Vacuum Leak?

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k3522

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Installed 4 seconds flat ignition and distributor this weekend which works great but didn't solve my engine shake in idle. I have discovered once I hook the the vacuum advance to the distributor in idle condition this is when it occurs? If I put my hand partial over the primary on the carb, idle increases about 400 rpm and the engines smooths out. If I hook up a vacuum gage while idling at 800rpm before putting my hand over the carb, vacuum bounces from 8 to 10 because of the irregular idle. I do not want to pull the intake manifold. It has a rebuild AVS by the prior owner. Could this problem be in the carb?
 
have you actually checked with your gauge it is ported? i.e. no vacuum at idle?
just saying what i would check myself
 
Sounds like you are ont eh wrong port. There are two ports on the front of AVSs. One is pass side, I think that's manifold vaccum (has vaccum signal at idle) and the drivers side is ported so it has no vaccum signal aty idle.
 
Could be wrong, but it sounds to me like you have a vacuum leak around the throttle shaft. By partially covering the air inlet with your hand, you are restricting the airflow through the carb enough to make the air leaking around the throttle shaft even things out and you get the correct idle mixture and a nice steady idle. Removing your hand lets it go lean and want to die. See if you can wiggle the throttle shaft up and down and front to rear. If you can there are probably some bushings and a new throttle shaft in your future. There should be next to no detectable movement in the throttle shaft when you wiggle it back and forth. Hope this helps.
 
I checked last night and the vacuum advance is connected to the correct port. I think Grumpuscreature is on to something and I will check the throttle shaft tonight. I think I see a Street Demon carb in my future.
 
I have an FBO distributor and module too and I've had the same symptoms. It's very annoying and frustrating. I haven't really had a chance to try out different things, but I have read that the vacuum advance tube should be connected to the intake manifold with the FBO system and the carb port should be capped. Everyone says connect it to the carb, but FBO says differently for some reason.

I'll be reading this thread to see how you're making out K3522.
 
I haven't read that I should connect to the intake. I did check my throttle shaft and I can move it up down and all around especially on the passenger side end. I may try hooking the vacuum to the manifold.
 
Call FBO...They designed the system, it should be a no brainer. On the worn shafts, I've run soem really bad shafts before...lol. But it is possible that is a partial cause.
 
called FBO and I have a vacuum leak somewhere. I think I will have to get the propane torch out. Can't afford a carb yet.
 
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