jml Posted June 18, 2016 Report Share Posted June 18, 2016 (edited) Hey all, I've had a similar issue with the bike blubbering on downhills on my Beta with a Keihin PW28 and now I'm having it on my 125 TXT Pro. I've stripped and cleaned the carb, made sure the jetting is correct for my riding locations and also adjusted the air mixture screw to around 2.5 turns out and I've got the floats level with the casting at around 18 mm when held at 45 degrees. Raising the idle seems to help and I've veried the RPM on the Hardline Tacho which is reading around 1,400-1,500 RPM (bike in neutral/flat surface) to stop it from blubbering on downhills... is this normal? Regards, Jason. Edited June 18, 2016 by jml Quote Link to comment Share on other sites More sharing options...
copemech Posted June 18, 2016 Report Share Posted June 18, 2016 (edited) floats do not go level on these carbs. Try this, I think it was closer to 21mm, but just use the casting as a guide. Edited June 18, 2016 by copemech Quote Link to comment Share on other sites More sharing options...
jml Posted June 18, 2016 Author Report Share Posted June 18, 2016 (edited) floats do not go level on these carbs. Try this, I think it was closer to 21mm, but just use the casting as a guide. Hey Copemech, This is how I was running it originally around 20.5 mm and inline with the casting mark under the jet holder. It didn't solve the problem, I believe this recommended is only to avoid overflowing of the carb on steep descents which results in reducing the amount of fuel lost out of the overflow pipe. This recommendation from splatshop is also a recommendation for their experiences with Sherco bikes which I believe have a slightly steeper carb angle compared to the Gas Gas. I've quickly superimposed the 2015 Sherco and Gas Gas bikes with equal sized dimensions and this seems to be the case. Edited June 18, 2016 by jml Quote Link to comment Share on other sites More sharing options...
lineaway Posted June 18, 2016 Report Share Posted June 18, 2016 The single vent PWK does not vent properly on downs and ups in a row. Look at Copes picture. By the choke is a blanked out vent. Use a 3mm drill and carefully drill it out. You can feel when you have gone through. 8-12mm. Worldtrialchamp had posted this mod several years ago. Quote Link to comment Share on other sites More sharing options...
copemech Posted June 18, 2016 Report Share Posted June 18, 2016 All stated is pretty much true in my thinking, and I also consider it a design limitation of the PWK. Add that a 125 may be more sensitive to the mixture fluxuations. The things to minimize it are few, that I am aware of. A good throttle blip on downhills helps keep things going, a little bump in idle speed. I also think the 28 is overcarbed for the 125, pity they do not do a 26. They meter well overall and make big power, but a Kiehin is quirky! 1 Quote Link to comment Share on other sites More sharing options...
jml Posted June 18, 2016 Author Report Share Posted June 18, 2016 The things to minimize it are few, that I am aware of. A good throttle blip on downhills helps keep things going, a little bump in idle speed. I also think the 28 is overcarbed for the 125, pity they do not do a 26. I think the bump in idle RPM is the way to go. Oh I also changed out the 52/125 jets for 45/120 and it just bogged really back on quick throttle bursts. It's back to normal while I figure out what to do! Quote Link to comment Share on other sites More sharing options...
lockie28 Posted June 18, 2016 Report Share Posted June 18, 2016 there is no proper way to measure the floats other than by eye! i wouldnt go tampering with drilling holes ect ect either , its normal for the idle to change on downhill runs .. just learn to put up with it, the keihin is a fiddly under engineered piece of kit if you ask me, im thinking of buying a OKO to replace my keihin carb. they will eventually drive you nuts! Quote Link to comment Share on other sites More sharing options...
jml Posted June 18, 2016 Author Report Share Posted June 18, 2016 im thinking of buying a OKO to replace my keihin carb. they will eventually drive you nuts! I was really close to doing the same, I've been reading many have had success with replacing the Keihin with an OKO to solve my problem. Quote Link to comment Share on other sites More sharing options...
heffergm Posted June 18, 2016 Report Share Posted June 18, 2016 Isn't an OKO a cheap Keihin knock off? 1 Quote Link to comment Share on other sites More sharing options...
lineaway Posted June 18, 2016 Report Share Posted June 18, 2016 https://www.youtube.com/watch?v=Q3cyFuemAXQ The tower that no gaskets are available is a terrible problem. Quote Link to comment Share on other sites More sharing options...
lockie28 Posted June 18, 2016 Report Share Posted June 18, 2016 Isn't an OKO a cheap Keihin knock off? Maybe yes!! but how many posts do you see regarding the Oko carb having the constant problems the keihin has? Quote Link to comment Share on other sites More sharing options...
lineaway Posted June 18, 2016 Report Share Posted June 18, 2016 My PWK has worked flawlessly ever since I added the second vent. Quote Link to comment Share on other sites More sharing options...
heffergm Posted June 18, 2016 Report Share Posted June 18, 2016 I have no keihin problems, so I can't really empathize. But I think what you're reading into this is a self selecting group. Nobody posts about how fine their keihin is, and almost nobody posts about OKO because there are hardly any of them. It makes no sense to me that a poorly cast copy of a keihin is inherently any better. 1 Quote Link to comment Share on other sites More sharing options...
worldtrialchamp Posted June 18, 2016 Report Share Posted June 18, 2016 The pilot circuit is easily blocked on the Keihin (and OKO). It still catches me out. Make sure you're cleaning it all in solvent as well as using compressed air reversed through all the circuits. Take the air/fuel screw out when cleaning. The PWK is a reliable carb but very temperamental if unclean. Another pitfall that catches many out is loss of the brass needle jet if you've unscrewed the emulsion tube.... The Factory spec for the float is 19mm on a Keihin. This setting is not the same for an OKO... Quote Link to comment Share on other sites More sharing options...
copemech Posted June 19, 2016 Report Share Posted June 19, 2016 My PWK has worked flawlessly ever since I added the second vent. I highly recommend this mod as well, regardless of all else. But I also remove the overflow tube, plug it, stops the p******. Makes the bowl easy to remove and install. I think the Beta PWK has the best idea with the verticle vent tube on the later ones. Add the second and go. Not sure how they got that? Quote Link to comment Share on other sites More sharing options...
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