Lean Revving Motor

5 replies to this topic
  • chinesespaceman

Posted October 29, 2006 - 12:14 PM


Hi Guys,

I had experienced a high revving motor on my 1999 WR400 (UK Spec). I found a slightly cracked throttle valve and replaced, I believe quite common on these.

I thought this would be it sorted, and it has been okay when taken for short runs.

However today at an Enduro, when the bike got quite warm, the motor went back to revving quite highly. Have checked all of the obvious including the cables and their routing.

Any pointers would be appreciated




Posted October 29, 2006 - 12:58 PM


Maybe your hot start is sticking or a intake leak in the rubber.Easy to check these anyway.

  • chinesespaceman

Posted October 30, 2006 - 03:11 PM


Hi Guys,

Been out and checked carburettor and can find no problems that I can relate to this problem. Jetting is as per the manual for this UK bike being used in the UK except Starter Jet is #85 (manual states #65).

The manual states Pilot SCrew 1 1/4 turns out, which is what mine is at.

The only thing I did find was that the foam air filter was sodden with water. I have never cleaned it :mad: :mad:

But would this not be likely to stall the bike.

I must state that the bike starts perfectly from either cold (with choke) or hot (without need for hot starter) and runs perfectly through the rev range.

I guess in the absence of anything obvious I will replace the filter and try it out.

P.S. The airbox cover is removed (hence water in airbox) is this safe or recommended, I see most people seem to remove this.

Exhaust and everything else is std



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  • imj75

Posted October 31, 2006 - 06:54 AM


I had a similiar problem, but without the cracked slider.
Also took the carb apart to try and find the source.
Eventually solved it by riching out the idle (test after each additional 1/2 turn out on pilot), and fiddling with the idle speed.
My '02 WR426 has a GYTR so it runs leaner on stock jetting.
Got the idle down (when hot) from about 3k rpm :mad: to a nice 800-1000, which makes it easier to ride in tough tight trails.

Pilot ended up at 3 3/4 out. Idles like a sowing machine on steroids... Posted Image

Seems the reasons it idles higher when hot is the heat leans the idling out further, and this causes the 'sticking' high idling speed.
Your description of easy starting and overall performance matches mine, so give the idling mix a try.

  • chinesespaceman

Posted October 31, 2006 - 11:00 AM


Cheers, that sounds sensible enough to me and most people recommend about 2 1/2 turns out anyway. I was hesitant to touch mine, as every other mannerism of the carburation is perfect.

Know what you mean about tight trails, since I am a newbie to enduros, which in our neck of the woods are mostly through narrow forest trails etc it's real hard work constantly feathering the clutch and using the back brake to keep the motor speed down 0 leads to early fatigue.

Anyway I will try that for sure and let you know how I get on at the weekend



  • byggd

Posted October 31, 2006 - 12:28 PM


Pilot ended up at 3 3/4 out. Idles like a sowing machine on steroids

If it needs to be that far out to run you need to replace your idle (slow) jet. :mad:


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