Jump to content

Carb help please

Recommended Posts

Ok guys, I have a problem that I need to get figured out on my 09 yz450. It runs perfect, starts perfect 95% of the time. Trouble is halfway thru a harescramble it wants to die if I'm choppy on the throttle mainly in tight stuff and if it dies under load it will not restart for 4-5 minutes. But if i shut it off with the kill switch when it's hot it starts right back up.  I have added things to help cure this problem. The bike has a rekluse Exp 3.0 which is adjusted correctly, flywheel weight, and I just recently adjusted and wired the accelerator pump arm/cam(which completely eliminated the off idle bog) honestly thought that was going to fix it but it didn't. I've reached the end of my ability to reason with the thing. What else can I check/do to remedy this problem?? Any help would be greatly appreciated 

Edited by Wr822

Share this post


Link to post
Share on other sites

If the jetting you have works before it gets hot, it's not the jetting.

It sounds like what you are experiencing is 'flame out', which leave unburnt fuel in the cylinder, making it hard to start.

Try this next time: when it stalls, clear the cylinder before trying to start it: WOT, kill button held down, kick through several times.

Then start it with no throttle, but maybe some hot start.

I would also make sure your fuel screw is adjusted properly: hot motor, set the fuel screw to one turn out, and then lower the idle as low as it will go with the idle screw. Raise the idle back up with the FUEL screw, till the rpms stop rising. It's subtle.

Share this post


Link to post
Share on other sites

See that's what's weird(to me anyway) the jetting is fine when it's hot too it's just when it flames out. So you're saying you think the fuel screw needs adjustment? From what I understood from grayracer when he helped me set it when I got the bike a few years ago one thing that stuck with me was that carb tuning was a big "give and take" game, if it's REALLY good at something, it's not gonna be good at something else. And where it is set works perfectly, it didn't wanna start well before I set it and now it's great so I'm scared to mess with the screw... about ready to give up and either go to a FI with the magic button or stop racing in the woods, neither of which I want to do😔

Share this post


Link to post
Share on other sites

You should be adjusting the screw everytime the air density changes. For me, that is every single ride, as it changes from morning to afternoon.

Get an R&D fuel screw to make it easier.   You only adjust it with a hot motor, never cold. 

Also, you should be changing the fuel screw oring every year, as they start to leak. Same with the slide plate seal and the emulsion tube, but maybe every two years/ 100+ hours on those.

Share this post


Link to post
Share on other sites

Yea I'm sure the slide plate seal, fuel screw O ring or emulsion tube has never been changed and it's 8-9 yrs old with 65hrs. So is a "flame out" a rich or lean condition?

Edited by Wr822

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:


×