2009 YZ450F - Fuel issue (Carb)

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5/22/2018 6:21 PM

Ok so this forum never fails and i have great success with people helping me with my bike. so this is my last resort before i rip the bike apart and look for the problem.

So, i have taken my bike to 3 dirt bike/racing shops and they all wash their hands of the problem. They say they have a pro rider and he said there is nothing wrong with the bike.

Here's the problem: First of all when the bike is cold, it is hard to start, takes maybe 8 kicks or so with the choke out. when I get the bike running with the choke out it runs ok but as soon as the choke is pushed in it idles real low and eventually quits. when i get the bike in gear and ride it, it coughs, spits and stutters as well as the exhaust pops like crazy. I'm not sure if it needs a carb clean or some jets replaced but i was hoping i could get some input here. I was told by a mechanic that the needle and seat but I'm not sure if that is right.

Any input is greatly appreciated. Thanks.


5/22/2018 8:43 PM

Try 52 pilot jet. 2.5 turns out on the mixture screw.


5/22/2018 9:02 PM

Also tear apart the carb again. Check everything including the slide and seals for the slide


5/22/2018 9:05 PM

If it ran fine recently, look at the rubber seal in the slide. Almost guarantee it has a bad spot in it. If it doesn't seal perfectly it will run like Ass.


5/22/2018 9:31 PM

Start with a new pilot jet one size larger from stock. New. Not just cleaned.


5/23/2018 4:23 AM

Thanks everyone for the replies.

So I take it that I need to take the carb out and out new pilot jet and needle in it? As well as check the slide. Is the reason why it is spitting is because of the Jets clogged or the seal? Or both?

Thanks again


5/23/2018 5:09 AM
Edited Date/Time: 5/23/2018 5:10 AM

Does the YZ450 have the same hot start setup as the 250f of that year? If so, it’s very common for the plastic hot start plunger to rip the threads out of it and pull out of the carb, causing the exact issues you’re having. My 09 YZ250F did that almost new, I installed a Pro Circuit billet plunger and that fixed the issue.


5/23/2018 5:44 AM

Check the fuel screw setting and make sure the o ring is good.

Paw Paw


5/23/2018 6:39 AM

Yes it has the hot start set up. I never use it tho. I will check the fuel screw and other things before I take the carb off


5/23/2018 6:45 AM

Had an 08 yz450f. One of my favorite bikes. Should never sold it.