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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Keihin PWK38 Air Striker Carburetor Installation /cgi-bin/YaBB.pl?num=1714330191 Message started by ThumperPaul on 04/28/24 at 11:49:50 |
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Title: Keihin PWK38 Air Striker Carburetor Installation Post by ThumperPaul on 04/28/24 at 11:49:50 Taking a page out of DragBikeMike's playbook I will be installing a PWK38mm Air Striker Carb. I was going to do this mod later with some other mods, but I destroyed the air/fuel mixture screw on my stock carb, so here we go. A couple years ago with Mike's help, I installed a PWK40 on a S40 I had at the time. It worked well, but in the end I would say it was too big, needed bigger jets, and I probably wasn't feeding it enough air (stock air box and flat panel filter), and pretty open Jardine exhaust. I bought this carb on Amazon from JFG Racing for $36. It's pretty nice. I'm not sure what to think... For the price, it should be a knock-off, but it's plastered with Keihin and Sudco... I wonder if they bought these from Keihin as some "2nd quality" wholesale. Link ---> https://www.amazon.com/dp/B07MMJV6BT?ref=ppx_yo2ov_dt_b_product_details&th=1 More pics and comments/steps coming. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 11:50:58 Off Road Use Only (hehe)... Made in Japan. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 11:57:59 Air Striker View. The air striker flow channels supposedly concentrate air flow over the main fuel curcuit to increase low end throttle response. Even without the air striker feature, these semi-flat oval slide carbs provide superior throttle response. No waiting for vacuum to lift the diaphram like in the stock CV style carb. It's actially the best part of these slide carbs in my opinion. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:03:56 Left side view. The idle screw is metal and not cheap plastic like some of the carbs you'll see on Amazon or E.Bay. Note the Keihin stamp and lots of QC green and blue mark-ups. The Air/Fuel Mix screw is "upwind" on the air box side of the carb bore. It meters "air" - turning it counterclockwise is leaner. This is the opposite of the stock CV carb that meters "fuel" on the engine side of the carb bore. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:10:25 Right Side View. There are 4 vent tubes. The top 2 vent tubes are functional float bowl vents. The other 2 below those are not drilled through. For some "quad vent" applications like on 2-stroke dirt bikes, these get used somehow. I'm not up to speed exactly how that works. (Crash the dirt bike and it has 4 vent tubes to pee out of??) |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:11:19 A nice smooth 38mm bore. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:17:38 Air intake side has 63mm OD and about 57mm ID. The 2.5" ID "turbo tube" fits nicely. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:19:01 The slide, needle, and spring setup. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:21:02 Test fit of the throttle cable ferrule in the slide catch contraption. This will test your patience putting it together. This is a test fit outside of the slide before trying to insert the cable ferrule in the contraption while inside the slide. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:24:39 I'm using a custom cable I already had extra laying around from my last S40 that had a Mikuni VM36 slide carb. I think it will work without modifing. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:29:45 It came setup with a #170 main jet and #50 pilot jet. Using DBM's setup for his bike as a guide , I have installed a #138 Main and #35 Pilot, with e-clip in the 4th groove down on the needle. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:31:41 With the Main Jet removed, you can see it has a Non-Removable Jet needle. If it's removable, I'm not messing with it. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:33:48 It has a float bowl plug. You could theoretically change the main jet without removing the entire float bowl. Note: I swapped out the float bowl JIS screws for M4-0.7x16mm stainless steel allen head screws. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:39:36 A test measure of the throttle cable exposed length. It looks like it will have enough exposed cable at the throttle tube end of the cable. I should measure it, but not today. We'll see. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 12:43:13 The silicone "turbo tube" I will use to connect to the air bix. It's 2.5" ID and 8" long. I will cut to length (like 5.25" - 5.5"). Check out those monster t-bolt clamps that came with it. Those will probably need to get swapped out for some narrower worm gear clamps. The 2.5" ID makes a really nice fit even before clamping. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 15:09:15 Here's a link to DragBikeMike's "Evolution of a Hot Rod Part 4". My inspiration for this carb mod. This is where Mike goes into detail on setting up the PWK38 he installed on an almost stock bike. http://suzukisavage.com/cgi-bin/YaBB.pl?num=1625732492/15 Mike achieved the best performance with a #35 Pilot Jet, #142 Main Jet, with the e-clip in the 4th groove from top on the needle (1 groove richer than the 'neutral #3' groove in the middle). To get the best performance out of his bike with the PWK38, Mike installed a K&N cylindrical filter in a highly modified airbox. The K&N RD-0710 is 3.5” diameter by 5” long which has over twice the area of the flat-panel filter. Mike's other nonstock item is his muffler (LCGP 2.5” resonator with baffle). I'm installed the PWK38 Air Striker with a #35 Pilot, #138 Main with e-clip in the 4th groove from top (richer). I'm starting here and trying this setup with a stock air box (side cover removed), flat panel Hiflofiltro air filter, and stock header/muffler. I think I’ll be fine with the #35 Pilot (like DBM’s). I’m mostly wondering about my selection of a #138 main. This is 2 sizes down from DBM’s #142 with his better flowing air intake and muffler. The impact of the “air striker” feature is a bit of a flyer and unknown to me in terms of jetting adjustments. Gotta start somewhere… Thoughts? Hoping DBM and others that have installed the standard PWK38 or PWK38 Air Striker can chime in with thoughts/suggests. I'm considering a bigger better flowing K&N or Uni foam pod air filter either now or down the road. I'm also planning on a dyna muffler in the future. My main goal right now is to get the bike running again and then I can tinker as needed and do more mods later. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/28/24 at 17:55:25 And not to be forgotten, a good intake manifold is needed. The stock manifold with a built-in O-ring ridge doesn't fit snuggly enough on the PWK. This Mikuni intake manifold is what allowed me to finally get the PWK40 I installed on a different S40 dialed in correctly albeit still a little rich. The Mikuni manifold eliminated air/vacuum leaks that were causing me to chase my tail setting incorrectly compensating up with huge jets and getting terrible gas mileage. With a tight fit on the manifold, I was able to install more appropriate smaller jets and get a good setup and performance. Mikuni HSR42 Carburetor Rubber Flange Adapter 70mm-75mm 45mm Spigot HS42/018-42K |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by DragBikeMike on 04/29/24 at 11:40:09 Looks like you are comin at this the right way. Jetting should be on the rich side. That's good. Start rich, it's always safer. You should have additional main jets on hand (135, 132, & 130). I have found the #35 pilot a bit rich. I believe the #35 is the smallest pilot jet available from Jets-R-Us or OEM. There are some cheap jet kits on Amazon that include a #32, but the main jets provided in those cheap kits are a bit funky. The sketchy kits are so cheap that I bought one just to try the #32 pilot. The #32 pilot measured out correctly (lucky me) and it cleaned up the idle a bit. I use the funky main jets for other projects. Sorry to hear about your stock carburetor. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 04/29/24 at 13:35:25 Thanks Mike. Interesting that you think the 138 will be too rich. I thought 2 sizes down compared to your bike would be about right. We’ll see. Haha! I am the proud owner of some of those cheap Amazon jets. I know I have 32 pilot and 135 main. I need to see if I have the other smaller main jets. Do you know what effect the Air Striker will have on jetting? Would it allow for use of a smaller main jet or leaner needle setup? Or is it the opposite? |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/03/24 at 06:45:35 The exposed length of throttle cable is too much. This pic is with the adjuster at the carb fully extended (about 1/2"). The exposed length is about .75 - 1.0" too long to get the throttle end adjuster somewhere closer to the middle of the range. I'm using the stock throttle tube and even if I hacksawed it to use the second hole (designed for a return cable) on the throttle tube, it would stll be too much cable to set up the freeplay correctly. This cable is from Murray's Carbs. He offers this cable with the Mikuni VM36 carbs he sets up and sells for the Savage. He swears its the right length, but admits mistakes happen. He ended up sending me a shorter exposed length cable after some lengthy back and forth, and I used that cable on a different bike (Woody) and it was good. So, I'm trying to use this extra backup cable on my new project. I'm going to cut the cable about .75" and solder on a new ferrule. If I don't like or trust my soldering work, I'll be getting a new cable. It wouldn't be right if everything went perfectly smoothly for me. EDIT: I decided not to solder. I decided to use a screw type “emergency” ferrule on the throttle tube end of the cable. It holds very well when I try to make it fail. I ended up shortening the exposed cable 1” and I still had about 3/8th inch that needed adjusting out to get the free play right. Now that I have the length right, I may go back and reinforce the screw-type ferrule with a little solder. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by DragBikeMike on 05/03/24 at 20:54:23 I'm lookin forward to lightoff. I really like the PWK. It's been a great carb for me and it's very easy to dial in. It will be interesting to hear how it runs with that stock muffler, where your jetting ends up, how the air filter works, etc. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/04/24 at 06:18:57 Thanks Mike! Me too. I’m installing a new stator this morning and with some luck I might be able to get her fired up later today. Your need to install a K&N air filter to get the best performance has me thinking. As an aside, I scored a pair of nice HD Dyna mufflers on E.Bay. Once I have this bike running well again and any other issues addressed, my next phase will probably be the dyna muffler and air filter. Trying hard not to get the cart too far out in front of the horse. If I hadn’t destroyed the stock carb, I wouldn’t be installing the PWK right now. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/06/24 at 05:05:08 Hey Mike. I was able to get my first start-up yesterday after needing to bypass the clutch position safety sensor. I haven’t test ridden it yet, but after getting the bike reasonably warmed up in the garage, I was able to somewhat assess the air/fuel mixture at idle/pilot jet. Bike fired right up at 2 turns out on the 35 pilot jet. After warming up, I found the best mix at 2.5 turn out (adjusting leaner). I can see how you decided to go down to a 32 pilot jet and the 35 is a bit rich. A few modest rolls on the throttle suggest I may need to lean-out (too rich) the needle jet by 1 grove. I need to test ride it first to get a real idea. I have the e-clip is in the 4th groove down from the top and I may need to move it up to the middle groove. And the main jet is obviously a TBD. But it seems right now that you are all around correct that my initial jetting is a bit rich. Generally speaking it’s close and ridable. Some test riding today. Side Note: I was able to clean up the clutch position safety sensor and it’s working. What I don’t understand is after I’ve pulled the clutch lever to push the pin and close the circuit, how does the bike stay running once the clutch is released and the pin compresses and opens the circuit again? Is this purely a safety start circuit of the wiring? The other S40s I had didn’t require pulling the clutch while in neutral to start. Were those bikes already modded to bypass the switch? I never checked it on the other bikes and I just assumed it didn’t need to have the clutch lever pulled to start while in neutral. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/06/24 at 11:18:48 First test ride update.. Running Rich... The 35 pilot jet was best at 2.5 turns out on the A/F mix screw. A 32 pilot jet will probably be better at something around 1 turn out. The 35 is livable and idle is steady. Mid-range on the needle 4th groove is a little rich. Could be crisper. May move the clip to the middle groove (a notch leaner). I want to try a smaller main jet to see if it also helps in the mid-range. WOT is RICH. Starting around 3/4 to full throttle, it will bog. I need to either get more air flow and/or try a 135 main or possibly a 132 main. My goal here is I want to identify the right jetting for a stock bike using a PWK38 Air Striker. I want this knowledge. Once I scratch this itch, I'll be moving forward to doing some modifications. Otherwise, everything else was good. Neutral to 1st gear is a little cranky - stubborn to go into 1st gear - took 2-3 bumps on a few occasions. Sometimes it dropped in like butter. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by DragBikeMike on 05/06/24 at 11:22:45 "What I don’t understand is after I’ve pulled the clutch lever to push the pin and close the circuit, how does the bike stay running once the clutch is released and the pin compresses and opens the circuit again?" The clutch switch controls voltage to the decompression relay, not the ignition system. So, the ignition system doesn't care if the clutch switch is open or closed. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by DragBikeMike on 05/06/24 at 11:28:16 Regarding the jetting, only change one thing at a time. Your post sounds like you are fixin to drop the needle and change the main jet all one crack. You may end up goin back & forth a few times but it will be a better process and you will understand the carb better. Change one thing, try it, then move on. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/06/24 at 11:29:15 Thanks Mike. This is much easier to understand than me trying to read a spaghetti wiring diagram! |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/07/24 at 05:57:23 It’s not definitive yet, but generally speaking the Air Striker carb wants smaller jets to dial-in compared to a non-air-striker carb. I swapped the 35 pilot jet to a 32. This is favorable. The 32 makes the idle speed screw adjustment much more responsive to changes. A 1/8th turn of idle speed screw actually adjusts the idle speed. With the 35, it took almost 1/2 turn to impact the idle speed. I think I’m about 2 turns out on the air/fuel mix screw with the 32. I was at 2.5 turns out on the 35. I’m happy with the 32 and will call this Done aside from maybe a little fiddling with the A/F mix screw a bit.. Swapped out the 138 Main for a 135. This didn’t achieve much to reduce the overly-rich condition and bog at 3/4-WOT. I’m going to try a 130 next. I didn’t move the e-clip from 4th groove from top to the middle groove on the needle yet. It seems like this will be a necessary adjustment to get the mid-range dialed in. But I want to get the main jet dialed in first to see what impact it will have when the needle is metering a smaller main jet. The midrange may mostly correct itself with a smaller main jet. Maybe, but saving the midrange adjustment for last (if I have to move the e-clip up a groove or not). Getting closer. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/13/24 at 07:38:43 Update. Today’s test iteration was 32 pilot, 135 main, and e-clip moved up to the middle groove (1 groove leaner than the 4th groove I had it in last try). The change this go ‘round is the e-clip position on the needle. Much better, but I still have a rich bog in the upper end of the midrange and WOT (3/4 throttle to WOT). The low end of the midrange seems pretty good. Next up is trying a 130 main. I’m thinking this should alleviate the upper end rich bog without impacting the low midrange unfavorably. We’ll see. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/13/24 at 09:14:14 Latest iteration has it close, but still not 100%. 32 pilot, 130 main, e-clip in middle groove. The 130 main improved things somewhat. It’s getting a bit perplexing now. It’s almost intermittent now at the upper end 3/4-WOT. I can kinda sneak up on WOT gently, but rolling on it hard will cause a stutter/bog and you can hear the richness. The harder I roll on it, the more likely it is to bog. I can’t decide if I should try a 128 main or move the e-clip up another groove. The 128 seems small, but this air striker carb has a unique mind of its own (maybe this is the right next move). But is a change from a 130 to 128 enough to make a real difference? Should I try a 125? Moving the e-clip up another groove concerns me that it could become too lean in the lower midrange. Changing to a smaller main jet seems safer and will also slightly lean out the midrange (smaller main jet that the needle has to meter in the midrange). Maybe a different needle with a more gradual taper is in order. Thinking out loud here…. Cruising is smooth with ample throttle response and roll on power in the midrange. It’s very rideable as long as I don’t try to hot rod it. But I want the capablity to hot rod it! lol. Thoughts/suggestions anyone? I’ve been through 6 iterations now. Is the 7th time the charm? What’s it going to be…. Side note: Nibbi sells a PWK38 Air Striker seemingly jetted for 4-strokes. They include a 35 pilot and 3 main jets 130, 132, and 138. To me, this tells me I’m in the right ballpark. Other sellers of this PWKs have them shipped out with huge jets that imply a 2-stroke dirt bike setup (like this one came with a 55 pilot and 170 main!). |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/13/24 at 12:00:22 I decided to try the 125 main. It’s installed, but the test ride will have to wait until tomorrow. Thunderstorms rolling through this afternoon. Fingers crossed. Still want to hear any ideas! My thought process was that the 125 won’t create a dangerously lean condition up top and will be more definitive and pronounced change than the 128 main. If it cures the rich bog, it will leave me wondering if the 128 would be better. Let’s see what the 125 does. Right now 32 pilot (1.75 - 2 turns out), 125 main, e-clip in middle groove. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/13/24 at 13:49:38 DBM, if your reading - When you tuned your PWK38, you mentioned needing needle "N427-48-EEN/017-455". I'm thinking I might need this needle too. When I'm on the JetsRUs page for the N427-48, they don't list the EEN/017-455. They have an EEM/017-454. Link below. The needle in my carb is totally unmarked, so I don't even know what my baseline starting point is. According the the Keihin carb parts page, the standard stock jets are 170, 55 and Needle 48-DDJ for the PWK38 Air Striker. Since my carb came with the 170 and 55, it might be reasonable to assume the needle is a 48-DDJ. (You thought the needle that came with your carb might be an ECN.) I'm struggling to make sense of all the tables and charts on the JetsRUs page. Codified alpha-numeric soup. Was your decision for the EEN based on "more taper, but longer and larger diameter" for a leaner more progressive needle and then use the 4th clip groove to adjust it richer. Where I'm at right now (before testing the 125 main), it feels like the fuel mixture is about right in the low midrange and then goes rich in the upper midrange with the e-clip in the middle groove. I'm trying to think through what taper, length, and diameter relative to the 48-DDJ would correct it. Heck, maybe I just need a better flowing air filter setup and this stock setup with the air box cover removed just isn't cutting it. But I stubbornly believe I should be able to make it work better. https://www.jetsrus.com/a_jets_by_carburetor_type/needle_keihin_N427-48.html |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by Fast 650 on 05/13/24 at 21:16:35 The stock flat panel filter can't flow enough to keep up with the air striker. You will need to modify your airbox to fit a cylindrical filter as DBM found out. Details are in this thread: https://suzukisavage.com/cgi-bin/YaBB.pl?num=1625732492/15 |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by DragBikeMike on 05/14/24 at 02:48:51 First, figuring out exactly what genuine Keihin needle is equivalent to the knock-off needle is a tough job. Even if you have a micrometer with a vernier, it is still very difficult. You have to take measurements accurate to within four decimal places and then calculate the angle to within 15 minutes. It's a crap shoot. I can't recall what motivated me to switch to the EEN needle on the 38PWK Air Striker, and I can't find my measurements on the knock-off needle. I do have a few measurements on other needles that you may find useful. Remember, only change one thing at a time. You will get lost if you start changing two or three things at once. I suggest you concentrate on your main jet. Once you get it to run clean at WOT, then fiddle around with the slide needle. I've been down this road with you before. The main air bleed is important. It has a huge impact on your main jet. When I set up the 38 Air Striker, I didn't measure the main air bleed, so we have no way to compare my setup with yours, and you have a stock muffler which is super restrictive. I wouldn't worry too much about your air filter at this point since the muffler has the whole system stopped up. You should be able to get it dialed in with the setup you have now (open air box, stock muffler), and it should require a lot less fuel than mine required. For reference, a Mikuni VM runs pretty good on a savage with main jets in the 190 - 210 range. The orifice size in the Mikuni 190-210 jets is equivalent to the Keihin 125-132 jets. But you always must be mindful of the main air bleed. Generally, the Mikuni's main air bleed is pretty small in comparison to the PWK, but we don't know what size your air bleed is. We also don't know what size your needle jet is. You say you have it running decent at idle and part throttle, so I suggest you dial in the main jet and then see how it runs part throttle. If the low speed ops is good, and WOT is good, then you can dial in the needle. If there isn't sufficient range of adjustment on your needle, then you will need to select an appropriate needle. Here are some needle measurements for you to chew on. I'm currently running an EGK and it runs very good, but I have a lot more motor than you do. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by DragBikeMike on 05/14/24 at 02:59:33 This is a comparison of main jets in the range you are working with. I found that the orifice size on the PWK usually ended up being pretty close to the orifice size that gave best performance when I was running the Mikuniu VM. Seems logical, they are almost identical mixers at WOT. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/14/24 at 04:56:43 Thanks Mike. Yes, you’ve helped me down this path before. Thanks once again! I’ll give the 125 main a test run today and report back. Hopefully it does the trick. Changing needles does seem like a crap shoot not exactly knowing what I have right now, and I don’t have the gauges to measure it. I was trying not to rely on jet comparisons to the Mikuni VM36. The 200 main jet worked well on Woody with the same air box setup and open turnout exhaust. If the VM36 and PKW38 are comparable at WOT and main air bleed size, the 125 may still be too big on this bike with stock exhaust. I may end up at a 120. The good news is that performance is improving with each change I make. I’m going the right direction. And yes, I’m doing 1 change at a time now. It was only the first rejet that I made 2 changes at the same time when it was very clear I was too rich all around. Like you said, safer to start too rich. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/14/24 at 05:30:13 Fast650 - I acknowledged Mike’s work at the beginning of this thread. I’ve read it multiple times and Mike’s helped me tune a PWK40 previously. My goal here is to see what jetting works for a totally stock bike except with the air box cover removed. I want to know. Down the road, I’ll do some mods and have the joy of retuning all over again. Dyna muffler, Uni foam pod air filter, and maybe a mild Webcam 466 (courtesy of Dave). Of course, a Versey cam chain tensioner and Sneeze clutch cam are on the list too. Think about all this more later. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by Fast 650 on 05/14/24 at 08:17:20 467A677F6277604273677E120 wrote:
I think you missed what I was getting at. You can get it to work with the stock filter and the door removed, but performance takes a big hit. It is over a second slower than the stock BS40 with that setup. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/14/24 at 09:58:04 4F687A7D3F3C39090 wrote:
I think you missed what I was getting at. You can get it to work with the stock filter and the door removed, but performance takes a big hit. It is over a second slower than the stock BS40 with that setup. [/quote] Gotcha. I was planning on installing the PWK38 with other mods later (pod filter and exhaust for better flow), BUT in the process of rebuilding the stock BS40 carb, I destroyed the air/fuel mixture screw and carb body around it. So, here I am now installing the PWK38 to get the bike running. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/14/24 at 10:05:55 Update: The 125 main is very close, but still a tad too rich. Next up is a 120 main. I'd try a 122 main but I don't have one handy. And as an aside, for some reason, the carb decided to flood out the float bowl overflow tube. Either a bad float needle valve or the float level is set too high. This hasn't happened until today when I was finally able to get some real WOT pulls in 3rd/4th/5th gear. Time to do some checking. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by DragBikeMike on 05/14/24 at 17:37:27 I believe the Sneeze bought one of these knockoffs and a float broke off the float arm before he ever tried to run it. I suspect you will need to remove the float bowl. Let us know what you find in there. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/14/24 at 18:52:30 Thanks for the history on Sneeze’s experience, Mike. Today was busy with title transfer this afternoon. I plan the remove the carb and pull the bowl tomorrow. I’ve been doing these main jet changes and e-clip changes without removing the carb which has been convenient. Unrelated, but what size fuel line are you using? The 5/16th is pretty loose and must be clamped really well at the nipple. I’m thinking 1/4” would be fine on this gravity fed slide carb (it definitely fits better on the nipple). I’m thinking 1/4” fuel line should provide more than enough flow for the float needle valve bore to handle (sucking through a straw). I’ve read that the stock CV carb when set on run (vacuum mode) instead of prime on the stock petcock valve really kinda needs the 5/16th fuel line to get the right vacuum and flow. I never experimented with that with a smaller 1/4” line and always used 5/16” line with the stock petcock valve and carb. I’m using a cheap “Raptor-like” petcock valve with 8mm (call it 5/16th”) nipple. It can accept the 1/4” or 5/16th” fuel line. I’ll eventually upgrade the petcock valve, but this is how I roll when I’m seeing if I can get an old barn find Savage running again. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/15/24 at 11:42:07 Photos trying to find the reason for flooding float bowl. I can't exactly put my finger on it, but I adjusted the float level about 2mm lower and the flooding stopped. There were tiny tiny bits of crud in the bowl - maybe that was it. I thought I cleaned the fuel tank well and replaced the fuel lines as well. The float bowl and float needle valve and assembly/passage got a quick squirt down with carb cleaner. 1st Photo - getting the carb out without removing the battery box or air intake "turbo tube". It was like a 3-hand wrestling match, but I got it in and out on the left side. The turbo tube is new and stiff as a board (offers good rear support for the carb though). |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/15/24 at 11:43:23 Floats float and structurally look good. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/15/24 at 11:45:53 If there is a way to remove the float needle valve assembly housing, I couldn't figure it out. And I have no idea if there is a small filter/screen down in the passage. I couldn't see it if its hiding down in there. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/15/24 at 11:46:52 Float needle valve looked brand new as it should. It's not the problem... |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/15/24 at 12:00:59 Made some reference marks to get float height measurements. First mark is 7mm (6.5mm is spec for an authentic short body pwk38) and 16mm is the other mark (16mm is spec for an authentic long body pwk38). Who knows what the spec is for this knockoff pwk. But, this knockoff PWK must be a long body because there was no way it was going to line up with 7mm. (And yes, I know my lines aren't perfectly straight - close enough!) My best eyeballing guessimate is the float was set at about 14mm BEFORE I adjusted it to about 16mm. I don't have fancy tools to hold the carb exactly at a 60 degree angle and measure the angle with a protractor. Good ole fiddling back and forth eyeballing the clip and float needle valve as I played with it. I knew I wanted to lower the floats 'some', so I just went 'some' in that direction. I think I move it down about 2mm. Hey, the overflow leak stopped and the bike didn't starve for fuel under WOT or regular riding. I must have done something right! Right?! |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/15/24 at 12:04:14 Best photo I could get trying to manage the carb in one hand and phone camera in the other. The float height is set to about 16mm. It looked better in person without a phone in my hand and I was fiddling around with it. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/15/24 at 12:05:09 Another view fumbling around with it trying to simulate a 60 degree angle. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/15/24 at 12:07:33 The clip position after adjustment. The photo before adjustment is crappy. Real technical - I bent it down a little bit. |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 05/15/24 at 12:22:01 And the good news is, I’m 95% happy with the carb jetting/tune. I need some more saddle time testing and MPG testing. Pilot Jet: 32 (2 turn out on A/F mix screw) Main Jet: 120 Needle: e-clip middle groove I might be sensing a little leanness at WOT. I may need to try a 122 main. The needle e-clip might need to go up 1 groove (leaner). Kinda scared to try this change. Love the 32 pilot jet setting (easy start, smooth idle, good transition). I need some more butt dyno testing, but it’s very satisfactory for everyday cruising. I’d consider this a good starting point for anyone considering a PWK38 Air Striker carb for a stock motor with stock exhaust, stock air box with airbox side cover removed. (At steamy hot sea level like Houston.) |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 06/18/24 at 05:30:57 Latest update. I installed a UNI 4” pod foam filter directly to the carb (no snorkel tube or air box chop job). Pilot/idle circuit = still great with the #32 jet. Only needed to turn the a/f mix screw about 1/4 turn richer. It’s about 1-3/4 turns out now. Midrange feels pretty good, maybe a tad rich with the e-clip in the middle groove still. WOT - While the midrange can find a fairly happy place with a 120, 122, and 125 - I’m struggling a bit to get a nice clean WOT response with the UNI filter installed. The #120 seemed lean. The #125 seemed a little rich. Bought a #122 and I’m perplexed with it. I can’t tell if it’s too small (lean) or too big (rich). It can act “clean” sometimes. If I sneeke up on WOT, it’s generally okay. If I roll on the throttle hard when I think I’m at a good rpm level, it just isn’t clean. It actually backfired out the stock exhaust rather loudly (haven’t heard a bang like that before through the stock exhaust). I’m coming to the conclusion that I need to install the Harley dyna muffler to open things up and get WOT to feel right. Thinking the stock muffler is just too restrictive with the PWK38 and UNI filter. Thoughts? I wish I could describe the performance feel better. It’s just not always “clean” - like it’s lean sometimes and rich other times. I got the boomer backfire when I was hammering it pretty hard in 2nd. I can creep up to WOT in 4th pretty cleanly. Hit 84mph in 4th getting on it last week. The UNI filter does sound cool when you can hear the air induction! |
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Title: Re: Keihin PWK38 Air Striker Carburetor Installati Post by ThumperPaul on 06/24/24 at 07:57:08 I’m at the point where I think it might be constipated by the restrictive stock muffler. I got a kaboom on decel in 4th gear when I rolled off from WOT. In 2nd gear, it cuts out when I roll on it hard. I’m going to bump up to #128 main jet. When I went down from a 125 to a 122, I think I may have misdiagnosed and went the wrong direction. Trying the 128 should tell me something. I did get 53mpg on a 60 mile ride on Saturday cruising mostly 60-65mph out in the rural backcountry without riding like a yahoo. Bike generally runs great and getting decent MPG, but I want to be able to romp on it without getting the hiccups. I’m at a place where I can’t tell if I’m a tad too lean or too rich at WOT. And still wondering if it’s a bit rich on the needle in the mid-range or ‘just right’. A dyno test to see the air fuel mixture across the power band would be great. But the one place I’ve found that can do a dyno on the Savage is majorly backed-up and kinda expensive. So I’m stuck with the butt dyno. |
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