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Hanging idle/runaway

  • Mkdxxx
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Hanging idle/runaway was created by Mkdxxx

My little mx100 is suffering from a hanging runaway idle at times and I've gone through and swapped out everything I know that could cause a leak still does it.  'm wondering if there's something else that would cause that hanging idle that's not an air leak. 
06 Apr 2022 15:39 #1

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Replied by Bigdog302 on topic Hanging idle/runaway

might have a partially blocked pilot jet. try turning in the idle air screw and see if it gets better. if so I would clean the pilot jet. it never hurts to clean the whole carb while you have it apart to clean the pilot jet.
2 1968 DT1s,1970 RT1M,1970 DT1C,1971 RT1B,1971 Honda Z50K2,1974 DT100A 1974DT250A,1974 Honda MT250,2 1975 DT400Bs,1975 Honda CR250M1,1978 DT175E,1979 Honda CR250R.
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06 Apr 2022 17:00 #2

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Replied by msavitt on topic Hanging idle/runaway

have you replaced the magneto side crank seal?
might want to spray some wd40 around cylinder base to see if idle changes
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06 Apr 2022 18:43 #3

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Replied by Mkdxxx on topic Hanging idle/runaway

Yeah the seals have been replaced.  I've been spraying WD-40 around the carburetor and the boot in there I'll try spraying it at the base gasket to see what happens
07 Apr 2022 09:05 #4

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Replied by Mkdxxx on topic Hanging idle/runaway

One thing I noticed this last time I was tinkering with it is on occasion the gas would run out one of the overflows like the seat isn't Shutting the gas off now I don't think that's problem with being lean but I kinda wonder I find that's odd because it's I knew needle in seat I have another carburetor that I was going to put on there just to see what changes if anything The only problem is is this new carb doesn't have a Oil injector Port And I'm trying to decide if I want to figure out how to put one in Or just shut off the oil injector for the time being
07 Apr 2022 20:31 #5

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Replied by tlh0824 on topic Hanging idle/runaway

The float could be sticking open and closed-  Open it would dump fuel out the overflow if it stuck closed it would cause fuel starvation/ lean condition.
 
07 Apr 2022 20:39 #6

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Replied by RT325 on topic Hanging idle/runaway

When it settles to an idle does it idle nice & reliably or lean & faltering. Can you left the slide fully up by pulling the cable at the carb top & then let it drop to the bottom easily. Then do the same by twisting the throttle & do you get the same response--clunk on the bottom. Back the speed screw out of the way to do that. Pilot jet clear. Does the mixture screw respond to rich & lean either side of about 1.5 turns out. Now--me being stupid i know & shouldn't ask--but piston the right way around as it'll run but need choke & revving to keep it running with piston windows to the exhaust.
07 Apr 2022 20:50 #7

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Replied by Mkdxxx on topic Hanging idle/runaway

Well seems to be two issues now one is the float hanging open causing the gas to dump out and the high idle.   I have installed  a new seat and needle but something's definitely keeping it stuck open.  Poor idle period.   when it idles it idles poorly.   goes high comes down low it will die. I have found that you pull the choke out kills it right away there's just no way around keeping it running with the choke out.  Which may not say anything in itself I wouldn't expect it to run real well to choke out but I wouldn't expect it to pretty much kill it. 
07 Apr 2022 22:16 #8

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Replied by RT325 on topic Hanging idle/runaway

Is the compression right up as it should be. You'd feel it on the kickstart if it was low. Just sdaying that because it its low then you nered to screw the idle speed in to get it to sort of idle--struggling idle. But then when you take the revs up & let the throttle off it doesn't want to slow down & hangs high but might eventualy slowly slow down. So is the comp good & feel bouncy on the kick start or soft & just falls through.
08 Apr 2022 01:34 #9

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Replied by Mkdxxx on topic Hanging idle/runaway

Have not made a lot of progress.  Still has a hanging idle.  Looking at the compression now.  Want to replace the rings but for the life of me I cannot get the jug off.  Are there any hidden bolts other than the 4 head bolts.  I've been pounding the heck out of it to no avail.
01 May 2022 22:46 #10

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