I have a 327 what I called a detuned 350hp. L79 cam, carburetor and manifold. 194 heads flat top pistons. It would run rough vibrate while standing still through 3000rpm and maybe above. But the other day I plugged the vacuum from the carb to the distributor and also the plugged the distributor vacuum advance pod also. It was running smooth no vibration. And of course when I connected the vacuum lined it started again. Any insight would be helpful.
If the vac advance is connected to full manifold vacuum, try connecting it to a "ported" or off-idle vacuum source instead. If it's already connected to ported vacuum try retarding the initial timing a few degrees.
Will the vacuum advance diaphragm hold a vacuum? Sounds like it might be ruptured causing a vacuum leak.
When I attach the hose to the diaphragm and suck on it (ok no smart remarks) it holds a vacuum and moves the the plate attached to the points.
Some carbs have connections for both ported and full manifold vacuum. Generally speaking, a fitting in the throttle plate or low in the carb body (below the throttle plates) will be manifold vacuum. Fittings above the throttle plate will tend to be ported vacuum.
90% of the engines I’ve owned or worked on idled better and lower on ported vacuum which I have fround to be the stock arraignment. I bought a custom ignition for a HAMB friendly car and engine and told in the instructions to use manifold vacuum. We could not get the engine to even closely idle. Moved to a venturi port and it settled right down and ran much better.
Here's how I determine what timing the engine likes at idle ...... providing the carb tuning is already close. Do a normal warm-up etc, disconnect the vacuum hose and cap off the carb port, loosen the distributor clamp and adjust the distributor +/- until it idles the best. Use a timing light to see what advance is there and then tune the distributors initial plus vacuum degrees to match ..... too much initial will cause detonation at take off. Every engine likes different settings ..... I had a methanol fueled race engine that loved 45 degrees at idle but ran its best speeds at 39 degrees total (locked out). Good luck.
If that's the case, it sounds like the vacuum advance is over-advancing the timing. Most units have some way to limit travel. It's time for a timing light to find out how much the timing is being advanced. My truck had a problem with spark knock on light acceleration due to the vacuum advance over advancing the timing. I put an adjustable unit on and cured the problem.
I checked the initial timing yesterday it was at 17btdc. Awhile back I set the advance timing to 34-36 would this effect the initial timing. I set it yesterday back to initial of 10. didn't set advance. I wish there was a shop around here I could trust or somebody.
Yes, setting total advanced timing will effect the initial. On an engine used for drag racing or high performance operation it may be best to set the total timing and let the initial sit where it lays. On a street engine, low performance use, it may be better to set the initial timing and let the total timing sit where it lays. Go ahead and play around with the initial timing and see how the engine runs best, don't shy away from spending a little time dialing it in. 10* may be fine, 12* may be better. How do you know if you don't experiment with it. In the old days we would bump the timing up 2* at a time and take the car for a spin, find the steepest hill in the area and accelerate up the hill listening for detonation; when the engine starts to detonate accelerating up the hill back the timing back down to the last setting with no detonation.
A degreed balancer, timing light, tacho and adjustable advance/springs capability (mechanical and vacuum) and you have your own distributor machine. The required degree settings are critical but also how quickly and when they come into play. Best performance timing is usually a couple of degrees before detonation (pinging).
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