Ok so i still havent been able to drive the car yet as i cant order the lokar throttle cable until friday, but ive finally got around to messing with the vacuum advance with hands on and i think i finally get it. Tell me if im wrong. So before i started, i had the base timing set at 12 degrees Advance at idle. When I revved the engine to 3000 RPMs I had a 35 degree Total Advanced just like some of you suggested I shoot for. It was perfect sounded perfect. So then I decided to try and hook up the vacuum advance and experiment. I left the base timing at 12 degrees advanced. I had the vacuum advance adjusted to Midway. This was my starting point. When I revved the engine to 3000 RPMs It came up way past 35 degrees advanced. So I shut the engine off and turned the vacuum advance all the way down. I hooked it back up and crank the engine and revved it to 3000 rpms. This still gave me more than 35 degrees Advanced but not as much as before. So then I turned the vacuum advance all the way to the other direction until it stopped just to see. When I revved the engine to 3000 rpms I had probably around 50 degrees Advanced, or something to that effect as it was off the scale. I'm pretty sure that the midpoint gives around 18 degrees Advance over top of not using it at all. So my conclusion is this and tell me if I'm wrong. WITHOUT the vacuum advance 12 degrees base timing will pretty much equal 35 degrees advance at 3000 RPMs which is good. However if I wanted to use the vacuum advance, would this mean that I would need to start with a base timing of 0° to offset what it adds? I'm assuming this is where I would gain the initial Advance if I used the vacuum canister and I would dial that again until 3000 RPMs hit 35 degrees advance. Is this what you guys mean about USING the vacuum advance versus NOT using the vacuum advance? In other words is 12° Advanced only for non-use of the vacuum canister? And 0° Advanced or TDC is used when you decide to use the vacuum canister? Because even at its lowest setting at 3000 RPMs it's still way too much advance with 12 degrees initial at idle. Does this make sense what I'm asking? Thank you.
The vacuum advance is for part throttle cruising under light loads. You can run 45 to 50 degrees total under part throttle cruising, and the engine will love it (better fuel economy and cooler temps). You had your timing adjusted pretty good. Go for at least 10 degrees on the vacuum advance. 0 degrees initial would be even less than the factory spec, and would hurt performance.
Ok this is where im confused then. So i leave it at 12 deg advanced? Fine. When i plug the vacuum advance into the carb the engine immediately runs higher idle and jumps up way past 12degrees. What am i doing wrong here... Or rather what do i do about that? Im using the spark timed vacuum port on the carb, not full manifold if that matters.
I would set your vac pot to give you about 12-13 and leave your initial + centrifugal sum at 35. Test drive it like that and see if it likes it. The amount of advance you see in park when you rev it up will not be the same as in drive when you open the throttle. The vacuum source for the pot will drastically lessen when you open the throttle to actually move the car. So, when you actually drive the car and open the throttle from a stop, all you have is initial. As the rpm come up, you will begin to add to that centrifugal, and as the throttle closes to a cruise state the vac pot will add more. And so, you have advance #s that favor each of the engine conditions. Just make sure you never hear it ping, knock, detonate, whatever you want to call it. I have read opinions that recommend total not be higher than 48, and some say low 50s. I think 48 is safe.
Excuse me, total timing is initial plus centrifugal and not to exceed 36. I dont know what you call the number after the vac pot is added!
It should not advance at idle when connected to ported vacuum (above the throttle blades). Makes me wonder if your idle speed is set high to begin with.
Its possible. What should i have iidle set at in park for auto? Ill set what you advise and move timing to 12adv if needed.
If I recall correctly your engine is a mild built. Curb idle should be between 600 and 800 rpm. Based on Crazy Larry's thought concerning port vacuum's relation to curb idle speed, ensure your carburetor's idle mixture screws are not set too lean with a high curb idle to compensate for the lean mixture. That would create the greater throttle blade opening condition Crazy describes and therefore allowing port vacuum at idle .
Everything that Hotrock and Larry just said, plus if you have A/C, you need to also look at idle speed when that is on, to make sure it doesn't pull it down too low.
I like 800 in Neutral regardless of automatic or manual. I think the factory says 650 in gear with auto.
Wow. Larry and Hotrock nailed it. I had time today to adjust the mixture screws and it was a good half turn to far in on the left side and almost 1 full turn on the right. It settled at 1.6ish turns on each side to give me the highest vacuum reading at 23. The engine runs so much smoother and im still at 12deg advanced with 850ish rpms in neutral. Now when i plug in the vacuum advance i get zero change in rpm at idle. Thanks a ton!
