Mechanical or Vacuum Advance. Which one?

[1971RR]

I have a 1971 RR Clone. Current setup is 383, probably close to stock build, 727 and a 2.76 rear 8-1/4. I have been have a Mallory Unilite, 3757701 and an Edlebrock 1406. Now, when I installed the new Edelbrock and took her for a spin, she ran great. Pulled past 5K RPM with no problems. I was surprized because it had been falling over a bit after 4200 and generally becoming just a noise machine after that. I was happy. However, I was having starting issues, mostly after warming up. I checked my stock distributor and noticed that the vacuum advance was not functioning. I had the above mentioned Mallory (mechanical advance BTW)sitting around from about 20 years ago and dropped it in. Now the car didnt have the power it had experienced with the factory distributor and it went back to falling over at around 4k RPM. The starting issues seemed about the same. I thought maybe it was vapor-locking as the fuel filter would become empty, but you could still see the gas spurting into the filter as the car was running. I had modified the distributor with a GM advance kit but put it back to stock. I'm getting a little frustrated trying to figure this out. A couple things I do know. I have the wrong plug wires. They are copper core which Mallory states to use carbon core. My ballast may not be the best. I dont really get a true 12V on either side. I assume the right side, facing the engine, is the 12V input side. Its mounted on the firewall. I've got the distributor grounded to the innerfender and the red (hot) on the "+" side of the distributor (I've also run the hot to the 12V side of the ballast but it doesnt run any better or worse and Mallory really wants it on the ballast). I really would like to continue with the electronic ignition but I'm not sure if a mechanical advance is a good choice for the setup I have. Opinions? I was considering getting a curve kit for the Mallory and experimenting or just getting a 4757701 which is basically the same distributor but with vacuum advance. I'm not really adept at tuning this thing as I once was but I really want to get this right. If I do go the curve kit route, does anyone have any suggestions for the curve? Linear? "Hop-Out"? RPM range? Any help will be appreciated.

 

[lewtot184]

if your going to drive a bunch use the vacuum advance.

 

[67 coronet]

vac advance is normally better for street use.also the malory has a plastic key that(when inserted and adjusted)will set max advance.yours may be too low.its also not a good idea to run full 12 volts to a unilite you might blow out the led module.

 

[Don Gould]

If the motor makes 10" or more manifold Vacuum, the Rule of Thumb is that it should have a Vacuum Can.

71RR-Email me a Direct request referencing this post and I'll send you a Free Email version of my 47 page Tuning Guide which will explain why. [email protected]