Help.....Bike won't start

my buddy crashed my bike a few weeks and bent the header pipe so i bought a used pc system off ebay and put it on. The tempurature dropped a lot and it is about 15-35 degrees out now and when it was last running correctly it was 55-75 degrees. The fuel screw was turned out 2.5 and it wouldn't even fire. I turned it to 1.5 and now it backfires every few kicks and every once in a while it starts running for a second then shuts off and starts backfiring again. Could i have to rejet it? It has the stock jetting right now. Any help would be appreciated. This is really frustrating. By the way this is a 2002 yz426.

Sounds like you're in the ballpark with the fuel screw being 1.5 turns out.

I don't think the pipe would make that big a diff.

Maybe something jarred loose in the crash. Check all the stuff like the throttle position sensor, wires, etc.

Put a larger starter jet in it. Not the pilot or main. The starter jet. Its in the bottom next to the pilot and main. The starter only works when the choke is on. When its cold out this circuit runs lean causing the bike to start and stall repeatedly untill builds enough heat to stay running (or fowl a plug). I go from a 65 to a 68 in temps from say 55 to 30 deg. Below 30 deg I use a 72 starter. YOu may also need to go to a bigger pilot and main due to the temps. But the starter jet will at least get it running. you can figure out the rest of the jetting from there.

BTW - If it's colder out, you need to richen things up. You leaned it out when you turned the fuel screw in.

Be sure you're using the choke, and before you go crazy put in a new spark plug. The temp change can certainly cause your symptoms, but your symptoms also match perfectly with a fouled plug.

Yep, I agree with the post above me completely.

You fouled the plug.

Either put in a new one or take yours out and brush the hell out of it and put it back in. I kicked mine until I was blue in the face a few times because it kept firing like that. A new plug and it purrs first kick.

yeah that could be it because i cleaned it really good and put it in and it started a few days ago and then i tried it today and it wouldn't start.

It's cold out give the throttle about 5 full slow twists then kicker over :applause:

yeah that could be it because i cleaned it really good and put it in and it started a few days ago and then i tried it today and it wouldn't start.

That's definitely it! If you start the bike (or at least if you start my bike) and don't let it get up to full temp, then shut it off; then the next day it needs a new plug.

The plug gets caked with gas or gas+oil, and instead of the electricity jumping a spark, it just travles over the liquid part and no spark. To clean the plug, put on some goggles and hose it good with carb cleaner, especially down around the electrode. Blow it off, put it in and you're off! Next time you fire it up to show your buddy, let it get nice and hot before you turn it off!

Sounds exactly like the problem I had... only I melted the piston.

Sounds exactly like the problem I had... only I melted the piston.

well it runs fine once its started. I'm gonna pick up a new plug tomorrow. Thanks for the help everyone

I wasnt implying that was your problem, I was just throwing that out there.

Put a larger starter jet in it. Not the pilot or main. The starter jet. Its in the bottom next to the pilot and main. The starter only works when the choke is on. When its cold out this circuit runs lean causing the bike to start and stall repeatedly untill builds enough heat to stay running (or fowl a plug). I go from a 65 to a 68 in temps from say 55 to 30 deg. Below 30 deg I use a 72 starter. YOu may also need to go to a bigger pilot and main due to the temps. But the starter jet will at least get it running. you can figure out the rest of the jetting from there.

YZman, no wonder I've been having issues starting my bike and it keeps dying; I should go with a larger starter jet! What if it's above 55 . . . would you still go with a 68? (I assume stock is 65.)

Needs new plug. I had a 2001 426 and every once in a while it wouldn,t start, put new plug in and first kick fired right up

YZman, no wonder I've been having issues starting my bike and it keeps dying; I should go with a larger starter jet! What if it's above 55 . . . would you still go with a 68? (I assume stock is 65.)

The correct starter jet for the tempatures is definately a start in the right direction. if its cold enough the rest of the jetting may need work as well. But that starting and stalling like 10x before it stays running is all the starter jet. Some say turn the fuel screw out. Others say twist the throttle more. What they are doing is trying to get more gas into the motor to cover for what the choke circuit should be doing. I run the stock jet in the summer when its warm out. I dont swap them out till it starts getting colder out.

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