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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> PWK40 Knockoff with E-Tube /cgi-bin/YaBB.pl?num=1690104776 Message started by DragBikeMike on 07/23/23 at 02:32:56 |
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Title: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:32:56 I have been dyin to get my hands on one of these for a long time. It may look like a regular Keihin PWK carb, but it’s a knockoff with an unusual brass contraption between the metering block and the main jet. The Duderino has one, ThumperPaul has one, and The Sneeze has one. I was anxious to learn more about it. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:34:37 Both the Dude and Sneezy got their carbs from JFG Racing. I’m not sure where ThumperPaul got his. When I searched the web, I always came up dry. Then I found this. The Amazon add said the brand is “JFG Racing” and the seller is “Jin Yao”. I decided to take a chance. This is the link. https://www.amazon.com/Carburetor-Universal-Compatible-Scooter-Motorcycle/dp/B094NJ466C |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:35:38 It’s a knockoff, and like all knockoffs there’s risk. I might end up with a standard PWK like the ones I already have. Curiosity overwhelmed me. I really wanted to know exactly what’s inside one of these newer knockoffs with the unusual brass jet holder. The minimal entry fee was worth the risk. I ordered it, and in about four days the box was in front of my door. That was a big improvement over the one-month wait time for the last knockoff. There isn’t much difference when looking at the outside of the carb. On the left side, you can see that the plastic idle stop screw has been replaced with a brass screw (nice upgrade), and you can see that the idle air screw looks different (it sticks out a bit and the head is larger). Other than those two items, it looked the same as the other knockoffs I had purchased. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:36:31 I screwed the top off and was pleasantly surprised. The slide looked good. The chrome plating was a lot better. This is the load bearing side. The chrome looks smooth, no pits or bubbles. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:37:03 The upstream side had a few funky spots, but overall, it was much better than the previous knockoffs. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:37:39 It’s a #7 slide. A letter “W” drill bit fits under the edge of the cutaway. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:38:21 The slide needle is different. The basic diameter is a lot smaller. None of the available Keihin needles are close to this small. If it needs a new needle, I am out of luck. Here it is next to a genuine Keihin DGK (DGK on top, new needle on bottom). |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:39:11 Remove the float bowl and you will immediately see that the main jet configuration is different. There is an extra brass piece. Unlike the older knockoffs where the main jet was threaded directly into the aluminum metering block, these newer versions have some sort of brass piece between the metering block and the main jet. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:39:51 Turns out the brass piece is an emulsion tube. I’ll refer to it as the “E-Tube”. Those little holes in the side of the tube alter the fuel delivery curve and admit air bubbles into the liquid gasoline. The bubbles mix with the liquid and form an emulsion (i.e. foam). The foam is lighter, so it responds faster to changes in vacuum, and promotes atomization. That’s my limited understanding of the concept. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:40:46 For wide open throttle (WOT) operation, the holes at the top of the emulsion tube affect lower rpm, and the holes at the bottom affect higher rpm. Whack the throttle wide open at 2500 rpm, and the holes at the top of the tube come into play. As the fuel level in the emulsion cavity goes down, it begins to uncover more holes, so at maybe 4000 rpm the holes in the middle of the tube come into play. By the time the engine reaches 6000 rpm, the fuel level in the emulsion cavity has uncovered the holes at the bottom of the tube, so now all the holes are in play. It works like a soda straw that has holes in the side of the straw. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:41:23 Put the straw in a glass of KoolAide (I like lime). When you first start drinking, it doesn’t take much suction to get the KoolAide up the straw. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:42:01 But as the level of KoolAide goes down, it starts to uncover holes in the side of the straw, and those holes permit air into the straw. The air breaks the vacuum. So, you must compensate by sucking a little harder. As the level of KoolAide continues to drop, you must suck harder and harder to get a mouthful. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:44:51 Venturi vacuum vs air flow is a quadratic function. It is not linear. As air flows through the venturi, the vacuum at the top of the needle jet increases exponentially. So, when the air flow doubles the vacuum increases like four times. That makes the fuel mixture go richer and richer as the rpm increases, but you want the air/fuel ratio to remain relatively constant (about 12.5:1). To compensate, carburetors use air correction to try and maintain a reasonable mixture over a wide range of rpm. The standard PWK and the Mikuni VM use a simple air correction system that does OK, but it fails to achieve a perfect air/fuel ratio over the entire range. Both these carbs go rich at high rpm (when the throttle is wide open). That’s why the aftermarket has come up with third fuel circuits like the “Thunderjet”, or the “Dial-A-Jet”, or the “InteliJet”, or the “Power Jet”. You can put in a larger main airbleed to try and correct the rich condition at high rpm, but then you end up with a lean condition at lower rpm. You can put in a smaller main jet to try and correct the rich condition at high rpm, but that will also result in going lean at lower rpm. You can fiddle around with the airbleed and main jet until you go nuts, but you will probably never be completely satisfied. This problem only pertains to WOT conditions. At part throttle, the needle jet and slide needle are takin care of business. But snap the throttle all the way open and those two components are out of the picture. At WOT, you are relying on the main jet and air correction system to deliver fuel at the proper ratio. That’s a tall order for a fixed jet with a fixed airbleed. The emulsion tube offers a little bit of relief. As the venturi vacuum increases exponentially, the fuel level in the emulsion well is dropping, and more emulsion holes are being uncovered. The additional air correction helps to compensate for the exponentially higher vacuum. It’s not perfect, but it should be an improvement over a simple airbleed system that only admits air at the very top of the needle jet. With an emulsion tube, the naturally occurring drop in fuel level adds more air correction as the rpm rises. It adds another dynamic component to the air correction system. This YouTube vid does a nice job of explaining the quadratic behavior of a venturi. https://www.youtube.com/watch?v=BvOqNwNuuAA |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:46:11 Just above the emulsion tube is the needle jet. It comes right out when you remove the emulsion tube. Here’s a look at how things stack up in the metering block. Fuel enters through the main jet and fills the emulsion tube and surrounding cavity. At idle, the fuel level in the cavity is the same as the fuel level in the float bowl. As engine speed increases, the fuel level in the cavity begins to drop because the main jet restricts the flow of fuel into the emulsion tube. Pretty clever. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:47:30 With the E-Tube and needle jet removed, you can see how the main airbleed passage ties into the emulsion cavity. Just shine a flashlight up the hole in the metering block and look through the main airbleed. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:48:52 The hole through the center of the emulsion tube is .111”. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:49:40 But the hole in the needle jet is .101”. The needle jet is the controlling orifice, and it works in conjunction with the tapered needle to form the aperture that controls fuel flow during part throttle operation. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:50:34 Here you can see the needle jet nested just behind the hood in the venturi. On the earlier knockoffs, you won’t see this brass piece sticking up. Looks like we have a quick & dirty way to see if we have the latest version. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:52:10 Since the needle jet is only .101”, a standard PWK slide needle won’t fit. The smallest basic diameter OEM needle is 2.605mm, that’s .1026”. Not gonna fit. Gotta trust that this thing runs good with the as-delivered needle. If it doesn’t, I will have to get creative. Here is a DGK needle stuck in the .101” needle jet. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:53:11 I could see that the main airbleed on this new carburetor is significantly smaller than the original PWK knockoffs. My PWK36, PWK38 and PWK40 all had .075” main airbleeds. The new E-Tube carb has a .039” main airbleed. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:53:47 A .039” pin gage just fits. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:54:53 I find the smaller main airbleed an interesting tidbit. Some of you may recall that a few months back I did a post on modifying the older PWK knockoff by installing a replaceable main airbleed. In that post, I achieved a better fuel curve with a .032” main airbleed and a much smaller main jet (#135). What a coincidence. http://suzukisavage.com/cgi-bin/YaBB.pl?num=1676333024 |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:55:35 I suspect that I could get at the needle jet in my older knockoff carb if I was willing to remove the metering block, but those tamper-proof screws are an indication that someone smarter than me doesn’t think I should be messin with that. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:56:28 I recall seein on some other sites that the metering block can be difficult to seal up. It has several air and fuel passages that interconnect, and it also has a joint between the float bowl and the venturi. Looks like a can of worms to me. Glad someone else figured out a way to get at the needle jet without disturbing the complicated joint. This is the seal used between the metering block and carb body. No thanks. Emergency use only. Why struggle. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:57:12 This is the new idle stop screw. All brass, sweeeeeet! Nice rounded nose. Looks much better. I like the way the PWK carb has this screw captured. I snapped one of these off on a Mikuni VM years ago. It went straight into the engine and finished the motor off. RIP. This one can’t get out of the cavity. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:57:55 The idle air screw is a bit different. Might be easier to adjust. The screw head is a little larger. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:58:35 The float has a nice feature. They have added a brass bushing for the float pin. There’s a lot less slop in the mechanism. It swings free but doesn’t wiggle around as much. This should be an improvement, but I have never had any issues with the original float. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 02:59:19 I measured the bore of the carb. It’s billed as a 40mm. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 03:00:16 Even says so on the side of the carb (tee hee hee). |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 03:01:00 But just like my current knockoff 40, it’s only 38mm. That’s OK, I’m already havin trouble keepin things glued together with a 38mm carb, I don’t need a 40. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/23/23 at 03:03:03 The carb came with a #170 main jet and a #50 pilot jet. Don’t know what these jets would be used on. I suspect a very large two-stroke engine. In Savage Land, those jets are like a flash-flood. I will probably start with a #140 main and a #35 pilot, needle clip in the center groove. I am cautiously optimistic about this new knockoff. I like the idea of having the emulsion tube to flatten out fuel delivery, and the other new features look like they will improve the carburetor as well. Overall quality looks good. I can’t wait to try this carb. My old school PWK is running well. It purrs like a kitten and roars like a lion. It will be a hard act to follow, but there is always room for improvement. Maybe I can squeeze out a few more miles per gallon, or get crisper response. As a minimum, I will learn a few things. If any of you have a PWK knockoff with the E-Tube, please share your experience. How does it run? Was it hard to tune? How’s your fuel mileage? Starting, idle, throttle response, power??? I am currently doing a long-term test on my lubrication system. I don’t want to change anything while I’m in the middle of that test. I want to go 10,000 miles and then do a thorough inspection to verify that the gears and bearings are holding up. If all goes well, I should be installing this new E-Tube carb in a couple of months. Stay tuned. |
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Title: Re: PWK40 Knockoff with E-Tube Post by ThumperPaul on 07/23/23 at 16:49:30 Hey Mike! Amazing analysis!! I really liked the Kool Aid illustration. LOL. I bought mine from USAMOTOKING. https://www.ebay.com/itm/155136268286 I actually sold my S40 project, but still checking-in here for good stuff like this. As you recall, I kinda called it good enough at a #40 pilot and #145 main with the Jardine exhaust. If I would have kept the bike, I could have dropped down to a #38 primary. I ended up landing at about 50mpg which was my goal after correcting those big jets and loose manifold connection (again, thanks for all your guidance on that!!). I honestly don't fully comprehend a lot of your analysis, but it doesn't sound like you found anything significant enough to alter your mind about starting with a #35 and #140, huh? Let us know how it goes! I'm interested! FYI - I bought a 2006 Honda Shadow Spirit VT750DC in mint condition and only 2600 miles. It was owned by a guy that treated it like a trophy bike in his garage and I got a great deal. I couldn't pass it up. I'm really enjoying it! |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/29/23 at 10:48:09 Paul, sorry to hear you switched rides. :'( What can you tell us about the Honda in comparison to the Savage? Maybe you could do a comparison and post it. Power, comfort, handling, brakes, suspension, etc. How my Savage 650 stacked up against my Honda 750. Thanks for the info on your source for the carb. Looks like they're right around the corner from Dave and they suggest it for a honkin BIG 2-stroke. |
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Title: Re: PWK40 Knockoff with E-Tube Post by ThumperPaul on 07/29/23 at 14:37:20 I am looking for my next Savage project. I love the smoothness of the Honda and its stability over 65+mph (night and day comparison). I wanted something that I would feel a little more comfortable, stable, and confident on the highway for the occasional times I highway ride. I do miss being able to flick around the Savage. The Honda is about 520lbs compared to 380 for the Savage (wet weight comparison). Tinkering with the Savage is way easier! The VT750 has dual carbs and I just pray they stay in sync. I don't have the equipment or know-how to sync carbs. Dialed in the air/fuel mix hoping I'm properly synced. I think it is. The prior owner had the carbs cleaned/rebuilt by a buddy. The air box duct work wasn't put back together well and I had to get all that straightened out and dial-in the air/fuel mix. Runs great! Looks awesome! I think you're right about it somewhat intended for a big 2-stroke. I think some ads referenced a big Honda 500 2-stroke. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 07/30/23 at 16:09:54 Paul, you weren't kiddin when you said that Honda is in mint condition. That's a beauty. Thanks for sharing the pic. |
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Title: Re: PWK40 Knockoff with E-Tube Post by ThumperPaul on 07/30/23 at 16:16:52 Thanks Mike! I couldn't pass it up! It's like new. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/12/26 at 22:12:41 Wow! Time flies when you’re havin fun. Hard to believe it’s been 2-1/2 years since I did the original post. I was closin in on 100,000 miles and decided to test this E-Tube carb before I did the 100K teardown. It required that I resume beating the hell out of my hotrod, so I hope I didn’t screw up the long-term test of the gearbox and oil system. The engine had been running superbly. Loads of power and torque, easy starting, smooth idle, no leaks, minimal oil consumption, great fuel economy. It’s noisy, but I have way too much piston-to-cylinder clearance, so the cacophony is not surprising. To get started, I set up the GoPro on my tach and did a whole bunch of timed tests to make sure I had the standard PWK jetting as good as possible. The current engine combination utilizes a 4-speed transmission so I can’t compare the performance to the testing I did several years ago with a 5-speed setup. The gear ratios on the 4-speed are a lot taller than the 5-speed. I am also running a larger circumference rear tire which makes the final drive ratio taller as well. It doesn’t accelerate nearly as fast as the 5-speed setup, but at least I have a solid set of data to compare the E-Tube carb to the standard PWK. I’m hopin the E-Tube carb will improve the WOT performance. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/12/26 at 22:14:28 First order of business was to make an adapter sleeve so I could use the stock intake manifold. It would be much easier to use an aftermarket manifold, but I prefer the stock manifold. It’s a top-quality piece. The PWK will fit in the stock manifold, but it’s a bit loose and requires the use of a special hose clamp. I’ve done that and it works OK, but a good tight fit in the stock intake manifold is preferrable, so I make these adapters. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/12/26 at 22:15:14 The adapter sleeve gets epoxied onto the carb. JB Weld works great. Now the assembly fits perfectly in the stock manifold. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/12/26 at 22:17:15 I stuck to my original jetting plan. Pilot Jet: 35 Main Jet: 140 Main Air Bleed: .039” Slide: #7 Slide Needle Clip: Center Groove Idle Mixture Screw: 1.5 Turns The float level adjustment seemed way too high, but the needle & seat didn’t leak so I left the level adjustment as-is. I’m not sure what’s up with this, normally the PWK float sits level (parallel with the gasket surface). |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/12/26 at 22:24:57 It started up OK, but not stellar. On the enricher, it was grossly rich. I had to close the enricher immediately. After a few minutes of warmup, I played with the idle speed and idle mixture until things were close enough to ride the bike. It was a bit rough but starting to shape up. It only took a few minutes to get it idling nice. The idle and throttle response were fine, essentially identical to the standard PWK knockoff. It was time to ride the beast. I put about 50 miles on it (normal riding, no WOT stuff). It ran very close to the original PWK. It was time to see how that main jet selection would work. WOT in 2nd gear was impossible. It ran perfectly up to 7/8 throttle but peg it and the engine would fall on its face. It would almost shut down at WOT. I was bamboozled. If it ran good at 7/8 throttle the main jet should be close. This was gross. I wasn’t sure which way to go (richer or leaner), but it’s always better to er on the safe side. I popped in a 150 main jet (4 sizes larger than the 140). Slightly better. OK, goin in the right direction. I popped in a 160 main jet (4 sizes larger than the 150). That was just about right. I was surprised. I figured that the smaller air bleed in this E-Tube carb would result in a smaller main jet compared to the standard PWK. That’s not the case. The E-Tube carb requires a significantly larger main jet. As I recall, that’s consistent with ThumperPaul’s experience. I think he ended up with a main jet somewhere around 162. With the 160 main jet, I could tell it was very close (possibly perfect). Timed runs showed it accelerated just about the same as the standard PWK. It was a wash; some pulls slightly faster, some pulls slightly slower, some pulls the same. I was out of jets. I had a 170 main jet, but this thing only needed a very small tweak (maybe a 158 or a 162). I ordered more jets, but I can already see there’s not much to be had here. I continued riding the bike for several hundred miles. It runs identical to the standard PWK except for the aforementioned enrichment problem and rapid fuel depletion when I shut off the petcock. Idle, throttle response, cruise, and acceleration are all identical to the standard PWK. It starts OK, but not as sweet as the standard PWK. Fuel consumption seems a bit higher, but I didn’t ride it long enough to do a fair comparison (I reached 100K on the odometer and it was time for the teardown). |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/12/26 at 22:26:18 Interesting Observations I already mentioned the grossly rich enrichment system. I don’t like that. I will be checking the enrichment air circuit and the enrichment jet. The high float position is kinda crazy. I use a shutdown routine like Dave. When I get close to home, I turn off the fuel petcock three blocks from my driveway. By the time I pull up to my garage the engine is starting to stumble a bit, so I know the float bowl is close to empty. With this E-Tube carb, it will barely run a block. It appears there is hardly any fuel in the float bowl. This baffles me. I might try making a special fitting for the float bowl drain so I can install a sight gage and see exactly where the fuel level is situated. The idle mixture screw ended up at ½ turn out. It idles just fine and there is no problem with afterfire or hesitation. Most folks wouldn’t even bother to pursue the mixture screw position since the carburetor operates perfectly at ½ turn. If you are a perfectionist, it would probably benefit from a 3/13/26 My bad, I should have stated that the idle mixture screw position could be improved a bit by installing a #6 slide and/or a #38 pilot jet. DBM |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/12/26 at 22:26:54 I popped the float bowl off the old PWK and checked the enrichment jet. It’s .014”. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/12/26 at 22:27:32 I also checked the enrichment air passage on the old PWK. It’s .229”. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/12/26 at 22:28:10 Then I checked the E-Tube carb. The E-Tube carb has a .035” enrichment jet. You can really get a sense of the difference if you compare this picture to the picture I posted of the old PWK enrichment jet. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/12/26 at 22:28:47 The enrichment air passage in the new E-Tube carb is smaller. It’s only .199”. So, the enrichment circuit on the new carb feeds way more fuel and less air. That explains the overly rich cold start. I think I might be able to fix that problem. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/12/26 at 22:30:03 This E-Tube carburetor is a good mixer. As it stands now, I prefer the original PWK knockoff, but the E-Tube unit runs great with only minor tweaking. I’m confident that I can iron out the few hiccups. I don’t think the overly rich starting circuit would bother most folks. I’m disappointed that I didn’t see a BIG improvement in acceleration, but I intend to keep at it and see if I can achieve at least a small improvement. I’m also gonna see if I can change that enricher jet to a .014”. That should be a fun project. If you order a PWK knockoff and end up with one of these E-Tube carbs, have no fear, it will run just fine. I hope some of you find this information useful. |
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Title: Re: PWK40 Knockoff with E-Tube Post by ThumperPaul on 03/13/26 at 06:02:01 As always, great write up and thanks for sharing! Aside from the enrichment circuit, it seems like this PWK40 with E-tube is a winner. Who is the seller? Does “E-tube” mean “enrichment tube”? Did it come with jumbo jets like the other PWKs we’ve tried? I swear they set these things up for a 250cc 2-stroke from the factory. OH! How do you rack up 100,000 miles in ~2+ years!! :o |
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Title: Re: PWK40 Knockoff with E-Tube Post by zevenenergie on 03/13/26 at 08:28:58 I enjoyed reading the topic. :) I won't get around to tuning my motorcycle anytime soon, but I think it's cool that all of this is in the available database. I am eager for a similar set of pin end gauges. I recently managed to buy a second-hand box of Swiss micrometers for smaller holes, but that only goes douwn to 6mm (0.236 inch (or 1/4"). http://https://i.imgur.com/ZgwvYbs.jpeg It is nicer to work when you can measure precisely. Sorry for the large photo. Imgur, where I host my photos, no longer has the function to post photos in any size. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/13/26 at 12:44:47 Hey Paul, how's the Honda? If you go back to the beginning of this post, you will see the specifics on the Amazon seller in reply #1. I noticed that on reply #31 you mentioned you were running a #40 pilot jet and a #145 main jet with good results. Do you recall if your PWK had an emulsion tube like the item I show in reply #8? Was that one of these E-Tube carbs? BTW, the "E" stands for emulsion tube, see reply #8. I thought the PWK you installed was one of these newer carbs with the emulsion tube, and I recall that in a different post I did on main air bleeds you mentioned running a #162 main jet. What am I missing? Hey Zevenenergie, how are you? That is a beautiful set of hole micrometers. I bet those cost a fortune. Are the graduations .01mm (.00039"). If so, Wow! What a nice set. They look like they would be perfect for measuring valve guides. Do you have one of these E-Tube carbs? What can you tell us about it? |
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Title: Re: PWK40 Knockoff with E-Tube Post by ThumperPaul on 03/13/26 at 13:35:41 Hey Mike. Sold the Honda and bought a Kawasaki Vulcan S 650. Love it. I can't remember the details. I did 2 bikes with the PWK. First was a PWK40 and I had problems jetting until I replaced the intake manifold with a Mikuni. The other was a PWK38, and I only remember it taking smaller jets than I would have thought. I can't remember - at least one of them had the removable emulsion tube (like a needle jet with holes???). |
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Title: Re: PWK40 Knockoff with E-Tube Post by zevenenergie on 03/13/26 at 13:42:42 Hi Mike, I'm fine, doing lots of divergent things.Thanks for asking. :) I don't have an E-carb. I'm still riding with standard carbs, which I've made a bit more aerodynamic on the inside. I was able to buy a whole set from 6 mm (1/4") to 60 mm (2.36 inch) from someone who closed down his business, at a very reasonable price. This Swiss brand is very expensive; the smaller ones cost $1,200 each if you have to buy them new, and the digital ones are completely unaffordable. They are accurate to within 0.001 mm (0.001 mm = 0.00003937[ch8243]). That,s 0,01mm per graduation.And there is a vernier scale on them that brings it to 0,001mm. I am often asked to repair worn bearing seats on 2-stroke engines, and that is what I bought them for, but they are also ideal for valve guides. Now that I have these micrometers, I have eliminated the measurement uncertainty,and because of that you can work much faster. |
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Title: Re: PWK40 Knockoff with E-Tube Post by ThumperPaul on 03/13/26 at 14:46:59 The PWK38 Air Striker had a non-removable needle jet (emulsion tube). |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/15/26 at 20:10:59 Paul, I can't believe you unloaded that beautiful Honda. Thanks for filling me in on the air striker. It doesn't actually have an emulsion tube. The air correction simply enters a passage that intersects the needle jet at the top, just below the venturi. Those carbs work great too. Zevenenergie, those are some amazingly precise instruments. Makes me feel like I've been working with a hammer and chisel all these years. Thanks for sharing. |
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Title: Re: PWK40 Knockoff with E-Tube Post by ThumperPaul on 03/16/26 at 05:40:46 You made me revisit what I did with the PWK40 I installed on “Red” in June 2023. It was a true 40mm (not a 38mm sold as 40mm). No “air stiker”. It DID have the “E-tube”. It used the stock air box with the panel air filter and a 2.5”ID tube to connect the carb to the stock air box. Jardine exhaust (stupid loud thing). No other mods (piston, cam, valves, etc). I think final jetting was #40 primary jet, #145 main jet, with the clip in the middle groove, and around 2 turns out on the mix screw. I probably could have gone down to a #38 primary jet. It ran ‘good enough’ for me and I was able to iron out the area between 7/8ths to WOT. Of the 4 roadworthy Savages/S40s I’ve owned, “Red” was probably the fastest. For the record, what all mods/upgrades are done on your bike? I guess I could reread all the “Evolution of a Hot Rod” stuff. Just thinking about context for this post about the carb tuning. |
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Title: Re: PWK40 Knockoff with E-Tube Post by DragBikeMike on 03/16/26 at 14:49:48 Thanks very much for the reference info Paul. I will hang onto it for future comparison. I just tore my bike down for inspection. Will be doing a report soon. I was running the following setup: 97mm flat top piston with 10cc pocket and .038" quench (10.6:1 CR) 40mm PWK (actually 38mm) DR650 cam Stage 3 head with 34mm intake valves Stock flywheel 4-Speed transmission with 5-Speed primary drive 23T front drive pulley Hybrid clutch with 13 plates and Barnett springs (Sneezy release cam) High speed oil pump drive with trans gear spray and oil cooler It ran great with this setup, but there were some problems lurking inside. I will fill you in when I do the report in a few days. |
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Title: Re: PWK40 Knockoff with E-Tube Post by ThumperPaul on 03/16/26 at 16:41:57 I’m staying tuned for your inspection report. |
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