detonation / knock issue on 340
74 with a 72 340. electronic ignition, will throw a timing light on it tonight and get back to you on that but ive gone up and down. Sound gets worse when i advance it. there is a vacuume advance and it is operating. 91 octane fuel.
This is an excellent idea.
Measure the timing at the lowest rpm it will run, and then write down the rpm for every 2* it advances. Or the other way, every 200 or 250 rpm note the timing. Cap or plug the vacuum advance line when doing this. Write it down. Later on you can graph it.
This will provide critical pieces of information needed for tuning this unknown build.
i was thinking that too, vacuume gauge reads good on manifold and ported. but since spraying the base of the carb and getting the reaction I did ill try the gasket next.
No idea what you mean by 'reads good'.
If you mean vacuum is stable, and that suggests the engine is OK, that's certainly a good sign.
At slow idle, ported should be zero, or at most a few inches of mercury.
In contrast, manifold vacuum can as bad as 4 to 5" Hg on a radical street/strip build, to 16" Hg or more on a stock build.
If the vacuum is really strong at slow idle (650-750 rpm), then engine is less radical and less initial timing will be needed. 12 - 14* BTDC might be a reasonable starting point.
If the vacuum at say 700 rpm is around 11 - 15"hg, then it will need more initial timing. 15 to 18* might be a starting point.
With a Holley 4150/60 set the initial throttle position as shown in the post above here:
Large RPM and Vacuum drop when shifting from park to gear
Tuning for performance procedure outlined here
Setup for 750DP on this 408
Excellent books for 4150/60 carbs is the one by Urich, or the one by Urich and Fisher. You find them used for cheap since they've been in print since the 70s.
