Holley stumble trouble
A 2 bbl 318 is pretty efficient combustionwise at low rpms.
Your engine obviously gives that up, but probably dvelopes good efficiencies by 2000 rpm.
Any time using the vacuum advance, the mechanical advance has to be darn close.
For drag racing, the quick in is OK with no vac advance. The engines don't get heat soaked and actually may work better; and at WOT the vac advance is just one more thing not needed.
Anyway. here's a couple of timing plots using the specs from the plymouth shop manuals.
Compare with
We can see the 318 needed around 16* lead at 1400 rpm where as the 273 power pak needed arond 24* at 1400.
More important for your issue, notice how in both cases the rate of advance is reduced above 1400 rpm.
Why? Because these Chrysler engines (and others too) combustion speeds up as engine rpm hits a range where it has better efficiency.
The second spring should have a loop on one side. That length of the loop and the spring perches determine how many degrees into the advance before it starts to restrain the weight.
While we can't do this with many non-chrysler distributors, its not such a big deal when initial timing is around 20*.
the mechanical advance handles lead time needed for rpm.
Vacuum advance handles lead time needed for low density (leaner and slower burning) situations/
My interpretation of the 273 4 bbl vac advance going as low as 5" Hg is that it the engine had good part throttle fuel distribution.
I would generally like to see a vacuum advance that is out of the picture about the same vacuum as the power valve opens.
The logic here is that the power valve is enrichment and vacuum advance is for lean conditions.
I don't know what distributor you started with.
A 2 bbl 318 is pretty efficient combustionwise at low rpms.
Your engine obviously gives that up, but probably dvelopes good efficiencies by 2000 rpm.
Any time using the vacuum advance, the mechanical advance has to be darn close.
For drag racing, the quick in is OK with no vac advance. The engines don't get heat soaked and actually may work better; and at WOT the vac advance is just one more thing not needed.
Anyway. here's a couple of timing plots using the specs from the plymouth shop manuals.
Compare with
We can see the 318 needed around 16* lead at 1400 rpm where as the 273 power pak needed arond 24* at 1400.
More important for your issue, notice how in both cases the rate of advance is reduced above 1400 rpm.
Why? Because these Chrysler engines (and others too) combustion speeds up as engine rpm hits a range where it has better efficiency.
The second spring should have a loop on one side. That length of the loop and the spring perches determine how many degrees into the advance before it starts to restrain the weight.
While we can't do this with many non-chrysler distributors, its not such a big deal when initial timing is around 20*.
the mechanical advance handles lead time needed for rpm.
Vacuum advance handles lead time needed for low density (leaner and slower burning) situations/
My interpretation of the 273 4 bbl vac advance going as low as 5" Hg is that it the engine had good part throttle fuel distribution.
I would generally like to see a vacuum advance that is out of the picture about the same vacuum as the power valve opens.
The logic here is that the power valve is enrichment and vacuum advance is for lean conditions.
