General Category > Quadrajet Carb Talk and Tips

APT adjustment question

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tayto:

--- Quote from: Greasy Harley on April 28, 2021, 10:01:00 PM ---I think I got it. I turned the APT down 1/4 turn at a time 'til I got light detonation with the Vacuum adv, then I turned it up just over 1/4 turn. pulls hard, no detonation, no stumble.
I am still unclear what I was doing wrong during the tip-in procedure.
I am doing something wrong. The adjust and test method works, but it takes a lot more time.
Anybody have a link to a good tip-in procedure video?

--- End quote ---
i have a similar engine build to yours.what octane did you end up running? how much mechanical and vac advance does your engine like?

Greasy Harley:

--- Quote from: tayto on April 29, 2021, 08:08:28 PM ---i have a similar engine build to yours.what octane did you end up running? how much mechanical and vac advance does your engine like?

--- End quote ---
I run 91 octane 10% ethanol
Timing is set at 13° initial-33°all in
Sometimes i get a bad batch of gas and get a little pinging with the Vac-adv plugged in, so I just leave it unplugged. Makes my life easier.

Glutenfreecarbs:
I ran TBI/swirl-port heads with a Q-jet for a few years, and my final recipe was 8° initial, 15° vacuum advance, and 16° mechanical advance, for 24° total at WOT. I used Mr. Gasket's "medium" distributor springs, and an Accel adjustable vac advance cannister, modified with an external spring to make it start pulling timing at around 10 inHg manifold vacuum.

Don't listen to the old-timers that say "every SBC wants 35° total timing." I've got two burnt head gaskets hanging on my wall that suggest otherwise...

tayto:
TBI heads like 25-30* total timing.My engine made the most power with 26* total. had to convince the dyno operator to go down from 32* instead of up i can post dyno sheets later.

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