2011 yz250f hard to start

[BristolA13]

I am very confused. My bike will not even begin to kick start when cold, so i have to roll start it down a hill. But after I have rode for awhile and the engine is hot it will kickstart in 2-3 kicks. I checked the valve clearance and there all in spec. I cleaned my carb out. Could it be the jetting? I'm just confused because i dont understand why it starts so easy when the engine is hot. Any advice helps!

[KRAYNIAL]

I am very confused. My bike will not even begin to kick start when cold, so i have to roll start it down a hill. But after I have rode for awhile and the engine is hot it will kickstart in 2-3 kicks. I checked the valve clearance and there all in spec. I cleaned my carb out. Could it be the jetting? I'm just confused because i dont understand why it starts so easy when the engine is hot. Any advice helps!

 

Your symptom is that of a leaking intake valve, assuming you are checking the clearances correctly.

The metals expand when hot to allow that intake to seal, and get good compression.

 

It's a common problem on valves that are worn out

Do not wait to fix this, as the next problem will be the valve breaking off.

[BristolA13]

Your symptom is that of a leaking intake valve, assuming you are checking the clearances correctly.

The metals expand when hot to allow that intake to seal, and get good compression.

 

It's a common problem on valves that are worn out

Do not wait to fix this, as the next problem will be the valve breaking off.

Thank you very much. Getting my head sent off soon to mxtime to get replaced with stainless steel valves

[Dexter42]

Wait, what's the history of the bike? Hours? Any recent work? Have you ever actually shimmed the valves? What shims did you use? Sounds to me like your lean on your pilot jet and/or fuel screw not adjusted right. Any popping/ backfire?

[KRAYNIAL]

If it idles once running, it's not the pilot jet circuit

[Dexter42]

If it idles once running, it's not the pilot jet circuit

Right on, your starting to worry me. I have an 06crf450r that I can get bump started and once on runs and idles great but won't kick start. It will backfire and pop while trying to start but can't get it to start. Cleaned the carb and then this problem happened.. At a lost.. Haven't had much time to thinker with it but only thing I check was stator to make sure it was good, it checked out ok. Going to check all connections, electrical. Hope I don't have a leaking valve... If it was the case, is their a way to test for it before removing the head?? What's the fix?? Bike has one season on valve job.

[KRAYNIAL]

Right on, your starting to worry me. I have an 06crf450r that I can get bump started and once on runs and idles great but won't kick start. It will backfire and pop while trying to start but can't get it to start. Cleaned the carb and then this problem happened.. At a lost.. Haven't had much time to thinker with it but only thing I check was stator to make sure it was good, it checked out ok. Going to check all connections, electrical. Hope I don't have a leaking valve... If it was the case, is their a way to test for it before removing the head?? What's the fix?? Bike has one season on valve job.

 

Leaking, or the gap clearance is too small.

 

You do a leak down test to verfiy valve sealing.

 

http://www.duncanracing.com/TechCenter/4-StkLeakDownTest12.2009.pdf

 

 

" cleaned the carb and then this problem happened "

 

So, you probably just removed the lower jets and reamed them.....you can't really do that to the pilot jet.

You need a new one, and you MUST clear the passage above it with fishing line!

If you have have not adjusted you fuel screw correctly, it will also be hard to start.

[BristolA13]

Also the bike does not like to idle.. Will only idle when the fuel mixture screw has the bike idling at high revs.

[KRAYNIAL]

Also the bike does not like to idle.. Will only idle when the fuel mixture screw has the bike idling at high revs.

 

Wait, what?

 

If turning the fuel screw out make the rpms go up, you then lower the with the idle screw !

 

Then try the fuel screw again.

 

The fuel screw should be the last thing you turn to get the peak idle, at the rpm desired.

 

It take a few adjustments of both to get it so the fuel screw max idle IS the idle you want.

 

 

That is how you adjust it.

[BristolA13]

My bad i meant the idle screw. It idles decent at mid rpms but once i start turning the idle screw to where it should be it just dies.

[KRAYNIAL]

My bad i meant the idle screw. It idles decent at mid rpms but once i start turning the idle screw to where it should be it just dies.

 

Right, because you are transitioning to the pilot jet

Have you adjusted you fuel screw at ALL ?

[BristolA13]

No i havent touched the fuel mixture screw.

[J_YZ2fittyX]

Kind of off topic, but do you have an extended fuel screw that you can turn easily by hand? The stock one sucks. If you dont and you want to get one, just gonna recommend the JD fuel screw...amazing feel and quality. 

 

The process of setting the fuel screw has been posted 100s of times around here (William1).

[BristolA13]

No i do not.. I will have to get one. Thank you

[Dexter42]

Well lucky for me, timing was off 1 tooth. Bike runs and starts no problem now.