Vacuum pop
 

Hey I finally got the car back from the body shop (would much rather not re-live my ding-up :) Anyway, I am ready for the out of province inspection, but I have one last concern. From a dead stop I have to tap on the gas multiple times to slowly get it going, instead of pressing it normal. If I press it regular from a dead stop it will "pop" and the car will likely die. There is a brand new carb and it has been tuned so this shouldn't be the issue. My mechanic/friend and I have gone through all the possible vacuum leaks, but there were none. My mechanic said there is somewhat a lumpy cam in there (I don't know what it is), which could be causing the motor to have a low vacuum, and he suggested that I get a vacuum advance that engages at 6-7pounds. I did look, but anything I saw is a regular vacuum advance that doesn't specifically tell when it engages.

Otherwise we are running out of option. Could the pertronix electronic ignition cause this? I am just throwing out some random suggestions. And does anyone know what brand of vacuum advance there is that I could snag, which is what he is talking about?

Ultimately, the issue is the vacuum is low on this beast, but there are no vacuum leak issues on the car, and it sucks

Sounds like a base timing issue or crossed spark plug wire to me

Spark plug wires are all correct....this has been checked by myself and 2 other people.

The base timing is set at 8. I don't have it on me right now, but I think this is correct. It sucks that I am so close yet so far

The carb may be new but it sounds to me like the accelerator pump may not be working right. With the engine off slowly open the throttle while looking into the primary bores. You should see two strong steady streams of gas squirt in as soon as you start opening the throttle. If there is a delay before you see flow or the streams are weak then you have a carb problem.

If you can get a vacuum gauge and report back with actual idle vacuum reading it will help. Also if you check the timing at idle with the vacuum connected to your existing vacuum can, and then with the vacuum line disconnected, the difference in the readings is the amount of advance you are getting from the vacuum advance.

The base timing at 8 degrees is quite a bit lower than most of us run but it depends on the particular engine combo and how much centrifugal advance the distributor has.

^^^ I was thinking the same thing. I've seen several new accelerator pump cups go bad with today's fuel.

At idle the vacuum is at 10.

I will take a peak tomorrow at the carb and get back to you

My base timing is 14 & my total is 36. I think your accl. pump is your first problem & then your timing & advance.

Just checked the accelerator pump works perfect.

So I know there is no 100% sweet spot for timing, especially since there is a lumpy cam that we don't know what it is, but I guess I will adjust the timing and cross my fingers.

I turned the timing up to 14 and the car is much much better. I can now mash the pedal down without it stalling. From a dead stop 99% of the time I could mash the pedal with no issues, one time it did make a "pop" and one other time it stalled (these were both times that I was turning...if that has anything to do with it or is just a coincidence).

There is still some slight hesitation at times too, but still thousands of times better

My bet is that by advancing the distributor you picked up significant vacuum at idle too. As long as you do not hear any pinging I would go with 14 for now. There are a lot of threads in the street section on how to set up the distributor and timing curve to get optimum performance.

I went for another rip and I am sure it is not my imagination anymore. I can stomp it from a stand still with no iss when going straight, but it died twice when stomping it while turning right and left. Does turning put more of a load on a motor then going straight? Now that the main issue is taken care of, is there something I should look at to solve this?

You are checking the base timing with vacuum disconnected to the distributor and plugged aren't you?
I agree that 8* initial mechanical timing is low...Back in the day when these cars were running higher compression and the initial factory carb setups, that was about right and I believe the specs called for 9* advance timing.
I'm at 14* initial myself (mechanical) at about 900~950 RPM with no vacuum attached. Mechanical advance starts to come in at about 1250 RPM with max mechanical advance about 34* at 2800~3000 RPM.
You can purchase an adjustable vac advance can. I have mine set up also at around 10*~14* so in actuality, at idle with vac advance and initial advance combined, you'll see something like 24~28* ....but I always look at mechanical and total first, then you can tweak the vacuum advance where you want it.
Remember, the vacuum advance is gone by the time those higher RPMs are reached so mechanical advance sort of 'replaces' the vacuum advance by then....but does not add to it.

I think you got very good advice on the timing, but will throw in another wrench. When I had the tripower on mine, it would die when turning too fast and if I remember right when hitting the brakes too hard. The carbs were dumping gas under those conditions. I had to adjust the floats slightly lower than the rebuild kits called for, but it solved the problem.

Crap, I adjusted the timing with the vacuum advance still plugged into the carb. Dammit...I can change this easy, but what does this mean, just for knowledge sake.

It means your timing is set way too low. Disconnect the hose and plug it with a golf tee, screw, or just hold your finger over it and re-adjust the timing. I think you are going to be very happy with the results.

That is actually good news. When you adjust it correctly (without vacuum advance) you will likely find that the engine really comes alive!

Yeah, if you set it at 8* with the vacuum attached, you are probably set 5 or 10 degrees RETARDED rather than 10~12 advanced. WAY too low.

When it was tuned at 8, it was properly with the vacuum advance plugged. I just didn't plug it when I turned it to 14, but still glad it's good news :) The driveability was really preventing me from wanting to do any further work on it because my spirits were crushed

Gotcha.....at any rate, you should be on the right track now.