Leaking vacuum advance symptoms?

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Driven

Well-known member
Joined
Oct 27, 2012
Messages
50
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Location
Maine
Hey guys, been chasing a lean hesitation at steady throttle, especially noticeable at 3000rpm. Carb sync is perfect, idle circuit clean and adjusted, valves in spec, etc. Decided to check my vac advance with my Mityvac and it doesn't hold any vacuum. I can hear it moving but the gauge drops to zero. Could this have been my issue all along? I understand there is no fix for this other than plugging the line at the carb, correct? Will I have to resync once I plug the line?

Thanks in advance...heh heh.
 
Would this be causing a lean condition and will I have to re-sync?
 
Won't have to resynch. It will cause lean condition and the hesitation. I replaced my vacuum advance so I know it can be done. I do not know of any source for a new vac advance. I installed a used one.
 
I'm just excited to get rid of the hesitation! Been driving me nuts trying to find the cause. I'll tackle the advance this winter. From what I've read, it's not that big of a deal. Hey, it hasn't been working anyway, so just to have it smooth will be a big improvement. I'll plug it up and take it for a test ride tonight.
 
Plugging it will fix the lean condition and it will the rely only on the mechanical advance. So some hesitation will still be present.
 
Off idle during acceleration, right? But this should cure the hitching I get at a steady throttle.
 
Yes it should steady it nicely. Keep in mind though you cannot get full ignition advance with only the mechanical advance.
 
It's definitely a lot better! Good enough that I can ride and don't really notice any issues. I can tell it would be better if the vac advance was working but that will have to wait a while.
 
Glad to hear of your good results. Yes it can wait. It's quite the job to replace. Better to ride while the weather is in your favor.
 
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