yz250 Idling High

keeptwostrokesalive wrote: So my 2006 yz250 has been idling very high, and no matter what I do it will not stop. When I looked through the manual its said do not remove the TPS because it might cause a drop in performance. Unfortunately though My Dad removed the TPS before we saw this in the manual and Im wondering if this may have something to do with the high idle. Have any of you had this happen with your yz250?

I would first look at the throttle cable and the way it is routed, if that looks good I would check for a "Air Leak"at the main seal behind the stator/flywheel. What does the color of the plug look like? That can give you an idea what to check next.

Well I adjusted the carb slide and it went back to its normal idling level. Now the bike is just running really rich. I tried moving the jet needle down in order to get less fuel but its still running rich. What can I do to fix this? I am an idiot when it comes to jetting a bike.

OK now you have to ask what has changed since you have the problem? It can something simple as a dirty air filter or even a shop rag in the air box. Have you changed pre-mix oil? If your running pump gas did you change dealers? or have they changed fuel because of weather? Take a look at your manual on reccomended jetting. One other thing have you cleaned the power valve lately?

xnationalwrench wrote: OK now you have to ask what has changed since you have the problem? It can something simple as a dirty air filter or even a shop rag in the air box. Have you changed pre-mix oil? If your running pump gas did you change dealers? or have they changed fuel because of weather? Take a look at your manual on reccomended jetting. One other thing have you cleaned the power valve lately?

Well I just recently bought the bike from a redneck off of craigslist. I believe he was running 93 octane gas with yamalube oil and it was still running rich. I am currently running 93 octane gas with 2 ounces of maxim octane booster per gallon. The bike has an FMF gnarly pipe that I put on there cause the FMF pipe that was on there was smashed. It also has an FMF power core II silencer but I am going to order a pro circuit r304 silencer tonight because the current one on there now is beat to hell. I also just installed Boyesen pro series reeds. I moved the C clip up one notch on the jet needle which put it on the last groove and the bike is still running rich. The bike has spooge coming out of the case where the connecting rod goes to the power valve so I will most likely remove the cylinder today and clean that area and the power valves out. And then I will replace the faulty seal. I believe the bike has stock jetting also. Hopefully this is enough info for you to help me figure out my problem.

Thanks for the help.

And one more thing. When I tried to start the bike the other day it shot out air out of the exhaust a few times before it cranked. I dont know if that is good or bad.

Hopefully you got the manual with it so you can study it. Again I would check the air filter for cleaness and to make sure its not overlubed with air filter oil, I would also check the power valve to make sure it isn't sticking or hung open (especially since you don't know how the bike was serviced). Take notes on what jets are in the bike and then see what is stock and adjust accordingly (also check with FMF or PC with what they recommend for jetting with their exhausts) Also what ratio gas/oil are you using? That can be something to look at also. Inspect the reeds to make sure they are sealing also.

I am running 32:1 with klotz supertechniplate. I do have a manual and the filter was clean and not over oiled. I am getting ready to remove the cylinder to get to the power valves and I am expecting there to be a lot of spooge in that area. The Reeds are brand new and are sealead correctly. I have ridden the bike 3 times so far and the one thing I noticed when it finally idled correctly is that its lacking on the bottom end and Im having to use the clutch more than I would like. Now its time to go start the dissasembly.

So upon dissasembly this is what I discovered. Here is the cylinder head with multiple dings in it. Im assuming this is the start of detonation and probably resulted from the previous owner running low octane.




And here is the power valve area which to me is very confusing.

You might inspect the rod bearings (both big &small) and make sure there is no play or damage to the bearing cages. The power valve looks like it needs to be cleaned and make sure it opens and closes smoothly.

The powervalves open and closes perfectly with no problems. What is the rod bearings? Thankfully the crank had no up and down movement but it did have a little side to side movement which is fine. Also the piston and cylinder were still in excellent shape.

Rod bearings are the needle bearings that the connecting rod rides on, and if the rod has no up & down play they are usally ok. The power valve looks gummed to me and you might need to use some connect cleaner on it.

Dings on the head look old....and from something hard...who knows.....detenation will look more sand blasted and in a more uniform pattern and would probably see it on the edge of the piston too. being as your already there, replace the oil seal in the cylinder the the PV rod slides through, at first the PV assy does look complicated, but when you dis-assemble once, it all makes sense and is very easy, just pay attention when taking apart. your MJ should be 178 stock, probably go up to 180 with a pipe, assuming you stay on pump gas.

go over to thumpertalk, the Yam 2 stroke section, more info...

kijen wrote: Dings on the head look old....and from something hard...who knows.....detenation will look more sand blasted and in a more uniform pattern and would probably see it on the edge of the piston too. being as your already there, replace the oil seal in the cylinder the the PV rod slides through, at first the PV assy does look complicated, but when you dis-assemble once, it all makes sense and is very easy, just pay attention when taking apart. your MJ should be 178 stock, probably go up to 180 with a pipe, assuming you stay on pump gas.

go over to thumpertalk, the Yam 2 stroke section, more info...

I am going to replace the seal as soon as I get the powervalve area all dissasembled. Unfortunately I stripped one of the allen head screws and I am going to have to drill it our. Maybe its just me but I always seem to strip bolts.