bike will not settle down to idle


28 replies to this topic
  • pablo83

Posted May 07, 2009 - 02:20 PM

#1

I have an 01 WR426. When it's warmed up it will not settle down to ide properly. When I cut the throttle goes down to a high idle for 2-5 seconds before it settles all the way down. This is real annoying when I'm trying to compression brake down an obsticle. What causes this?

The bike has the snorkle removed, JD jet kit for altitude (9000 feet), and GYTR insert on the stock exhaust.

  • William1

Posted May 07, 2009 - 02:31 PM

#2

Drop the idle speed just a little bit, see if that 'cures' it.
Also, did you ensure your pilot jet is correct and absolutely spotless as well as the fuel screw set corretly? Even a thin film of whatever on the pilot jet can affect it. May be worth trying a fresh one.

  • davidl9999

Posted May 07, 2009 - 02:36 PM

#3

9000 ft? You riding in the himalayas??? (jk) :smirk:

Good advice above as always. :excuseme:
Hanging idle indicates a lean condition. Check that your fuelscrew is adjusted slightly rich at a high idle and between 1 and 2.5 turns out. Check that the idle speed is not set too high after making that adjustment. Check for air leaks at the hotstart connector and the engine side of the carb and boot.

  • Frostbite

Posted May 07, 2009 - 03:26 PM

#4

+1 on the air leaks, especially if it just started happening. My 99 400 was doing the same thing and I discovered a bunch of small cracks in air hoses. Most of them were on the back side of the hoses - I had to remove them to see the cracks. I replaced them and the hanging idle was cured.

  • PremixForever

Posted May 07, 2009 - 03:34 PM

#5

Lube your throttle tube/cable latley??

  • pablo83

Posted May 07, 2009 - 03:35 PM

#6

Drop the idle speed just a little bit, see if that 'cures' it.
[COLOR="Red"]Dropping idle speed does not cure it. [/COLOR]

Also, did you ensure your pilot jet is correct and absolutely spotless as well as the fuel screw set corretly?
[COLOR="red"]The carb is clean, I've been thru it twice. I don't know if the screw is set correctly, I've been dinking with it alot to try to get this sorted out. I've got an R&D FlexJet screw in it.[/COLOR]

Even a thin film of whatever on the pilot jet can affect it. May be worth trying a fresh one.



:excuseme:

  • pablo83

Posted May 07, 2009 - 03:37 PM

#7

Lube your throttle tube/cable latley??

No, why?

  • William1

Posted May 07, 2009 - 03:40 PM

#8

My esteemed collegues also make good observations regarding a small vaccum leak. These may not be readily apparent on the stand in the garage but rear thier tantrums during riding. Though, if you do have a NEW pilot jet, I suggest putting it in first and elminating that from the equation.

BTW, has it always done this or is this a recent occurrence?

Here is how to select the correct pilot and set the fuel screw:
Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method.
Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.
*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***
Turn the screw in until the idle becomes rough or the bike stalls.
if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.
If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.
Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.
If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.
If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.
If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

  • pablo83

Posted May 07, 2009 - 03:53 PM

#9

Thanks for all the advice. The mixture screw is 4 turns out. If I make it leaner the hanging idle gets worse. I'll pull the carb and put a larger idle jet in it. Another thing that's bugging me is it got terrible mileage today, so I thought maybe it was running rich, but that doesn appear to be the case.

The air leak idea sounds logical. My carb has the internal hot start so there's no hose. I'll double check the intake manifold rubber to see if something's going on there.

  • Thumper_Bloke

Posted May 07, 2009 - 04:21 PM

#10

Did that '01 WR have a TPS? If the advance is stuck, it will always idle high.
Maybe the slide is cracked? Too much air bypass will make it idle high too.

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  • William1

Posted May 07, 2009 - 04:44 PM

#11

Thanks for all the advice. The mixture screw is 4 turns out. If I make it leaner the hanging idle gets worse. I'll pull the carb and put a larger idle jet in it. Another thing that's bugging me is it got terrible mileage today, so I thought maybe it was running rich, but that doesn appear to be the case.

The air leak idea sounds logical. My carb has the internal hot start so there's no hose. I'll double check the intake manifold rubber to see if something's going on there.


Four turns is way too much. You have it right, go up in pilot jet. What size is in it now?

Make sure the Hot Start cable has a little play and the pluger moves freely in the bore.

  • pablo83

Posted May 07, 2009 - 05:19 PM

#12

Did that '01 WR have a TPS? [COLOR="Red"]Yes[/COLOR]

If the advance is stuck, it will always idle high. [COLOR="red"]what's the advance?[/COLOR]

Maybe the slide is cracked? Too much air bypass will make it idle high too.


:excuseme:

  • pablo83

Posted May 08, 2009 - 12:29 PM

#13

The idle jet was a 40. I picked up a 42 today.

  • steveracer

Posted May 12, 2009 - 11:32 AM

#14

also check the carb slide it may be starting to crack and allowing it to get extra air. happend to me and it was sucked thru the engine.:excuseme:

  • Thumper_Bloke

Posted May 12, 2009 - 04:15 PM

#15

disconnect the tps and try it.
if it doesn't change, then pull the carb off and check the slide for cracks.

  • pablo83

Posted May 12, 2009 - 06:15 PM

#16

Nothing seems to fix the problem and it keeps getting worse. Now, when the engine finally settles down to idle it just stalls, even when I have the idle stop screw at wide open. Last night I pulled the carb from my '99 YZ400F and put it in the WR and the bike did the same thing, so I no longer think it's a carb problem. What else could create this problem.

  • davidl9999

Posted May 12, 2009 - 08:40 PM

#17

Air leak, bad gas, spark problem, burnt piston, valve problem, exhaust restriction

ah, I missed that it runs but doesn't idle...
Lemme think on this some more...

  • Thumper_Bloke

Posted May 12, 2009 - 10:23 PM

#18

And it runs fine, otherwise?

  • William1

Posted May 13, 2009 - 02:46 AM

#19

Being you have removed the carb from the equation, it has to be electrical and my money is on the CDI.

  • davidl9999

Posted May 13, 2009 - 08:59 AM

#20

I'm still thinking air leak downstream of the carb. William1 makes a very good point about the CDI. :doh:




 
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