2015 YZ 250F

Tom

Tom

PR Elite
My bike won't idle when cold even with the choke out! Doesn't wanna start when cold also, but runs good as soon as it warms up and starts first kick.. HELP!! Put a brand new top end in and checked the valves, didn't help at all.. Thanks Tommy M.
 
If this bike was in My garage with what has been done to it, I would first start troubleshooting with a good leak down test.
 
Have there been any modifications to the bike?
How many hours on the engine?
How do you start it when it's cold, with the kicker or do you have to coast it?
What is the idle RPM when it's warm and idling?
Did it have the problem before you took the engine apart?
Did you take the valves out of the head and look at the faces and seats?

It may be as simple as an idle adjustment or it may be as complex as the valve seats needing cut or a stator problem? It will most likely take a qualified mechanic to rule out the basic stuff and work towards the non-basic.
 
Yes for some reson the guy over look the valves. The intake valves were very tight. I'm going to order some staneless intake valves
 
Tom said:
Yes for some reson the guy over look the valves. The intake valves were very tight. I'm going to order some staneless intake valves
Click to expand...
I just finished a 2014 YZ250F that had all new oem cylinder head , valves , springs , cylinder , mains , I rebuilt the crank ! It did not start cold after just a month and half, their problem was dirt getting past the filter ! Ruined the new valves fast !!!!! I would take a close look at the intake boot after the filter, You should be able to see if has been eating dirt ! IMO there is nothing wrong with YAMAHA oem valves, never switched one to stainless valves !
 
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