Dwell and timing set. Crisp take off and power! BUT rattles on acceleration.

The car is completely stock. It is a totally unmolested engine with 40k miles on it.

I made the following changes.

1. changed intake and carb from 2bbl 73 to Qjet 1970. I rebuilt the carb and blasted the manifold. The carb is totally stock.

2. replaced the points, blue streak something. Once capacitor, one points, one black wire.

3. Distributor and vac advance is stock. Plugs stock part. R45TS gapped to .040 per manual. Vac advance currently on constant manifold vaccuum.



notes

when vac advance is on constant vaccum, it idles much faster. when connected to port vaccum, it idles normal at 650 to 700.

when PCV is blocked, it idles normal at 650-700.


I do get that vacuum advance has no effect at WOT, but there is middle ground before that. What about part throttle when there is some vaccum advance going on and some mechanical advance going on. Is it possible that during the transition the advance can be greater than the total is at WOT and max mechanical advance is present.?

 

so does port vaccum totally go away too at wot?

 

so to use the weak springs you most likely will need an adjustable vaccuum advance correct??

 

if you are on manifold vaccum then your advance at idle will be much more than if you are on port vaccum since port vaccum is not advancing at idle.

Is there any benefit or disadvantage to being advanced at idle? better economy?

all i know is my idle is a lot faster when i have Vac adv hooked up to manifold then when its on port

 

on my gage it says if its in the low end that it means my advance can be retarded. Can retarded advance cause low vaccum?

 

maybe my gage is bad. its very old and doesnt sit down on the zero. it starts at 4" and goes to about 21 or 22 but i subtract the 4 from it to get 17 to 18

 

I run my Vac Advance on ported vaccuum

 

I would run the Vacuum advance on manifold vacuum. There is no logical reason not to.:TU:

 

Yes there is, it's called 4" of vacuum at idle!!!

Not that it applies here, but there's one "logical" reason for you.

Devon

 

In that case how is running on ported better?

 

With my setup now, I don't have enough manifold vac to keep the advance diaphragm engaged. So, I experimanted with ported vacuum this time and adjusted initial advance w/o vacuum advance for a clean idle, then changed mech advance to get my total under control. The ported vacuum at part throttle driving has helped to give it better driving manners and the vac can is no longer confused by the low idle signal it was getting. I had considered not running it at all but kept fiddling with the vacuum source and adjustable vac can until it behaved a bit better.

I don't know specifically why I had to go through it this time around, I changed too much all at once; heads, cam, distributor.

Devon

 

I backed off the initial timing from 10 to 6. It runs better on the highway and punching it down doesnt cause the detonation any more. It has less power from the stop sign though.

I ordered a new vacuum gage, spring kit, and adjustable vaccum advance. Once that gets here I can try to dial iin the timing so i have the perfect advance at the stop sign and not too much total at wot or too much too soon.
Also, got to make sure the vac and mech dont overlap to much creating a detonation spot. Well see, hope i dont blow up my motor.