NEED HELP!!!! 02 YZ426 keeps quiting at high rpm????

The problem is your going high rpm's. The air is moveing incrediably fast. Then your slamming the throttle shut. Which causes the air to slow down drasticly. So your running way, way, way, way to rich. The gas is going into the motor and flooding it. The popping is the gass in the exhaust exploding and being burned off do to the heat. There is so much gas that you cant burn it all so it's going into the exhaust and your plug is ending up that way. You need to get spec's. Put it all back to stock jets and go from there. Your accelerator pump might be malfunctioning to. Check the overflow hoses on the carb. If one is blocked it will cause this. Check to make sure that the valve that lets gas into the bowel seal's propperly. Make sure your floats are adjusted right. The reason why the rpms increas when you pull the hot start is because it leans out the mix. Hope this helps let me know.

Thanks for the info. It has all the stock jets in it. 162 main. The floats are set right and everything seems to be right. What i dont get is that it was running great a couple of weeks ago and now this. I'll check the over flow lines to make sure they're not plugged. Thanks again

carb overflows are ok, nothing blocked. :thumbsup:

After reading thru all of that I am begining to wonder if its not electrical. I dont know much about the electrical inners of these bikes so dont quote me on that. But maybe a CDI or Stator problem. Ya know someone else that has a 426 that maybe you could swap out some parts from.

Just change out the main already!

A buddy of mine has a 2000 YZ so im going to change the cdi and see if it makes a difference. Maybe the TPS as well. Does anyone know if the 2000 will work with my 2002? Thanks guys! :thumbsup:

You can lean out your top end by raising the needle one clip, make sure you have the right spark plug as well, when you get a bike second hand you have to question everything, if you can run around fine at half throttle then the spark is proboly all good, I would wonder if it smells flooded when it stops on you or if the plug is wet when it kills... carbs can be a little tempermental, not only do I blow my jets out I remove them and look through them, then make sure they seat right yadda yadda, if you can rule out the spark then try to rule out the carb options, then you might have to think about the timing chain and valve clearance.. fun fun... :thumbsup:

I'll try raising the needles 1 clip. The bike is brand new. It was in the Yamaha warehouse when i bought it. So everything is stock. I did take out all the jets to blow air and cleaner through them and they all seem fine. I'll have to try the needle now i guess. Thanks for replying :thumbsup:

Raising the needle will make it richer not leaner! The problem, as earlier stated is probably the main (it is too large). Buy the 2-3 jets down in size (all of them). Try the next size leaner first and see what happens. You will only find out by trying. I would think that the CDI from a 2000 would work fine, the curve may be slightly changed but compatible. Again be willing to try new things, just proceed slowly. If the temperature warmed up lately it can make a differenceif you were right on the edge of your jetting. Check the gas too. :thumbsup: BTW the TPS will not make much deffernce if you just unplug it til you finish your diagnosis. I dont run one at all. One other thing to check is the vent on the gas cap, it usually will kill the bike dead if it is not working, you can just unscrew the cap a little ( only with a low gas level) I hate gas in my crotch :devil: Try em! The gas cap trick usually makes the bike lean but it is a simple check.

My friend has a 426 and it had that problem. On his the sparkplug gap was wrong. Now to fix that you need to take otu the motor and take off the gas tank and the seat and the side panels!!!!

JUST KIDDING! But that is your problem, change your spark plug with the correct one. :thumbsup:(at least I think that's what the problem is)

Hey just getting back to the notes, it is true raising the needle one clip will make it richer, I appologize I meant to raise the clip one making the actual needle drop lower, this will make it so the needle doesnt come up so far when your wide open.... You could try a 160 main jet note that sure sounds lean I run a 165 at 5000 ft with uni dual filter and fmf t4.... and I run a little rich but loose performance when I drop to the 162 main. Fun stuff eh... I am interested in hearing more details as you go... :thumbsup:

The needle has the most effect between about 1/4 and 3/4 throttle, much past 3/4 and the main jet will have the largest influence. If you're wide open when it's cutting up then try swapping the main jets first.

I have seen coils that get hot and drop voltage and run like bad when they cool down it runs good again It will make you crazy trying to finger it out

Well, finally got it all figured out and working great now! I found out it was a show room model that sat on the floor of a dealership with a bit of gas in it and the dealership went under. So it sat in a Yamaha warehouse for 2 years with this gas in it. The fuel pecot screens were quite clogged with crap and with a screen in the carb. Once it was cleaned out it worked awesome. I'd just like to put a HUGE THANKS to all who gave me ideas where to look. I learned quite a bit about the bike from everyones posts. Thanks again guys! :thumbsup:

It is fun when the solution is that cheap, though you did lose some riding time! :thumbsup:

Ya really, at least it could probably help out some other guys who may have or might have the same problem in the future :thumbsup:

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now