65 flattop 383, 915 heads, stock log manifolds, dual exhaust, eldelbrock 750. MP roadrunner cam. How do I need to know if I need a quicker all in mechanical cruve or a slower one. I have the MP dizzy and the mechanical comes all in at 2k rpm. What is the symptoms of a car needing a faster one verses a slower one?

Have you set the carb up yet? I'd probably start at 36* total the adjust the carb so you get the best idle mmixture/vacuum reading. The re-check the timing. Drive it hard then pump it up to 38* and so on. when the car drops off you should have your ideal tune.

I had it tunned before for maxium vacumm at 750k idle and was pulling 14hg at idle. I borrowed a dail back light only to find out I was at 25* inital and all in at 55* at 2k rpm with the vacuum advanced plugged. It ran and started great. I freaked at the high inital and tuned it back to 8*. Dosent come off idle well I have to feather it and it doesnt start as good. Idle vacuum is now at 10hg. Should I go back to the most vacuum and readjust the dizzy plates to allow only 14* with a higher or lower all in Mechanical rpm?

55* total is high. Leave the vacuum advance un-hooked. You don't need it. Set it so it's around 38* total. Don't worry too much about int advance. You can also buy the MP distrib spring kit. That way it will advance a little quicker. I'm sure JohnRR will chime in. He's good at those stockish 383's

I would set the total w vac adv disconnected at ~36-38 & see where the initial falls at at that point as you always need a fair amount of initial because of a hotter cam always wants more advance depending on the particular cam..all in by 2k is pretty fast & the most important thing is to keep it from pinging no matter what & to ans your q you pretty much want as much adv as you can without it pinging at ANY point in time.When you have that where you want it then hookup your vac adv which can put your total in the 50's under light throttle & it too can be adjusted with a 3/32" allen wrench for the most adv short of pinging under part throttle/cruising(where vac & therefore vac advance)is highest.

So tune it to maxium idle vacuum, Dail back the dizzy mechanical to keep things within 36-40* total and plug the vacuum advance to the manifold port and adjust till pinging at crusing and then back off?