99 400 Idle way to high

9 replies to this topic
  • fourBanger

Posted January 19, 2005 - 10:46 PM


I need some serious help. I just rebuilt my 400 completely and it started right up. However, my idle is just way to high. The Idle Adj. doesn't even touch the throttle pulley. I rebuilt the carburetor w/no change in idle and the slide is completely closed. My next guess is the timing or electrical. My manual says how to check the timing but not how to adjust it. :cry:

Speotis Von for Bang Ur (fourbanger)
99 YZ400f
02 CR250
Trail 90 :cry:

  • spy

Posted January 20, 2005 - 01:48 AM


Have you checked the fuel screw?


Posted January 20, 2005 - 05:01 AM


Your Jetting is not correct. Balance the jetting and the idle will return to normal. This happens alot when the temps drop in winter.

Bonzai :cry:

  • sirthumpalot

Posted January 20, 2005 - 05:14 AM


.... The Idle Adj. doesn't even touch the throttle pulley. ....

Seems to me that in this case it would not run at all if everything was OK. Here are my ideas:

0) Make sure your throttle cables are adjusted properly and are not binding on anything. Does the speed change when you turn the bars left and right? If yes, then that is a sure sign that your cables are too tight or routed incorrectly.

1) Look into the carb to make sure the slide is actually closing all the way. Also make sure it's not in backwards. Search for posts on this; it looks correct when it's wrong and will not run correctly, though if I remember correctly it typically would not idle in this case.... And maybe that's only the later model carbs... I'm not sure so search for some posts. :cry:

2) Make sure your hot start is working properly. If it's stuck open or leaking then that will raise your idle.

3) Make sure you don't have an air leak between the carb and the head. An air leak can definitely raise your idle.

Hope this helps, let us know what you find!

  • fourBanger

Posted January 20, 2005 - 02:17 PM


Thanks for the help guy's. But the damn thing still idles high. I took the carb off and put everthing back to stock. I found no leaks and the hot start works properly. I started the bike with the throttle cables off and the sure enough it shot right back up to a high idle. I also unplugged the tps with very little change. Maybe, the problem's a little deeper. Thanks guy's.

Thanks Yamakaze for defending our freedom; I've served also... USMC

Speotis Von for Bang Ur (fourbanger)
99 YZ400f
02 CR250
Trail 90

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Frostbite

Posted January 20, 2005 - 05:32 PM


Check the throttle slide plate for hairline cracks at the half moon indentations, or for a missing piece.

  • Chris_from_Oz

Posted January 20, 2005 - 07:50 PM


Check your intake manifold. My 426 had the high idle problem when it was less than a year old. Turned out the manifold was split. It wasn't visible 'til I took it off the bike, so take it right off, and inspect it thoroughly. I haven't heard of anyone other than me splitting a manifold, but it's worth a look..... :cry:

  • fourBanger

Posted January 21, 2005 - 11:07 AM


I found the problem. Believe it or not that damn throttle valve plate thats on the slide was upside down. I feel like a complete moron. thanks frostbike for the images ans sirthumpalot for the idea. I sure I'll screw up something so see yawl soon.

Speotis Von for Bang Ur (fourbanger)
99 YZ400f
02 CR250
Trail 90

  • Frostbite

Posted January 21, 2005 - 01:17 PM


Glad ya found it and it was an easy although tricky to find fix.

  • sirthumpalot

Posted January 21, 2005 - 04:28 PM


Hey a free fix, that's the best kind!

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