easy idle question (for some one!)


7 replies to this topic
  • mac the knife

Posted May 30, 2013 - 11:46 AM

#1

ha all,
i have now got my wr400f running great, the only problem is hanging idle!!! all the jetting and fuel screw settings are standard. is there any possibility that it could be electrical?
when the idle hangs high, i can blip the kill switch and it will bring the revs back down to normal ? hence the question about electrical !!
any help would be greatly received
mac

  • Krannie McKranface

Posted May 30, 2013 - 12:28 PM

#2

Hanging idle is a function of a lean pilot circuit.
It can be caused by several things.

The most COMMON thing is mis-adjusting your fuel screw.

Start with the fuel screw at 1 turn out.

Start the motor, and drop the idle with the idle screw as low as it will go.

Now adjust the fuel screw for max idle.

If it goes to high, drop it with the idle screw, and repeat.

  • grayracer513

Posted May 31, 2013 - 06:46 AM

#3

Possibilities are:

Any sort of air leak in the intake (including via the hot start system)

Tight intake valves

Internal leak within the carb body (very difficult to isolate except by ruling out everything else

Incorrect pilot screw adjustment or partially clogged pilot

Ignition timing problems (extremely rare)

  • Do I Care?

Posted May 31, 2013 - 11:33 PM

#4

I had this problem and it turned out the 0-ring on the fuel screw was missing from the PO taking it apart.

Also, these carbs can be hard to set the idle speed...

Turn your fuel screw to 2 ~ 2 1/3 turns out (whatever is best).
Then adjust the idle speed from the black knob. This should be slightly high. There is not much between idling high or too low. Find the setting that works in conjuction with the fuel screw setting.

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  • Do I Care?

Posted May 31, 2013 - 11:35 PM

#5

ps. this is not to take anything away from the above info and all mentioned should be checked also.

  • mac the knife

Posted June 01, 2013 - 06:49 AM

#6

cheers guys, thanks for all the advice. the wr is having its MOT ( road worthy inspection) next week so i can ride to the green lanes instead of putting it in the van. lets hope i can sort this hanging idle before then. first job will be looking for any air leaks.
thanks again
mac

  • grayracer513

Posted June 03, 2013 - 08:06 AM

#7

I forgot to mention the possibility of the fuel screw being gone altogether.

  • Do I Care?

Posted June 03, 2013 - 08:29 AM

#8

Or the O-ring perished, carb slide plate the wrong way up, float needle valve O-ring perished (but it would leak from the overflow is it was the float needle valve O-ring perished ).




 
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