Idle hanging up with vacuum advance hooked up - Team Camaro Tech
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post #1 of 9 (permalink) Old Nov 24th, 09, 10:33 AM Thread Starter
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Doug
 
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Idle hanging up with vacuum advance hooked up

With my vacuum advance hooked up my carb will hang up at 1,000 rpms and then settle down to 700 rpms. If you unplug the vacuum advance there is no problem. Seems like it's holding vacuum. It also has a pertronix pointless ignition and coil. Any ideas.
Thanks in advance
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post #2 of 9 (permalink) Old Nov 24th, 09, 10:40 AM Thread Starter
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Re: Idle hanging up with vacuum advance hooked up

Should have added - Small block 350 , 1969 with quadrajet carb.
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post #3 of 9 (permalink) Old Nov 24th, 09, 10:57 AM
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Re: Idle hanging up with vacuum advance hooked up

Check the VA canister is not leaking or sticking
check leaking bu sucking on the tube and see if it hold vaccuuum
Check sticking...remove cap, suck on in then slowly and quickly release vac....put your finger on the actuation lever and feel the movement.

My Spelling is not incorrect...it is creative

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post #4 of 9 (permalink) Old Nov 24th, 09, 11:40 AM
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Re: Idle hanging up with vacuum advance hooked up

You're experiencing the "lack of vacuum blues" due to cam, most likely!....The motor doesn't have sufficient vacuum to properly work the vacuum advance canister!....I had the same prob in my 327 when it had a big hairy cam in it which only pulled 7"Hg vacuum at idle....You could try using one of those adjustable vacuum advance canisters!
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post #5 of 9 (permalink) Old Nov 24th, 09, 05:15 PM
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Re: Idle hanging up with vacuum advance hooked up

Vacuum advance will raise your idle speed. That's one of the advantages of vacuum advance - the engine runs more efficiently with a bit of advance at idle. Your base idle speed should be set with the VA connected. Vacuum leaks can be exaserbated by the VA timing advance. VA increases idle vacuum slightly.

Also be sure that the mechanical advance isn't kicking in too low. You'll have to do this with a timing light and the VA disconnected. Run the throttle up and down by hand and determine where machanical advance picks up. If it's coming at at low speed (like 1000-1500 RPM) can can really foul up your idle speed and make the idle act inconsistantly.

Dave
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post #6 of 9 (permalink) Old Nov 24th, 09, 06:21 PM
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Re: Idle hanging up with vacuum advance hooked up

It is important to match the VA can for the vacuum figures on your engine. Best to read JohnZ's articles on vacuum advances. It specs out a bunch of cans at the end.

http://www.hotrodders.com/forum/dist...1-a-59033.html

alan
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post #7 of 9 (permalink) Old Nov 24th, 09, 09:54 PM
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Re: Idle hanging up with vacuum advance hooked up

Good point on teh VA match up. I've got a crane adjustable VA. I set the full advance to just a fuzz below full idle vacuum. There is also a cam washer that limits the full advance setting.

Dave
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post #8 of 9 (permalink) Old Nov 25th, 09, 06:11 AM
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Re: Idle hanging up with vacuum advance hooked up

[QUOTE=dnult;Also be sure that the mechanical advance isn't kicking in too low. You'll have to do this with a timing light and the VA disconnected. Run the throttle up and down by hand and determine where machanical advance picks up. If it's coming at at low speed (like 1000-1500 RPM) can can really foul up your idle speed and make the idle act inconsistantly.[/QUOTE]

Dave, how would I know when the mechanical advance is kicking in?

Steve
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post #9 of 9 (permalink) Old Nov 25th, 09, 06:57 AM
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Re: Idle hanging up with vacuum advance hooked up

Well, you put on a timing light with the VA disconnected. Also, connect a tach-dwell meter to the distributor side of the coil (left or right terminal, not the high voltage terminal). As you increase the rpm, the timing mark will move. The rpm where the mark starts to move is where the mech adv. starts to kick in.



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