Anyone running withe their vacuum advance disconnected? I have a stock 318 with a edlebrock performer,1405 carb and 2.5" dual exhaust with X pipe. Recently had the distributor curved and thought I had it running pretty good. I brought it in for a carb tune to the local Mopar "guru",he ended up disconnecting the vacuum advance and set the timing to 12 idle 38 total. It runs good but the idea of no vacuum advance is troubling to me.
Disconnect vacuum advance?
- Thread starter tnpnt1
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Vacuum advance is an economy thing for regular driving. More timing, leaner mixture hopefully better fuel economy.
Some cars won't take the extra timing at cruise. Hook it up, see if it runs OK on the road, no pinging/detonation or surging. Listen close and pull a plug or two, looking for small aluminum flecks of material on the porcelain. If you see flecks, it has too much timing and needs some dialing back.
Plenty of pictures on the net of detonation and spark plugs.
Some cars won't take the extra timing at cruise. Hook it up, see if it runs OK on the road, no pinging/detonation or surging. Listen close and pull a plug or two, looking for small aluminum flecks of material on the porcelain. If you see flecks, it has too much timing and needs some dialing back.
Plenty of pictures on the net of detonation and spark plugs.
4spdragtop
Well-Known Member
You're welcome...
Factory Vacuum Advance Canisters are adjustable. A 3/32 allen key inserted into the hose nipple.
Now the problem is I don't remember counter clockwise or clockwise to increase vacuum or decrease the amount of travel of the diaphragm movement.It can be checked using a dial back timing light.This is if you are experiencing pinging at part throttle.Common when re-curving the distributor using lighter springs.
It is best to use the Vacuum Advance on a street car.
Now the problem is I don't remember counter clockwise or clockwise to increase vacuum or decrease the amount of travel of the diaphragm movement.It can be checked using a dial back timing light.This is if you are experiencing pinging at part throttle.Common when re-curving the distributor using lighter springs.
It is best to use the Vacuum Advance on a street car.
You're welcome...
I was running manifold vacuum prior....thanks though.
What he said ^^^^^^
OttawaCharger
Well-Known Member
Clockwise = less advance
Counterclockwise = more advance
That's actually backwards and incorrect. Clockwise releases tension on the spring and allows the vacuum advance to come in earlier. Counter clockwise tensions the spring and raises the amount of vacuum it takes to pull advance in. The vacuum advance does not control the "amount" of advance. That is a constant. What is adjustable is "WHEN" the advance comes in. You'll want to go through @halifaxhops how to located here:
Vacuum advance information and myrhs
OK where do I start. There is a ton of mis leading information about adjustable Vacuum advances out there. None of the mopar NOS or aftermarket are adjutable for the amount of advance, just the rate of advanc. Yes you can limit them with wire...
www.forabodiesonly.com
OttawaCharger
Well-Known Member
well nuts. Sorry - misremembered. Sorry guys. Here, I just dug up the Moroso instruction sheet for their vacuum advance can.
No worries. Hoppy corrected me on it a long time ago. It just seems common sense that it's the way you described, but once you see a can cut open, it's clear how it works. Thing is, my dumbass has adjusted them for YEARS and I still thought it was backwards from what it was. LOL
I do not have vacuum advance on the Demon. Fast curve in the distributor. Runs great and gets pretty decent mileage considering.
Ant
Well-Known Member
Avoid anyone who claims to be a "guru" in anything.
Ain't that the truth?
NC Engine Builder
Grumpy Old Man
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Your mileage would ABSOLUTELY increase with the proper amount of vac advance.
I assume it will, but once I got it dialed in and running so good, I won't change it. 440, tunnel ram and 660 center squirters. Still got 12-13mpg over a 250 mile drive each way in June
Ant
Well-Known Member
True.
I Had an old Mercedes with the Bosch K-jet mechanical fuel injection and a mechanical vac advance distributor. I tuned it for the maximum amount of vacuum I could get and under low rpm load, it got the most timing advance it can get before the fly-weights took over. That car ran like a champ, still a little slow, but still a champ on 87 octane gas.
OttawaCharger
Well-Known Member
Useful pic Halifax. I'm going to save that one 
I agree to use the vacuum advance on one or the other vacuum sources unless your camshaft is large by huge and then the vacuum won't amount to much. Even on my slant 6 with only 6hg at idle and a max of 14 going downhill in a tail wind it does help.
Dartswinger70
Well-Known Member
And smarter than the average bear!
abodyjoe
Well-Known Member
un hooking the vac advance didn't change the curve any. if the vac advance was hooked up correctly it wasn't doing any thing at idle and wasn't doing anything when at full throttle.. thats all mechanical. vac advance is activated more at cruising speeds. 38* seem like a lot of total. but every car is a bit different i guess.
It was running at 17/51 before from what he said,I never verified total myself.
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