Jump to content
Sign in to follow this  

YZ250f cold starting problems

Recommended Posts

I just bought a 03 250f, and it has a hell of a time starting cold. when it is warmed up it has no problem at all. My father says " its wore slam out" , but im thinking the valve clearance is too tight, and when it is cold the valves are not fully seated. Would any of you experts back up this theory of mine. Do the valve clearance usually get looser or tighter? any of your input would be great. I know this might be FAQ, but I have not found anything about valve clearance getting tighter. The guy I bought it from said that the valves were replaced and has not had a adjustment since then. Is there a guideline on how many times you can adjust the valve clearance before it is trash.

Share this post


Link to post
Share on other sites

I have the same bike and here is how I start it cold. Pull choke, kick 2-3 times, one full twist of throttle, kick 2-3 times, one full twist of throttle, kick 2-3 times. Usually starts 1-2 kicks after the second throttle twist. Before I started doing it this way it took 15 or so kicks to start the bike.

Share this post


Link to post
Share on other sites

what about the valves? when they go out of clearance, do they get on the tight side and keep the valve from seating? or do they get loose and have excessive clearance. Im sure there is some Yamamaster who has seen a few of these.

Share this post


Link to post
Share on other sites
what about the valves? when they go out of clearance, do they get on the tight side and keep the valve from seating? or do they get loose and have excessive clearance. Im sure there is some Yamamaster who has seen a few of these.

Yes, for a well adjusted set of valves, after a while when the valve train wears down, the valve clearances tend to get tighter. When there isn't any clearance left, your valves will have leakage problems making it harder to start and the engine will have less power overall when running. I don't believe this condition will cause any engine failures, just harder starts and lower overall power.

On the other hand, if you have brand new valves and your clearances are too tight, this will expose the valve(s) to be too close to the piston making it more prone to engine failure due to such things as valve float at high rpm causing the piston to hit the valve, breaking the valve and locking up the engine. So on a new set of valves, IMO, it is better/safer to be on the loose side of the spectrum for valve clearances even though you might get slightly less HP out of this setting.

Check your valve clearances to be sure of where your settings are, especially when the valves are new to get a baseline set or measurements (this is very important since the new valves are the longest valves). See the following link to show you how to check the clearances, it's not hard:

http://www.thumpertalk.com/forum/showthread.php?t=394312

Share this post


Link to post
Share on other sites

There is definitely somthing going on in there. I'd either check the valve clearences yourself or take it in and have the valves looked at. I just bought an 02 and it starts first kick when cold.

Share this post


Link to post
Share on other sites

just checked them last night. Exhaust valves are in spec, but the intake valves are way tight. I cannot even get a feeler guage between the cam and the lifter bucket. Im going to stick a dial indicator on the bucket and unbolt the cams and see how much the valve will raise. I guess this will let me know if I have to remove the head and send it off. Thanks for the advise

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

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

Reply with:

Sign in to follow this  

×