|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: IronWolf]
#126413
09/29/08 05:19 PM
09/29/08 05:19 PM
|
Anonymous
Unregistered
|
Anonymous
Unregistered
|
Quote:
Quote:
Back off the initial timing. Should be 12-15* with the vacuum advance disconnected. Then hook the advance back up.
This response is correct. Unless you do NOT care about fuel mileage. Listen to the man.
This is one of the generallizations that gets folks into trouble, IMHO. In many cases it is correct, but it can also be incorrect. It all depends on the setup. If the distributor is setup for TDC base, you can cause a bunch of problems. I totally agree with the 10-12* being good at idle, no vacuum advance, but if you do it at the 10/12, you need to be sure that the distributor was setup for it, so the rest of the curve is right.
If the distributor was setup to be timed at TDC, like many were, you need to take out the extra timing when you advance the base setting. Most people remember to change the mechanical advance to limit total to 35* or whatever number works best on your combo, but they also bring it in earlier than it was originally. Under marginal fuel conditions, the extra mechanical will give you the low rpm ping, when you have vacuum advance on. You can either bring in the vacuum advance later (vacuum wise) or go to a can that has less advance in the can or a different rate of advance. One thing to be very cautious of is that if you have audible ping at low rpm, you very well may have it at higher rpm, low loads, also, but it is inaubible. You need to read your plugs for signs of detonation after a low load run down the highway to see what is going on with detonation.
It is also possible that the low rpm, low load ping is caused by a lean condition in the carb as it transitions to the main system. this usually happens at just about the time the vacuum advance comes in. This is very common, but is be relatively easy to tune out with most carbs.
The computer progammable spark curves that are available now can be a wonderful thing, as you can tune out all of the oddities, keep you performance, and not have to sacrifice efficiency and mileage.
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: BergmanAutoCraft]
#126414
09/29/08 05:24 PM
09/29/08 05:24 PM
|
Joined: Jan 2003
Posts: 5,791
Hamilton, Ontario Canada
Magnum
master
|
master
Joined: Jan 2003
Posts: 5,791
Hamilton, Ontario Canada
|
Quote:
One thing that was said that I did not agree with was the part about manifold vacuum going to zero when the throttles are open. Unless the throttle is fully open, vacuum usually hangs around 1"hg...Secondly, I have found vacuum to increase at light throttle in many cases, which can make the engine ping, which is why many people get rid of the vacuum advance all together. Different engines do like different things, very true.
1" of vacuum will not affect the vacuum advance. It needs around 10" to move.
If you are pinging at light throttle you need to either limit the amount vacuum advance by lengthing the stops. Or tightening the spring inside the cannister with a 3/16" hex key.
Lastly. I usually trust the engineers, even though this was 40 years ago. But not all of them were that smart. Remember it was one of them that decided to run our full electrical load through a bulkhead connector and an amp meter in our dash.
Another one of them liked negative caster too. 
Last edited by Magnum; 09/29/08 05:26 PM.
69 Super Bee, 93 Mustang LX, 04 Allure Super
|
|
|
|
|
|
|
