CV carb and TEV valve are a bit more reliable in the chopped throttle scenario. Rejetting the carb richer at idle or increasing the idle speed would help with the chopped throttle stalling scenario - but the current jetting is set up so the bike runs well during normal operation, and I am not willing to rejet to resolve an issue that only occurs a couple times a summer. So......I am supporting the use of the stock carb - it really is a decent carb. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/30/20 at 15:28:37 Gary, if you get around to installing a bigger bump-stick and HC piston, don’t hesitate to massage those ports. The stock intake port flows very close to the stock carburetor, so you really won’t get much out of a bigger carb unless you work the ports. The stock carb flows 159 cfm vs the stock intake port’s 167 cfm, fairly close. If you work the intake port similar to what I have posted here (epoxy and re-shape), you can get that intake port flow up to 195 cfm. A much better match for a 38 or 40mm carb. Armen, “Trash can with a trap door”, harsh Dude [ch128522]. That old Super E was sweet on my Harley. Every bit as good as the stock Harley Keihin CV and the Mikuni HS40 I tried. But hey, the S&S was specifically designed for the Harley. The Savage? Not so much. My A/F meter is a AEM model 30-4110 UEGO. It’s not a Cadillac but it gets the job done. I was able to install the O2 sensor without welding. Fabricated a bolt-in bung from a 1”-14 bolt and nut. Have to fish the nut in through the muffler inlet. A bit tricky but doable. The meter is one of those temporary installations that never seem to get removed. I really should clean up the gage mount. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/30/20 at 15:31:06 This shows the O2 sensor in the muffler. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/30/20 at 15:32:00 I dial in the WOT A/F ratio as close as I can get it (safely) and then finish up by recording vids of the meter as I accelerate onto the freeway in 3rd gear. I take it all the way to 7500 rpm. Then I review the vids in the safety of my home office. Make the final jet changes based on the vids. Then re-check. It’s way safer than trying to stare at the A/F meter while you’re running up to 7.5K (Hey! Keep your eyes on the road). I have a hood that eliminates all the glare, so the vids are crystal clear. I love the Go-Pro setup. It takes a lot of guesswork out of test & tune. I got the idea from Verslagen. He was using a camera to monitor his float level. How cool is that? |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 03/30/20 at 15:33:11 Dave, I agree the stock carb suits your riding style. It’s in the sweet spot right where you do most of your work. Power delivery is linear. Very good match. BTW, I also experienced that panic stop stall with the VM. It only happened once. Mikuni used a baffle on some of the older off-road applications. It supposedly prevented the fuel from sloshing around in the float bowl. That part might still be available. It was held in place by the main jet (as I recall). If you look at the picture of the PWK internals, Keihin appears to have incorporated a similar built-in baffle that should mitigate fuel slosh. |
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Title: Re: Carburetor Shootout Post by ZSteele on 04/02/20 at 07:55:31 So when are you getting a lectron carb? |
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Title: Re: Carburetor Shootout Post by verslagen1 on 04/02/20 at 10:35:39 72747B07050206360 wrote:
The edelbrock quicksilver has a baffle and foam in the lower half of the bowl. |
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Title: Re: Carburetor Shootout Post by verslagen1 on 04/02/20 at 10:36:29 777E59484841482D0 wrote:
I'm sure mike will gladly accept any donations. |
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Title: Re: Carburetor Shootout Post by ZSteele on 04/02/20 at 11:01:46 Lectron seems to give out a few of their carbs for review, given DBM's testing methods and experience with many carbs it might be worth and email to get one for testing and sharing info with the forum community. If they're as good as they say/seem then I would think they'd love the testing and possible new market. Also thunderproducts has a baffle for the VM's. |
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Title: Re: Carburetor Shootout Post by LANCER on 04/03/20 at 13:07:00 Baffle ? |
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Title: Re: Carburetor Shootout Post by ZSteele on 04/03/20 at 13:37:09 I can't remember if its metal or a plastic material but basically it just sits in the float bowl at what I can only guess is at or above float level and prevents splash up. |
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Title: Re: Carburetor Shootout Post by ZSteele on 04/03/20 at 13:38:37 This: http://thunderproducts.com/product/fuel-baffle/ |
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Title: Re: Carburetor Shootout Post by Gary_in_NJ on 04/04/20 at 06:20:53 Usually the baffle clips to a boss mount at the main jet. Everyone I’ve seen is plastic. |
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Title: Re: Carburetor Shootout Post by SpamyToo on 04/05/20 at 00:48:25 Great write up Mike. Your always so thorough and your pictures are always great. Im curious where you found the EEN jet. This seems to be the white whale of jet needles. I have yet to find one place that carries them. It appears to be stock on a 1988 - 1989 Kawasaki KX125 but doesnt appear to be used anywhere else that I can find. It goes by these names... N427-48 EEN 48-EEN EEN/017-455 R2072J 16009-1414 (for kawi) It shows up in the charts, but actually attaining one is another matter. https://jetsrus.com/a_jets_by_carburetor_type/needle_keihin_N427-48.html I dont doubt your measurements and findings, but the needle that comes with the carb is supposed to be a DDJ (48-ddj / DDJ/017-500 / N427-48 DDJ). Which has the measurements of 36.80mm in length, 2.685 diameter with a 1.45 degree taper. Ill have to check the other ones and see what they actually come with. I ask, because I was trying to offer a kit version as well. Perhaps with a few optional needles. But that one you list is apparently like the most rare jet needle there is. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 04/05/20 at 01:44:32 Spammy, I got the EEN from Jets-R-Us. I just checked their website and I see that there is a place marker between the EGN and the ECN. I believe that place marker is for the EEN. As I recall, the EEN was listed when I purchased. It had to have been listed, otherwise I wouldn't have been able to order it. My invoice is dated 1/28/20, part number N427-48-EEN/017-455. Did you try calling Jets-R-Us? To me, the needle delivered with the carburetor was suspect. Keihin and Mikuni genuine parts usually have their part number and logo. The needle that came in my PWK had no markings whatsoever. Plus the grooves were wider and the e-clip was too wide for the replacements. You might also try Sudco. They sell the PWK too. It would be a shame if you can't get the needle because the carb runs sweet with that EEN. I believe it will probably run OK with the ECN too, but the needle might end up in the max lean position. I was very careful when I measured the needle delivered with the carburetor. It required some simple trigonometry to calculate the angle. It works out to exactly 2 degrees. I'm very confident that the needle that came with the carb is a EGN or equivalent. It was also too lean. My notes show I was able to get it rideable with the EGN by placing the clip in the lowest groove. Might be able to dial it in with a washer or two under the e-clip. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 04/06/20 at 02:58:55 Well lookie here. http://www.sudco.com/genuine_vs_fake_carburetors.html I went on the Sudco website and found this info on fake Chinese knockoff carbs. The unmarked needle is consistent with what Sudco is providing for identification of a knockoff. The hoses are a mystery, I don't know what "PLAS TECH" means. Is that some sort of trademark? Should I expect to see PLAS TECH marked on the hose? The box looks legit, and "made in Japan" is on the box and some included paperwork. The jets have the Keihin logo along with their size designator. There isn't a serial number anywhere on the carb. If the PWK I have is a knockoff, the Chinese are getting awfully good at it. The fit & finish quality of the PWK actually seems a bit better than the VM (with the exception of the drain plug o-ring). All's I can say is it runs and looks good. :o |
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Title: Re: Carburetor Shootout Post by ohiomoto on 04/10/20 at 14:08:02 00060975777074440 wrote:
Jets-r-us... LOL RANT coming! They say "All sales are final" for good reasons. They are saying don't oder if you don't know what you want. Make sense. What doesn't make sense is that when they send me the wrong jets as in not the ones I ordered and not the ones listed on packing slip. They expect me to pay to send them back. But they clearly state they don't take jets back because they can't sell them allegedly. They could have been drilled out. So why do they want it back now??? They expect me to pay for their mistakes. How about you send me the jets I ordered and I'll throw our mistake out. Or you pay shipping if you must have them back (even though you state you'll never take jets back). And yes, we are talking about $5 but it's the principle of how they decide to do business. End rant. :) |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 04/11/20 at 02:25:27 I can't complain about Jets-R-Us. I have ordered a ton of jets and parts from them. They sent me the wrong item only once. I didn't bother to complain. I guess if it had been something I absolutely had to have right away I would have been ticked off. I get the parts within four or five days, and they charge a flat rate of $7 bucks for shipping. In contrast, I ordered a couple of pilot jets from Dennis Kirk. They sent the two teeny-weeny jets in a medium flat rate box. Shipping was over $10 bucks as I recall. Now that's hosed up. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 04/29/20 at 13:52:45 Regarding the questions pertaining to the baffle for the Mikuni VM38, this is a picture of a Honda dirt-bike carburetor that Dave has been working on. The white plastic piece is the baffle in question. The baffle helps to keep the fuel from sloshing away from the main jet. I've also seen baffles made from brass, and in the case of the PWK the baffle is integral to the casting. The baffle is typically used on off-road vehicles because they shake the carbs up pretty good. Don't usually see the baffles on street applications. Thanks for the pic Dave. |
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Title: Re: Carburetor Shootout Post by SpamyToo on 08/31/20 at 04:47:31 For the Keihin and Keihin type carbs that Mike tested here I have revamped the selection and stocked up again. There were some waiting and I thought this excellent write up should be bumped anyways. https://dcmotive.com/products/keihin-38mm-pwk38-carburetor (Sorry no cables with the kits, thats Lancers forte. Order from him or adapt your own) |
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Title: Re: Carburetor Shootout Post by zipidachimp on 09/01/20 at 02:52:42 If the VM38 works so well, can we assume the VM36 is no longer an option? Cheers! 8-) |
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Title: Re: Carburetor Shootout Post by LANCER on 09/01/20 at 04:37:23 They both work quite well. I do think the 36 has an advantage in the low-mid range due to the fact that a smaller tube will pass a given amount of air through it at a higher velocity than a larger tube, which will pull the fuel up more efficiently and make power more efficiently. The 36 is not deficient. I have a part for a ‘91-later Sportster Carb Kit using a 36mm Carb. If it will feed a Sporty it will feed a Savage. It can move all the air you will ever need in it. I sell both and like both, I also like to focus on the best characteristics of the LS engine which is low-mid grunt & pull. That’s a big single. To me the 36 works slightly better for the job in my engine. I have a Stage 3 cam which has a lower max lift than some the DR’s and so don’t need to try for more air than is provided abundantly already. My first big single ran a 38 Amal Grand Prix carb on the mile ovals in the 50’s-60’s. I got it in ‘69. That was a nice one. [ch128526] High range performance is excellent, identical to the 38 on my bike. |
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Title: Re: Carburetor Shootout Post by elysianforest on 10/02/20 at 12:25:27 So I just wanted to share a trick I figured out this week for anyone considering the 38mm PWK... You can reuse the stock intake hose by reversing it and adding a little extension tube to the airbox. About 40mm chopped off the tapered end of a shop-vac extension tube is an absolute perfect fit. I went ahead and used a tiny bit of pvc glue, more for sealing purposes than retention, but that's probably not necessary as the fit is so good. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 10/02/20 at 13:51:04 Elysianforest, how do you like the PWK? Fill us in on your setup. Did you find the installation easy or difficult? Have any problems dialing the carb in? Can you post a few pics to elaborate on your air-boot mod. Regards, Mike |
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Title: Re: Carburetor Shootout Post by elysianforest on 10/02/20 at 16:21:31 Hey DBM, So, I actually just installed it yesterday. I'll let you know once I've got her buttoned up. I'm still waiting on Verslavy's tensioner and head plug mods, but have also just put in Lancer's stage 3 cam, and am currently devising how I'm going to rig up a glass pack muffler I got that is meant for a Royal Enfield. I found install to be pretty easy overall. I chopped off the end of the stock throttle housing to the little part which fits right into the PWK. I used a cable repair kit (which works fine when soldered) to get the correct ends and length on the cable itself. |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 10/03/20 at 15:42:02 Cool the way you repurposed the intake boot and used the section of shopvac tubing to extend the airbox nipple. I like it. By any chance, did you take any photos of your cable mods? Can you provide more detail on the cable mods. I know someone who might appreciate that info. Keep us posted on the tuning. It will be very helpful to know how that goes. |
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Title: Re: Carburetor Shootout Post by Kwarran on 02/02/23 at 00:47:29 DragBikeMike, I went with the Mikuni VM38 carb, but I don't get something. I thought it's better to ask here than to make a new thread. What do you do with the vacuum line from the petcock? And when running the motorcycle you have to put the petcock on PRI? Because I noticed there is no vacuum line on the VM38 carb |
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Title: Re: Carburetor Shootout Post by TheSneeze on 02/02/23 at 07:32:36 Switch your petcock to a genuine Yamaha Raptor 660 petcock (no vacuum feed), and plug off the vacuum nipple on the carb. |
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Title: Re: Carburetor Shootout Post by ThumperPaul on 06/10/23 at 12:47:00 Hey Mike. Incredible study here!! I have a question that is in no way urgent or terribly important and I know it's the weekend, but I do want to pick your your big brain and put it out here to share! If you could kindly respond when you get a moment I would greatly appreciate it. I think you know I installed a PWK40 carb (knock off) on my bike (stock bike except for Jardine exhaust and air box cover removed). The bike is running quite well, but I'm getting poor gas mileage (like 40mpg) virtually regardless of how aggressive I ride be it in suburbs or highway. You may recall that I've rejetted several time and I'm running a #48 primary and #162 Main. I think you commented those seemed really big and I agree, but I'm really not running too rich (performance-wise is good throughout, spark plug check, exhaust pipe check). After seeing your test results and especially CFM stats, and learning about the venturi effect, fuel atomization, and more than my novice carb-tuning brain can handle.... My theory/question: The PWK40 carb is just simply too big without any other engine mods (intake porting, cam, piston, valves, etc). I think I'm having to "jet up" really big to mix up enough gas with all that air to get the correct air/fuel ratio. I think I've basically force tuned a fat carb on the bike and gas mileage is showing the gluttonous appetite. Your results for the Harley SS carb really got me thinking down this path. Thanks in advance for your thoughts and expertise!! |
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Title: Re: Carburetor Shootout Post by DragBikeMike on 06/10/23 at 18:53:14 "My theory/question: The PWK40 carb is just simply too big without any other engine mods (intake porting, cam, piston, valves, etc). I think I'm having to "jet up" really big to mix up enough gas with all that air to get the correct air/fuel ratio. I think I've basically force tuned a fat carb on the bike and gas mileage is showing the gluttonous appetite." I managed better than 50 mpg with the PWK38 on this carb shootout. If you go back to the section that tested the PWK it should give the exact data. That was with a hopped up engine. On a completely stock engine, the PWK 40 averaged 55 mpg. This post provides the details on that test. Jetting was similar. http://suzukisavage.com/cgi-bin/YaBB.pl?num=1625732492 For some reason, you are running much larger jets. I looked to see if I have any photos of your carb. I don't seem to have any. Possibly if you post a set of photos, we can figure out why you need those large jets. |
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