Vacuum Advance

[broncojeep]

I'm no mechanic and I mostly learn by trial and error or getting advice from someone who knows what they are talking about. I was experiencing hesitation and sometimes the engine would die when I accelerated from a stop. A local teacher at the automotive school is a spouse of one of my wife's co-workers. I told him about this and he tested the vacuum advance and said the diagphram was bad and I needed a new one which may help the problem. I got it and changed it and it seems smoother, but the engine is warm, so I need to check it later when the engine is cold to see if it makes a difference.

My question is this...do I need to clean or lubricate the spring and short 'tube?' that fits inside the vacuum port? I'd ask my wifes friend, but he is teaching at school tonight.

[rubiranch]

No lube required.

[Jake11]

The thing you need to look at is the accelerator pump in your carb. Take the air cleaner off and look down in the carb.
Work the throttle arm and see if gas squirts out in two nice streams if it's an "8". One if it's a "6".
Good luck, Jake

[willowbilly3]

Hesitation is generally the vacuum advance or lean (no squirt). It sounds like you are on the right track but to tune the engine right you really need to get the distributor dialed in. That requires a good (dial back) timing light and a hand vacuum pump. I use distributor specs from an old chiltons or motors maunual, they will give the amount of advance at a certain vacuum and also the amount of centrifugal advance (which you really can't change) You can adjust the amount of vacuum advance by inserting a small allen wrench down the vacuum port on the advance unit and adjusting it.

[Jake11]

If you don't have old motors or chiltons, don't sweat it. Mitchell's were the best.
Ball park= 6 to 12deg. inital timing, as in when it's at idle. To little-Bog,s. To much-It won't crank over.
30 to 36deg. @ 2500rpm. with vac. can unplugged. To much and it will rattle. Drive it like that, advance
plugged off and see if it goes and does'nt ping. When you get it to work pretty good, then you can play with
the vac advance. Theres a allen screw inside that you use a 1/8" allen thru the nipple. Keep track and only
turn it a little at a time, like 1/2 turn, or it breaks and you have to buy a new one. Another thing to look at.
The advance in the distributor can and does freeze up. Ck. for that. Jake

[willowbilly3]

30-35 with the vacuum unplugged would probably be too much advance for pump gas. That would make over 40 all in when the vacuum advance was hooked back up. I agree the old books are just a guideline (as is the factory setting) because gas has changed a lot over the years.
Setting it "by ear" is ok if you don't have all the tools but you can get it dead nuts on and have a good baseline for future tuning if you use the factory spec and a dial back light with a vacuum pump. I have had stock engines that were finnicky enough that I only had a 2 degree window to get it right and that takes a lot of trial and error to make that small of adjustment without a good light. The replacement vacuum advance diaphrams are made to fit a lot of different vehicles and I have found few that have the correct setting out of the box.

[Jake11]

I got a "dial" timing light, MAC top of their line. I run 34* on my 390. Regular gas, no pingee.
After a little carb tuning, I get between 11 and 15 at cruise. 70. Between 2500&5000 it screams.
But fuel economy is not so good with foot to floor. I set the can so it just comes on at around
15hg. That way it dumps the advance when give it throttle under load. No pingee and it comes
on at cruise, light throttle. The oid style cans were better. They had a spacer and shims.

Jake

[willowbilly3]

There are a lot of variables but most of the time 35-37 is a good "all in" advance to start with on a stock engine with normal cylinder pressure. All in means all the advance. Usually this is checked at around 2500-3000 rpm on a stock engine.
Factory spec for vacuum advance usually starts in around 5-7 inches of vacuum iirc.