I have a '04yfz450 and the friggin thing cuts out and sputters when I get on it in high rpm ranges. It's not the rev limiter, it shouldn't be kicking in at these rpm levels.

Someone said something about it may be floating valves. Can someone give me cause's and symptoms of floating valves?

 

Floating valves are when the valves are bouncing on their seats at high rpm's this is caused by weak valve springs. I would check your main jet in the carb for a clog. If your quad is not stock as in jetted it may need a richer or leaner jet also check the spark plug cap for a loose connection that is not showing up till high rpm's and vibration

 

I'm pretty sure that it's not floating the valves. Your rev limiter will hit before that happens. It may be too rich. As the weather gets hotter things run richer due to less dense atmosphere. You might need to lean it down for the summer.

 

thanks for the reply. I'm dying for help here. It's definatly not running rich. I checked it out and the guy I bought it from was running a 146 dynojet. I'm not sure what that is equivalent to but I'm sure it was too small. I stuck a 165 main in but its still cutting out. Almost like it starts missing.

Anyone that can plz help me with this prob. I don't want to take it anywhere to get it worked on but I don't know where to start myself.

 

Did you have the same symptoms with the 146? Did you replace it with a 165 Dynojet, or other brand?

 

It did have the same symptoms with the dj146 and the 165. I just went with the keihin jet on the 165.

 

This is not going to sound good, but you did not mention that you had a new cam ! take the covers off and check the valve springs to see you havent cracked them. It can happen if the this problem has just happened , especially if like me you gun it everywhere poss. Valve float is not going to be the problem if the springs are ok. If its electrical you will get the ignition of the fuel in the exaust when the engine revs drop, if its the carb then this wont happen it will just cut out or miss fire.

 

Ok, thanks UKPaisley. I have somewhere to start. The guy told me it was had a HotCam but I won't believe it till I see it. I'll start with a good carb cleaning then check the springs. If I have to tear this thing down and it don't have a cam, it will when I'm done!

 

If you were running a jet kit in it, running the keihin 165 will only worsen the problem. You are then running a jet with a needle that were not meant to be used together. Run dynojet jets with dynojet needles and stock style jets with the stock needle. For a piped and filtered YFZ, a dynojet 146 should be on the money. However with a cam you will need to go higher. The dynojet jetkit usually goes to around a 165 for the YFZ if you purchased the stage 2. Jet it up with those. They are a better setup than the factory style.

Make sure the fuel system is clean first though.

 

Man, I hate those dang jet kits. So a 146dj is like a 165 keihin for a yfz but a 170dj is like a 155 keihin for my 400ex.

Thanks for the Info SpDdEmOn.