Idle problems, please help!

5 replies to this topic
  • Stacey

Posted June 24, 2004 - 07:59 PM


I have a YZ450F and the bike will stay at a high idle for
5-10 seconds then when the idle drops down it will die. It runs good while giving gas, did not know if accelorator pump had anything to do with this. I have cleaned carborator out numerous times, one size up on the main jet, dropped needle one space. Bike does not snap back to idle. Please let me know if you have any ideas. Thanks

  • skthom2320

Posted June 24, 2004 - 08:37 PM


The main jet and the needle have very little to do with the jetting at idle.

You are lean on the pilot circuit. It's called a "hanging" idle. And your idle is set too low if it's dying.

Try turning the fuel screw OUT 1/2 turn or so to richen a tad. Also turn up the idle speed about a half turn. If that doesn't take care of it, put in a larger pilot jet.

  • Stacey

Posted June 27, 2004 - 05:56 PM


Thanks for the information. It seems to be working. Now I have another question for you. The bike runs great when I'm on the gas. I'm still having some idleing problems and the bike is popping alot when I let off the gas. I went up 2 sizes on the pilot and dropped the needle down 1 to number 5. Do you have any suggestions on the pilot jet and needle settings? Here is the info on my bike - 2003 YZ450F brand new motor, ported and polished head, full titanium
TI-4 Pro Circuit pipe. Thank you for your help.

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  • TimFurryBalls

Posted June 27, 2004 - 08:00 PM


I'd put your needle clip position back to stock and go back to a stock pilot. 2 sizes up on your pilot will very much richen your bottom end, and the 5th position (from the top I'm assuming) is very lean.

  • sirthumpalot

Posted June 28, 2004 - 01:28 AM


Have you double checked the valve clearances? 4 strokes can do very funny things at idle if the valves are tightening up and leaking a bit.

  • skthom2320

Posted June 28, 2004 - 08:10 PM


I'2 sizes up on your pilot will very much richen your bottom end, and the 5th position (from the top I'm assuming) is very lean.

Well, did he go from a 40 to a 42? Or from a 40 to a 45? (the pilot jets come in the following sizes -> 38, 40, 42, 45, 48)

I'd concur to start from the stock position on the needle and main.

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