Pontiac GTO Forum - View Single Post - Exaust backfiring
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post #60 of (permalink) Old 04-13-2019, 04:01 PM
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Originally Posted by PontiacJim View Post
cij911 - "I have been told by someone far more experienced than me that my current setup has a base timing too low and that I should be more like 16* + 10* vacuum canister which would yield 26* at idle with vacuum and that I should get a distributor with 20* mechanical advance."

PJ - You might want to let this guy have your car and let him set it up for you.

You have been given the correct info by Lemans guy as well as TheGoatFather1965 and don't seem to want to take their advice and I am not sure why not? If you talk to 100 people you are going to get 100 suggestions - only adding to your confusion.

Maybe you want to start from scratch. Pull the distributor and do a rebuild. Check the gear for wear and endplay. Then go from there. With all this difficulty, I'm thinking you have a bad/worn distributor.
PJ - He is not local, otherwise I would. He is super knowledgeable and very helpful. That said, I am trying to learn from those of you with more experience.

The distributor is NEW and there are NO problems with it, just that the vacuum can it came with has too much advance 25* vs recommended 10*. Additionally it appears the distributor has more mechanical advance than ideal - 30*, which has my base timing at 6* to get a total advance of 36* coming in before 3500. The car as it sits runs well and pulls hard.

What I am trying to understand is why changing the distributor would help. Basically the recommended setup has base at 16* (vs my 6*) and a 10* vacuum can so at idle it would be 26* (vs. my setup at 31*). My understanding is if a car runs well at 31* (vs 26*) it is even better as it will run cooler at idle. At WOT, I am at 36* (just as the recommended), so really no difference there.

So basically it comes down to partial throttle and transient response (which is a major part of normal driving). My question is am I likely running too much timing? While the recommended distributor has base timing 10* more than mine, I feel that is really a meaningless (as described above). So maybe the concern is I am running too much timing mid rpm range with modest load ? That I could understand, but I am unsure if that is true as I haven't seen any signs. Basically I guess the car could see as much as 51* (full mechanical + full vacuum) vs. the recommended setup as much as 30* (full mechanical of 20* + full vacuum of 10*). So is that the issue ? And if so, what would I see / hear / or feel that would indicate it was too much? (I haven't heard pinging, car feels responsive, and stays under 190* under the hardest driving.)

Thanks for the help.

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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