01 YZ426 wont start when hot

Im trying to fix a mates YZ so he can sell it, bike starts and runs OK when cold, as it gets hot it develops a bog off idle and will not start again if you stall it. You have to wait a good 30 minutes before it will start again.

Bike had new rings put in not to long ago but still doesnt have great compression.

Valve clearences are all in spec

It has stock jetting and has only developed the problem recently.

Anyone got any ideas?


Check your float level. If the petcock or anything between the tank and carb are clogged or gummed up, then the bowl will not fill fast enough. Sitting for 30 min would be enough for a trickle to fill the bowl. Clean the carb and use compressed air to blow out all the passages, fresh gas and give it a kick! I have heard of some using a bit of injector cleaner in a tank of gas as well. Good luck!

After cleaning your carb, I would check that your valve are not to tight and throw in a new plug.

The float level could also be high, which is frankly more likely in an older bike, and letting it sit 30 minutes would let it cool down to the point where it isn't so touchy about being slightly rich.

I would expect a float level low enough to cause problems with a hot start to cause problems underway as well, but either way, it's worth checking.

I know that everyone always says never to touch the throttle when hot starting a 426, but you might try opening it to somewhere between just off idle up to 1/4, HOLD IT STEADY (no twisting as you kick) and see how it reacts. My 450's will get slightly flooded now and then, and under those circumstances, they like a little more air coming in.

Well actually Greyracer, the only way to get it to fire when hot is to hold the throttle WIDE open, then the motor will catch and chug chug chug until it dies (all the while with the throttle full open)

I have a feeling I checked the float on it last time but Ill have another look


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