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Old 29-10-2017, 02:30 PM
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cluxford cluxford is offline
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Has my vac advance died

Just general tune and I noticed that my initial timing is 16 degrees at idle regardless if vac advance is connected or disconnected. Itís connected to manifold vac. Timing stays st 16 degrees no matter if connect or not. Broken can ?
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  #2  
Old 29-10-2017, 07:38 PM
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bonnevista bonnevista is offline
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Either the can is broken, or there's a crack in the vacuum line. The cans do go bad. Keep in mind how much work the canister does over the years. The diaphragm will fail eventually.
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Old 29-10-2017, 08:34 PM
Geoff 4 Geoff 4 is offline
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Another possibility is the VA has frozen up over the years. Remove the dist cap [ & rotor for a better look ] & suck on the VA hose. If you can suck air, either the hose or the can is leaking. If you don't get air when you suck, the mechanism might be stuck. Prod the VA actuator with a screwdriver to see it moves. Might just need some lube...
If it is a MSD Ready To Fail [ er, sorry Ready to Run ] dist, they use a plastic bush for the actuator rod that can bind.
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Old 31-10-2017, 05:55 PM
qik66 qik66 is offline
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Chris
easiest thing to check is that you are getting vacuum at the hose, it has been a long time since I have had anything with a vacuum advance but doesn't it come in until you start to lift the revs, bring the revs up to about 1500rpm and then with the timing light on pull the vac line off and on, if all working the timing should advance and retard as you do it.
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Old 31-10-2017, 06:41 PM
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cluxford cluxford is offline
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Thanks Neil. Will do that tomorrow. I have a new one just in case
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Old 31-10-2017, 06:59 PM
Geoff 4 Geoff 4 is offline
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He says he has the VA connected to manifold vacuum [ Gold Star awarded ] , which means there should be vacuum at idle, no need to rev the engine.
Modified engines that are using VA should be using manifold vacuum as the source, not the useless ported vacuum.
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Old 31-10-2017, 07:28 PM
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yep it is to manifold and I have checked it with engine running but not revving it, easy check so will do it. I'm almost certain the can is dead, car is running like a POS, super super rich and fouling plugs on right hand bank, low rpm miss, fine at high revs, bit of a surge at idle, suggests a vac leak consistent with vac advance can dead
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Old 01-11-2017, 07:16 PM
Geoff 4 Geoff 4 is offline
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Chris,
If you need some help, PM me for my phone #. I helped Blackout Steve [ R.I.P.] get his Chev idling better after a discussion with him about MVA [ Man connected Vac Adv ].

Great advice here on MVA by retired GM engineer Lars Grimsrud:

http://www.hotrodders.com/forum/vacu...bad-47495.html

scroll down to post #6.
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Old 01-11-2017, 07:36 PM
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All good old one stuffed new one in today purring like a kitten. Having 2 plug leads arching on exhaust also did not help. Buggers were only 2 weeks old. But they are also replaced now
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