doc_d Posted March 9, 2016 Report Share Posted March 9, 2016 (edited) I picked up a used 2014 250 Gas Gas a few months ago. I've only had it out for a serious ride once. It was surging, stumbling, hesitating and knocking pretty badly from just off idle to 1/4th throttle. I spent a few days jetting the bike but would like to know if anyone else had a similar issue with this throttle range? I cleaned the carb thoroughly. I sprayed WD40 around the base gasket, reed block, carb boot, etc to rule out an air leak. But it would be nice to know I'm not the only that had this issue with the stock carb setup. If I am the only one, while I might have fixed it buy fattening up the mixture in that range, but I really need to go back and figure out if I have another issue. If I'm not the only one, then I don't have to look any further than the jetting changes. Just in case I'm not the only one having the issue, hopefully this might help someone. I tried different pilot jets, needles, slides, etc and here is what runs the cleanest for me. First my bike was original setup like this: Main: 125 Pilot: 45 Needle: JJH Needle clip position: 3 (center) Slide: 3.5 Air screw: 1 turn out Here is what I ended up with: Main: 125 Pilot: 45 Needle: JJH Needle clip position: 4 (needle one position higher/clip one position lower) Slide: 3 Air screw: 1 turn out It seems to run significantly better in the just off idle to 1/4 throttle range. The slide made the largest improvement and fixed 90% of the issue leaving just the slightest stumble right at 1/4 throttle. Raising the needle cleaned that last little hesitation up. Doc Edited March 10, 2016 by doc_d Quote Link to comment Share on other sites More sharing options...
lineaway Posted March 10, 2016 Report Share Posted March 10, 2016 Try a 46 or 48 pilot. You never mentioned location, elevation or main jet. Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted March 10, 2016 Report Share Posted March 10, 2016 if in uk stick with 45. The 250 has always been an odd one as it never runs as sweet as the bigger bikes on the same carb and jetting, so much so that it came for years with a dellorto. Try boysen reeds use an inline filter and check float heights before changing much else. 1 Quote Link to comment Share on other sites More sharing options...
doc_d Posted March 10, 2016 Author Report Share Posted March 10, 2016 (edited) Sorry I left out the main jet. It has so little effect in the throttle range I was having an issue with I didn't mess with it at all. I editted my original post and added that info. I'm in Michigan. So I'm about 900 feet above sea level and normally it would be very cold here but we're having quite the heat wave. So the days I spent jetting the bike were around 62F/17C. I did try a 48 pilot. That alone made it about 10% better. But it was still surging and knocking and it was too rich at idle unless I really opened up the air screw. If I opened up the air screw to get the idle reasonably lean then I was back to the exact same amount of surging,knocking at partial throttle that I had with the 45 pilot. All my testing went as I expected with one exception. I put a JJG needle in which should have improved that area (off idle - 1/4 throttle) but it had the opposite effect. The knocking and surging was much worse. I'm having a hard time understanding that one. I need to go back and physically measure the needle against the JJH I had in there originally. My only explanation for that results is either maybe my supplier gave me needle not made by Keihin and the straight diameter isn't exactly right or perhaps when I installed it I got it caught up so it wasn't seated correctly. Because I know I was lean in that throttle range and the JJG should have definitely richened it up or in the worse case scenario had no impact in that throttle range. Doc Edited March 10, 2016 by doc_d Quote Link to comment Share on other sites More sharing options...
lineaway Posted March 11, 2016 Report Share Posted March 11, 2016 (edited) So which slide was used with the 48 pilot? By the way float height is very critical with this carb. Edited March 11, 2016 by lineaway Quote Link to comment Share on other sites More sharing options...
doc_d Posted March 12, 2016 Author Report Share Posted March 12, 2016 I tried the 48 pilot with the #3 slide. I didn't check the float height, that's a good call. I need to do that. Quote Link to comment Share on other sites More sharing options...
lineaway Posted March 17, 2016 Report Share Posted March 17, 2016 Would not hurt to try the 48 with the 3.5 slide. Our fuel is much different than the UK. Quote Link to comment Share on other sites More sharing options...
doc_d Posted March 17, 2016 Author Report Share Posted March 17, 2016 When the temps get above 70F I might put the #3.5 slide back in and see how it runs. If it's still lean I can give the 48 pilot a go. My trials club got together last weekend for a little practice and I ran the bike for about 4 hours. It ran great and never missed a beat with the #3 slide and needle lifted 1 position. Quote Link to comment Share on other sites More sharing options...
heffergm Posted March 17, 2016 Report Share Posted March 17, 2016 (edited) FWIW, I just bought a GG as well (2014). I was told by the dealer to run it on a mix of race gas and pump gas, specifically because the GG will run very poorly on straight pump gas. Before you go crazy trying to jet it, you might want to give that a try and see if it runs better. Edited March 17, 2016 by heffergm Quote Link to comment Share on other sites More sharing options...
doc_d Posted March 18, 2016 Author Report Share Posted March 18, 2016 (edited) FWIW, I just bought a GG as well (2014). I was told by the dealer to run it on a mix of race gas and pump gas, specifically because the GG will run very poorly on straight pump gas. Before you go crazy trying to jet it, you might want to give that a try and see if it runs better. For what it's worth the guy I bought it from said he ran it on 50/50 race gas/pump gas and it was still way too lean in the idle - 1/4 throttle range with the gas he left in the tank. Where are you at? What elevation and weather conditions? How's you're bike run in the 0-1/4 throttle range? I ask because I'm worried that I have another issue I'm missing because I'd be very surprised if it was delivered it that lean from the factory. Edited March 18, 2016 by doc_d Quote Link to comment Share on other sites More sharing options...
lineaway Posted March 18, 2016 Report Share Posted March 18, 2016 Also the blanked out vent by the petcock can be drilled out. Makes a big difference on stalling while riding steps. One vent is not enough, the PWK for mx has six vents. Quote Link to comment Share on other sites More sharing options...
heffergm Posted March 18, 2016 Report Share Posted March 18, 2016 For what it's worth the guy I bought it from said he ran it on 50/50 race gas/pump gas and it was still way too lean in the idle - 1/4 throttle range with the gas he left in the tank. Where are you at? What elevation and weather conditions? How's you're bike run in the 0-1/4 throttle range? I ask because I'm worried that I have another issue I'm missing because I'd be very surprised if it was delivered it that lean from the factory. I'm at sea level, weather in the 50-60F range when I ride currently. Bike runs great. Jetting is stock. Quote Link to comment Share on other sites More sharing options...
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