Okay, we learn everyday right? Well, its my turn. Up until now, I have always set timing by vacuum reading. Just turn the dist. until you get the highest reading. It has worked for me for quite some time. Well, it stopped working like it normaly use to today. I have an adjustable vacuum canister, and when I switched to carb, the tech article about the switch gave a baseline of 9 1/2 turns out on the screw to start. I got a dial back timing light from my neighbor to use. The initial timing is 10*, with the vacuum hooked up to a ported source on the carb, the total is 45* in by about 2500rpm. Now I thought I wanted 32* total, mainly due to the buildups I have read using Vortec heads, that was pretty much the norm. I turned the canister screw in a lot. Didn't count how much b/c I planned on turning until it ran better and not worrying about how many turns in/out it took. When I unhook the vac. adv., and try to rev the engine to check timing it pops back through the carb real bad and doesn't want to run. As it sits now, with the vacuum hooked to ported source, at WOT the cars breaks up real bad. Doesn't pull very well, and just plain sucks. My question is: what does the adjustment on the canister allow me to do?, and what can I do to keep 10* initial, but 32* total. I don't know what the number is on the canister. I do remeber that being something needed to help more. Any help, critisism, whatever is welcome. I just need to know more about the vacuum advance of a dist.

Thanks,

 

34-36 degrees is the total mechanical advance at higher RPMs, checked with the vacuum disconnected.

You adjust the vacuum canister to avoid part-throttle loaded pinging. You are adjusting the spring force against the diaphragm to change the vacuum it takes to produce a given advance with the diaphragm, not the amount of advance possible.

 

So the canister adjustment pretty much controls the rate of advance? Is it normal to run crappy with the VA unhooked while setting the total mechanical advance? If I want 10* initial, and 34-36 total, and say I'm at 40 total mech. adv., do I need a different canister to bring it down to 34-36 total?

 

No, you need to bush the weights to limit mechanical advance.

In effect, you can limit the total vacuum advance by screwing it so tight that the diaphragm can't move the plate at maximum engine vacuum, but that's not the right way to control total advance.

 

So for right now, since low speed power is of main concern to me, I need to make sure the 10* is correct, and then work on the total of 32-36 mechanical with the vacuum unhooked.