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vacuum question

  • Thread starter Thread starter scottychop
  • Start date Start date
S

scottychop

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Started diagnosing high/runaway idle this afternoon. At first I thought it was a fuel delivery issue, but got the petcock to perform as normal. Then tried to start things up and it cranked for like 30 seconds with nothing doing. Tried this four or five times. sixth time, it starts to bobble. Seventh time, it fires and I get the high idle. What's building, the pressure? Vacuum in the fuel delivery? Why does it take so long to start up? Yes, this happens every time I start the bike.

1. Replaced the intake boots, o-rings, and cleaned the carbs.
2. Did a valve adjustment. It's possible the exhaust side are still slightly out of tolerance on the loose side.

3. And here's the vacuum part: Got it running at normal idle. Give it some gas and the revs go up, and SLOWLY come back down. I notice the vacuum port for the petcock is open. Oops. Cover it with my finger, give it some gas and it revs up....and stays up. Let my finger off the vacuum port and it slowly comes back down. What's going on here?

Carb guru I need you!
 
Isn't this the classic hanging idle problem? You said you changed them but when were your intake boots and orings last changed? Is the airbox properly sealed? Where are your mixture screws? Could the diaphragms have slipped out of their slots in the carbs (I was just told about that tonight)?
 
Yup, the classic hanging idle issue alongside a terribly difficult start. I think there has to be something going on with vacuum for the hard start/ fuel delivery issue. Not sure on the idle problem. Everything has been replaced and or adjusted to spec.
 
scottychop said:
Yup, the classic hanging idle issue alongside a terribly difficult start. I think there has to be something going on with vacuum for the hard start/ fuel delivery issue. Not sure on the idle problem. Everything has been replaced and or adjusted to spec.
Click to expand...
Sounds like "choke" circuit isn't behaving- maybe your throttle plates are not closed enough to let the "choke" system work. But this would cause a high idle as soon as it caught.
 
Hi,

Is the vacuum line from the carb connected to the vacuum port on the petcock? Is the airbox installed?

Thank you for your indulgence,

BassCliff
 
It wasn't. Thus the finger move. I would have guessed that the opposite would be true and the idle would hover with the cap open, not closed.
 
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