Looking for some tips on tuning

[sharkvette78]

I bought a '78 Vette last May and, after adding some performance stuff, I'm looking to see what you guys have to say as being the best approach to tuning it to get the max out of her.

The engine was rebuilt right before I bought her and it ran great before I yanked it as it was. They put in a performance cam (the guy didn't remember the particulars but it was an edlebrock).

I added a Holley 750 and an intake (can't remember the brand off hand). The Dynomax ceramic headers, mufflers and 2.5" exhaust are going on in a few days.

It runs pretty strong out of gear but getting out on the road, it seems to bog down (even backfiring sometimes) if I get on it hard. I'm attributing this to the lack of the upgraded exhaust. The timing is around ten because twelve is too much when the vaccuum is put back to the advance.

One other question about setting the timing: I disconnected the vaccuum advance when I set the timing and I watched the timing mark move a lot when I gave it gas. Is that normal?

But if anyone has any tips for me or any place online that has good info, let me know. Thanks for the help.

Scotty B.

[Stu Cool]

Scotty,

Your timing advances from two souces, one is vacuum, the other is centrifugal. The centrifugal is controlled by weights inside the distributer that move in relation to engine speed. So even with the vacuum removed you will still see timing changes from the centrifugal when you rev the motor.

As for tuning, it would help to know which 750 Holley you installed and whether your backfires are coming back through the carb or out the exhaust. If it is from the carb, it sounds like you may need a stronger accelerator pump shot. There should be some different holes in the linkage you can play around with to vary the shot from the pump.

good luck

Pat

[sharkvette78]

Stu, thanks for the info. Actually, I stopped by the parts store I frequent and I asked them the same question as I posted about the advance. And when the guy told me about the mechanical one, I remembered all about it. I'm the guy that restores (and learns more and more each time) a ride, sets it up, then never messes with it again because I got it right where I want it. So the last time I had to set up an engine was like 4 years ago. So I forgot a lot of the small stuff.

But I re-timed it this morning and it was like night and day difference. Somehow, after I timed it at about 10 deg BTDC, when I timed it today, it was back to 0. Weird. The dist was tightened down well so I have no idea. I guess whatever it was worked itself out when I re-timed it at 10.

I also used the front-side vaccuum port (the one near the bowl on the passgr. side of the carb) instead of the one on the bottom-front of the carb. That seemed to help a lot since that one only pulls when the butterflys are open.

But thanks for the reply and if you know of anywhere with some good tips on the internet, let me know.

Thanks,

Scotty B.