2000 yz125 flood and bogs after bike gets warm

I'll try and give as much information as I can in the original post, but I need help.

My friend has a 2000 Yamaha YZ-125

Bike has always run great. 2 years ago he put in a new Top End (all OEM)and ever since he has been having the same issue. The bike starts, and runs great from cold for roughly 10-15 minutes. Once the bike heats up, it will bog down at higher RPM's until it eventually shuts off.

We've pulled the plug and its dripping wet with fuel. Other than the top end being rebuilt, everything in the bike has remained the same. Same fuel ratio, same carb and jetting, same air screw setting. Everything has been set back to factory specs. We thought maybe the ignition coil was bad, swapped it with a known working coil and it did the same thing. We've disengaged the kill switch thinking maybe the kill switch was shorting out, still same issue. We've pulled the carb, check floats, needle valve, jets and everything. Everything is still great and in working order. The reeds seem to be ok and in working order also. I'm at a complete loss. I've sprayed contact cleaner around the cylinder head while the bike was running to see if I had any type of air leak and still nothing. It's a major issue. Please anyone with any advice shoot it my way.


Hi there

and how is his jetting, mostlikely way to rich at the main. The info needed is the the jetting, the highs of the riding area and what kind of temps.

Good luck


I really hope you're not over looking something simple like a dirty (or over oiled) air filter? Try running BR8EG plug, the warmer spark may help resist fouling.. Perhaps the right side crank seal is leaking tranny juice into the crank case??

Likely culprit would be rich main jet or needle setting.. Good luck

Main jet is a 380, bike calls for a 360. But again, the bike has always run fine on that 380 jet ever since he's owned the bike. We've been running all of our tests without the air filter because we know his is currently dirty and could potentially be the problem. I've been racking my brains over this. I'm actually losing sleep over this.

Btw we have been running BR8EG plugs as well. We know it calls for a BR9EG but I figured the 8 may be more of a help at the moment than the 9. Most of the riding done is normal trail to track riding. Temps between 50-80 because we leave in the North East part of the States, the weather can fluctuate so much during riding season.


not very recommended to run a bike, any bike without air filter. Cleaning it shouldn't be a problem. Have you pulled the cylinder off, as the problem started after putting a fresh top end in who knows what went wrong.

Edited by arnego2

Check the stator.

You will NOT get any verifiable results running a bike without an air filter.. :thumbsup: Clean the filter, put in the stock jetting and then ride it..

Maybe your power valve is not engaged/timed properly.. Did you put the piston in backwards?

May be time for another top end... its a 125 and the top ends been in there for 2 years. The most time a top end ever saw in my 125 was 20 hrs when I was lazy. Checked compression?

I've yet to check the stator or the power valve. Those are my next two things to look at. Even though the top end is 2 years old, it only has about 45 minutes on it because of the issue that it's been having. We can't keep the bike running for more than 5-10 minutes at a time. I did not replace the top end myself, but my friend who did the work insists that he put the piston in correctly.

That being the case, your next check should be that the power valve mechanism is timed correctly.. :thumbsup:

Also, when checking the PV, might as well shine a light in the cylinder (the exhaust needs to come off) and make double damn sure the piston is NOT backwards.. :thumbsup:

im having the same problem with my 2000 yz 125.the top end was fresh when i bought it. every one i have talked to says power valves.if so what do i check for and how do i fix it?could they just need cleaning? also it seems like the powerband dosnt kick in at lower rpm like it should

Have you checked gas tank cap vent line to make sure its not stopped up?

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