09 yz450 hard starting after shut off/stalled-help please!

Hey guys, just picked up a 09 yz450 and it runs great, around 14hrs on it, only problem I am having is that when I shut it off or stall it, it WILL not start for about a minute or so. If I let it sit for a minute after shutoff, it fires right up first kick most of the time. What could cause this? I also heard about a cause of problems in these carbs is that rubber gasket on the slide needs replaced every season or so and pretty much nobody does it, any truth to that?

No truth.  Not unless you are running some unusually nasty fuel.  If you remove that seal, it will always look rumpled and half dissolved, but if you let it dry overnight, it will normally return to its original shape.


Assuming that the bike runs OK while hot, your starting problem is typical of a poorly tuned idle circuit.  Quite often, people will fatten (make richer) the pilot, or idle, circuit in order to improve throttle response, or help cure a bog, whether it's real or just something the rider is causing, instead of tuning the stumble out the correct way.  Trim out the idle circuit according to these two posts and see how it runs after that.





That's what is so confusing to me is that the crispness of the throttle is so good and it runs so perfect I am leery of even messing with it. I have not had it apart though so I don't know what it's jetting is, I guess I can do that, and compare to your optimal settings. I just thought I would ask before I did that in case it was a known symptom for someone like yourself. Thanks gray

OK, well, there you are.  You have an '09 with what you describe as "crisp" throttle response.  Most of them didn't start out quite that way, and there are different ways to get there from where they started.  Some are clearly better than others, especially because some ways of getting that snap will make your bike run worse.   It'll have plenty of throttle response, but it will either blubber through part throttle corners at low or mid speed, Or idle fast, or flame out when the throttle is chopped shut from a third open or better at lower speeds.  Or it will be a bitch to hot start.  Or any number of those together.   Doing it right is more work, but really doesn't cost much.


If you do the idle adjustment and find out that it was too rich originally, ride it and see if it changes the throttle response, and whether it starts better.  If the second link indicates that it needs a smaller pilot jet, then try that, too.  If you get it to start the way it should, but you loose enough on the crisp response side that it bothers you, you can fix that another way.

Awesome, thanks a lot, I'll check back in once I check it out the way the second link explains, thanks again!

Yea I don't understand what it's supposed to mean that it drops or misses? And smooths out? These don't have a single spot where the idle sounds like it is smooth, it's either revving out or turned down so low it's dying, what am I not getting?

These don't have a single spot where the idle sounds like it is smooth, it's either revving out or turned down so low it's dying, what am I not getting?


They do when the pilot is clear and the correct size.  You are turning the pilot fuel mixture screw on the bottom of the carb, and not the idle speed thumbscrew, correct?  Sounds like the pilot is too big.  Do you know what size it is?


What is supposed to happen is that as you turn the screw in, you should reach a point at which the idle begins to drop, or turn rough.  As you back out from there, stop when you just get to the point where the idle smooths out.  That should be close to 1 3/4 turns out from seated.

Ok, is turning "in" clockwise like a normal screw? What pilot jet SHOULD I have? I don't know what's in it.

Edited by Wr822

Ok I got it readjusted this morning to 1 3/4-2 turns out and it is starting 1st kick almost every time even without the hot start but, I only rode it around the yard for 5-10 min, I'm not sure what it was turned to yesterday but I didn't think it was too far off from that when I was riding trails but it wouldn't start for 10+ kicks most of the time then, would the type of riding you're doing at the time make a difference? I wouldn't think it would but it seems to matter with this bike...

Edited by Wr822

How far off would "not too far" be?  A half turn is a pretty big deal, most times.


And yes, "in" is clockwise/tighter.

No clue how far off I was because I've never really messed with jetting before and didn't have the proper screwdriver and it kept slipping out of the slot and I finnaly said screw it because I wanted to ride, lol. But I had some patience this morning and took a little more time and it seems to be starting correctly, thanks for the help. You use a 45 pilot on yours? But its not necessarily the right one for all yz450s from what Ive read?

Depends where you are.  Most '09's are usually happier with a slightly smaller pilot than the '06 is.  42-45 is a realistic range.

Create an account or sign in to comment

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

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now