Would low vacuum be a reason to run a mechanical advance distributor?

 

No.

 

That's an odd question, but the answer is no.
Are you having problems getting the car to idle and the vacuum is low?

 

Yes, the car has low vacuum because of the cam (we eliminated leaks). I've been dealing with this for a while. The carb guy says that I should run a mechanical advance distributor since I have little vacuum. He said I could get the timing the engine needs that way. I am not a mechanic but I am trying to understand all of this. I will try to have the car timed correctly tomorrow according to the cam card and see how it runs. As of right now, the car has no low end power, however, it does idle better since we advanced the timing, but the vaccum port is up against the manifold.

 

I would get a vacuum resevoir first to see if that clears it up. How low are you? Also, SSBC makes a vacuum pump that is electric and runs to keep the system vacuum at 18". I'd personally do that before ever considering swapping a distributor.

 

What distributor are you running now that it doesn't have an advance?
If you are running an msd distributor install the black advance bushing, reset the total timing back where it was and that should give you more timing at idle. (total timing minus 18 will equal idle timing). Also if you have a vacuum can on the distributor hook it up to full manifold vacuum. That will give you a big increase in idle timing and help smooth things out assuming the carb is adjusted right.

btw what size is the cam?

 

Sounds like it's already got a standard mech + vac advance dist, if it's the type with the vac can?

Edit: If you can't get more timing (sounds like it needs it), because the dist won't rotate any further because of the vac can hitting the manifold - just pull it and rotate a tooth clockwise.

 

Also, if the timing's too retarded it would explain the lack of power and vacuum.

 

That's what we're going to do tomorrow. Pull it, reset it, and go from there. The cam is a .230/.230 .480, 108 LSA. I think the vacuum gauge said 7, but I couldn't see it correctly. My brakes work good, though.

 

If that cam is in a 350, it's not a real good choice especailly for a street motor, being an old Stone Age design and all; but should have around 12-13" of vac at idle.

Sounds to me like the timing is AT LEAST 10° retarded from where THE ENGINE (as opposed to "the light") wants it to be.

Just for a rough test, advance the timing unti it just starts to ping, then back it off til it just quits. Won't be "right" necessarily, but will find WHAT THE ENGINE WANTS; should give you a pretty good idea of how BAD OFF "the light" method is.

If THE ENGINE and "the light" disagree, believe THE ENGINE.

"If it RUNS good, it IS good". If it DOESN'T run good, then, .... doesn't too much matter whether "the light" is happy or not. Eh??

 

Got it timed (35 degrees total) and it seems to run well and idle great, no low end bog or sputtering. However, I noticed 2 things. The car now seems to struggle to turn over. The guy at the shop stated this was normal with the current setup. Second, when cruising in drive or OD, there is a sputtering. Almost seems like the engine is skipping. Could this be a matter of tuning the carb? I don't know any specs on the carb, other than being a Holley 750 DP, vacuum secondary. I got it from the carb shop, so I could ask him what's in it if need be. I wanted to run it by you guys first. Thanks for all the help.

 

Starting: Despite it being what the engine wants - now sound's like you've got too much initial timing for the starter to comfortably handle. Back if off a couple of degrees and see if it gets easier.

Surging: Was it doing this before you set the timing to where it is now? Sounds more like a carb thing - vac leak, carb a little oversized (low venturi signal with butterflies nearly closed), idle mix adjustment etc.

 

It seems a little strange that the timing is to high at idle to start smooth with 35 total. And the hard starting is not normal as stated by your mechanic.
You never answered me last time, but what distributor do you have and what springs are in it? Also do you have vacuum advance and if so what port is it hooked up to?
And how old is your balancer? Its possible that the outer ring on it spun and is causing you timing marks to be off.

As far as the surging, its probably the carb is way out of tune. But it can be the timing also, so its important to get the timing right first before tuning the carb.

 

Not many of us are - professionally, anyway.

But, given these statements:
I'd say he isn't, either. Or, at least, not much of one.

Maybe I read through too fast, but I didn't see what distributor you have. Sure sounds like a vacuum/mechanical advance HEI, but...

Here are the basics: You set the mechanical advance to give best power. You can either do that with a dyno, or you can get it in the ballpark with the vacuum disconnected, run the engine RPMs up until you get mechanical advance (there's another way to do that, but I won't complicate this with that info), then set the timing to 34-36 degrees BTDC (assuming your timing marks are accurate. As sofa indicated, you can adjust from there to give the engine what it wants (did I mention a dyno?). If, when you have that set where it should be, the starter "kicks back", then you have too much mechanical advance at start/low RPM. You can either increase the amount of mechanical advance the distributor has (whole 'nuther topic), or artificially reduce timing during starting (there are a couple of ways to do that).

The vacuum advance is primarily for cruise conditions. It can also improve idle, but if you have low idle vacuum because of the cam, it won't help much (and a vacuum reservoir is NOT a good idea). You will have more vacuum at cruise than you may have at idle with a high-overlap cam, so it may still help for better fuel economy, even if it doesn't do much at idle.

 

The distributor is an HEI vacuum advance (Proform). Don't know what springs are in it. It is connected to the front lower port on the carb.

No the car didn't surge before the timing was adjusted this time.

The balancer is brand new (Professional products).

So. I should retard the timing a slight amount to see if my problem is corrected?