Need help with 426

It's a 2001 model. Started having fouling plugs in the cold a bit. Recently, just put a new plug in and it started backfiring and wouldn't idle. I had to keep it about half throttle to keep it running and it was running way rough and holding it at half throttle steady, the rpm's would go up and down. It would also start backfiring and spitting. It is completely stock and was running fine up to this point. Also, the headpipe would get cherry red hot within a minute of starting it.

Almost looks like a timing problem, but for a bike that is just 6 months old? Maybe an adjustment on the carb i'm thinking. Any help greatly appreciated.


01' YZ-426

01' GSXR-1000

98' TLR-1000 racebike

A red header is normal, don't worry about that part.

If the carb and air filter is clean and you haven't fiddled with the jetting then the next step that I would do is check the valve clearances. I've seen many 4 strokes behave this way when the valves get overly tight. I don't promise that this is it, but if the bike has been ridden a good bit and they haven't been checked yet then it's about time to check them anyway.


There are a lot of things that could be causing this. Start with the simple stuff.

Do as SireThump says and check the valve clearances. It's an easy process.

Then check quality of spark and quality of fuel in the bowl.

Then from there it's going to get a bit more technical.

Do you do ANYTHING to this bike before this problem began?


I had similar problems with my '99 YZ400. I solved the idling problem by completely disassembling the carburator and cleaning it. I found a small piece of crud in the pilot jet that caused the bike to not idle. Be sure to blow all of the passages out with carb cleaner and compressed air. I still have a back firing problem when shutting the throttle off while decelerating. The problem doesn't show up until the engine is hot. I currently have the pilot screw turned out 1 3/8 turns, but I plan to back it out a little more to richen the fuel mixture up at small throttle. My next step is to re-check the valve clearance because I haven't done it for over a year. Hope that helps, and good luck!

Just went through the same thing on my 00426,120hrs on it. Valves tight. Cleared problems you described. :)

I just fixed my friends 2000 426 and it would not idle and was very hard to start. I disassembled the carb and cleaned it out, all problems resolved. It is not hard just be careful to keep everything clean.

I am going to check the carb tommorow night. Pull the bowl off and clean the jets. The bike is about 8 months old and the valves were never adjusted. I bet that is the problem. Does anyone have the specs for the valve adjustment clearances. Thanks for the responses.

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