Technical Distributor and Timing Questions

Try one light spring and one medium spring.

 

Here you go

 

Because Chevy was smart enough to put the oil pump and oil pan sump at the correct end of the engine. The fact they planned to use the distributor to drive the pump then made the distributor location what it is.

Yep, try this step.

 

I had a petronix distributer in a ot truck. It is a piece of shit I kept breaking rotors. it was shimmed incorrectly from the factory and wore out quickly. went to the junkyard and bought one and it has been in for over 100,000 miles.

Denny

 

"Vacuum advance" again. The only way it advances is on 'spark ported' outlets that read an increase in vacuum as RPMs go up. On manifold vacuum it will retard the timing when vacuum drops at the opening of the throttle, making it a load compensator reducing pre-ignition. Both can be a great tool for dialing in overall timing on a high zoot street engine.

 

^^^^^^ This is kinda off in several ways "ported vacuum" is picked up at the throttle blade and the port is exposed to manifold vacuum when the throttle blade(s) open(s). This vacuum acts on a diaphragm which advances the spark advance from the point where it was set mechanically with the vacuum line disconnected and plugged. If the throttle is opened quickly the manifold vacuum drops and spark advance retreats towards it's non advanced position to correspond with the reduced manifold vacuum. This ported vacuum doesn't advance spark til the carb is off idle and exposes the vacuum port just below the seated throttle blade(s).
Manifold vacuum works much the same, except there is vacuum possible according to load at any time the engine is running, including at an idle. Either of these systems function along with mechanical advance from flyweights in the distributor.
The "Loadamatic" advance system used by Fomoco from 49-56 utilized venturi vacuum picked up from the downstream side of the carb venturi(s) as the carb throat ID @ the venturi expanded back to throttle bore ID at throttle blade(s). This was THE ONLY ADVANCE SYSTEM USED IN THESE DISTRIBUTORS. The theory was that the increased air flow as engine rpm increased would increase the venturi vacuum and advance the spark via the diaphragm, and that increased load and consequent wider opening of throttle vs rpm would decrease venturi vacuum, and allow springs to pull the diaphragm back to less advance. This system worked but not too well.

 

Are you sure the bushing is in the right place? I would think the bushing would be in the weight not on top.

 

Too large in diameter to be in the weight. I assume it is just there to maintain the space between the weight and the spring. I looked online and the advance curve kits that they sell for Pertronix have the weights, springs, and some little plastic bushings that look like they are supposed to go in the weights. When I have an opportunity to get back out to the garage I am going to take the other weight off and see if it has a bushing on the bottom side. That would certainly explain the slop.

 

I appreciate the conversation, but you missed that I said "SPARK PORTED" which is a vacuum port that increases vacuum as RPM (carb flow) increases. On things more modern than you mentioned it can be found higher up on the carb, and no, not every carb has the option to do that. And yes, most every carb has a manifold vacuum port down near the blades or simply in the base plate.

 

That bushing may be to go on the pin under the advance plate to limit the mechanical advance.

 

I finally got a chance to get back to this(business and family stuff has been super hectic). I pulled the other advance weight off and there was nothing visibly different on the side that was operating properly vs the side that had the slop in it's movement. I swapped the weights side for side and determined it must be an issue with the distributor and not just the weight because the slop is still on the same side. So, I bit the bullet and ordered another distributor last night.