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yz450scott

Jetting Problem

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I got a 2001 YZ426 and I am trying to fix a problem with my jetting I think. My bike runs great, starts find, but is running rich from what the plug looks like. It hesitates a lot from no throttle to 1/4 throttle. After that, all is good. I have dropped the needle on clip and leaned out the pilot let 2x. Which it is now a 38 pilot, 160 main, white brothers e-series pipe with stock head pipe..I am now thinking of leaning out the leak jet...Its a coincidence that I just removed my flywheel weight and rekluse clutch and my muffler broke and now I have jetting problems..I Had the muffler welded and repaired, but when reinstalling it. The exhaust gasket from the pipe to the headpipe fell apart. I put it together the best I could and probably going to buy a new one. Does anyone know if that exhaust gasket could make my bike run rich? Am I doing the right thing? ANyone please help, I am frustrated and have been tweaking my carb for the past 3 weeks...

One more thing, the intake boot going into the cylinder is tight but I can still twist the carb fairly easy..Will that affect jetting? Is it normal..

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let me ask you this firstly, when you checked the plug did you run the bike for a while to get everything up to temp, and checked it by running the bike wide open then killing it to read the plug in the right range?

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I got a 2001 YZ426 and I am trying to fix a problem with my jetting I think. My bike runs great, starts find, but is running rich from what the plug looks like. It hesitates a lot from no throttle to 1/4 throttle. After that, all is good. I have dropped the needle on clip and leaned out the pilot let 2x. Which it is now a 38 pilot, 160 main, white brothers e-series pipe with stock head pipe..I am now thinking of leaning out the leak jet...Its a coincidence that I just removed my flywheel weight and rekluse clutch and my muffler broke and now I have jetting problems..I Had the muffler welded and repaired, but when reinstalling it. The exhaust gasket from the pipe to the headpipe fell apart. I put it together the best I could and probably going to buy a new one. Does anyone know if that exhaust gasket could make my bike run rich? Am I doing the right thing? ANyone please help, I am frustrated and have been tweaking my carb for the past 3 weeks...

One more thing, the intake boot going into the cylinder is tight but I can still twist the carb fairly easy..Will that affect jetting? Is it normal..

A leak between the head pipe and muffler should not make too much difference in jetting, if anything it would make the bike run very slightly lean but probably not enough to make it stumble. Definitely get a new gasket in there.

No you should not be able to twist the carb easily. Check the rubber boots for cracks, and check the band clamps to make sure they are tight and not stripped. A leak in this area could cause the bike to run lean. A good test is to spray carb cleaner around these areas while the bike is idling, if the rpm changes (up or down) then you have a leak.

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