Hanging idle


11 replies to this topic
  • gio

Posted February 09, 2008 - 07:30 PM

#1

Hey guys i have read several threads on this issue and they are a bit conflicting in advice.
.
My YZ400 has a high hanging idle once warm. It has a 42 pilot (1 size smaller)
standard needle jet (3rd groove, 1 position leaner than stock), 168 main and the rest is stock.
.
I did the pilot ciruit test and found out my pilot jet was 2 big therefore i went one size smaller to the 42. Doing the pilot circuit test again it appears it may be just one size too big. But once warm when i blip the throttle the idle hangs for about 10 seconds sometimes longer and then returns to normal (which is really low)
.
When i try to set the idle to the correct speed the idle hangs even higher once i blip it. Is this a lean condition or a rich condition or is it something else (not carbie). The fuel screw is set a 1 turn, but can almost run with it closed, which i know means it is too big.
.
Need help to diagnose the problem. I have already pulled the carb and the jets were clean, set the float height and all appears to be working fine.

  • ThumperKid250F

Posted February 09, 2008 - 08:19 PM

#2

on my 06 yz 450 when it it fully warmed up if i blip the trottle it hangs for about 2 or 3 seconds the most then returns back to reg idle.. i dont no what it is but the bike is running strong so im not really concerned with it..

  • hyperlite33

Posted February 09, 2008 - 09:09 PM

#3

My '01 426 does this when the engine is fairly cool but not more than a 3-4seconds. I know this may not be what you want to hear, but I would just run your bike...might even be bad gas! :applause: When my gas was a little old when I bought it it hung up for a lot longer than it does now.

  • William1

Posted February 10, 2008 - 02:53 AM

#4

Hanging idle is a sign of a too lean pilot circuit.

  • ben_suhard

Posted February 10, 2008 - 06:30 AM

#5

Yep, a sign of being lean, it could be that extra air is getting in somewhere on the engine side of the carby. Is the little rubber o-ring still on the end of the fuel screw?

  • gio

Posted February 10, 2008 - 11:51 AM

#6

Yep the o-ring is still on the fuel/pilot screw. When i do the pilot circuit test the bike still runs with the fuel screw closed. So i assumed the pilot jet was too big.
.
I'll guess i will have to check for air getting in somewhere.

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  • todds924

Posted February 10, 2008 - 04:35 PM

#7

Yep the o-ring is still on the fuel/pilot screw. When i do the pilot circuit test the bike still runs with the fuel screw closed. So i assumed the pilot jet was too big.
.
I'll guess i will have to check for air getting in somewhere.


What pilot jet did you have before you changed to the smaller? It sounds definitely lean.

  • Kylelind

Posted February 10, 2008 - 05:55 PM

#8

I was having this problem on my 00 426 and I opened the fuel screw up a little and it is gone. richen it up a little.

  • gio

Posted February 10, 2008 - 10:50 PM

#9

I think it was standard 45 but the number was very hard to read on the jet.
It also started with no choke (cold) with the standard PJ and the fuel screw could be turned in all the way in and it kept running.

  • todds924

Posted February 11, 2008 - 05:56 PM

#10

I think it was standard 45 but the number was very hard to read on the jet.
It also started with no choke (cold) with the standard PJ and the fuel screw could be turned in all the way in and it kept running.


1 turn doesn't seem enough on your fuel screw. Try 2 turns and see what happens.

  • BBrown626

Posted February 12, 2008 - 12:57 PM

#11

Couldn't this also be the TPS? I believe that if it is out of adjustment you will get the hanging idle too.

  • todds924

Posted February 12, 2008 - 07:54 PM

#12

Couldn't this also be the TPS? I believe that if it is out of adjustment you will get the hanging idle too.


No. you can just disconnect the tps and the bike will run fine. I know some people who disconnect the tps because they had surging problems at steady throttle. This fixed it. If i were you i would try 2 turns on the screw with what you have in there. If it doesnt help, put the bigger pilot back in it...then set your mixture screw again.





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