I was attempting to set the timing on the 350 I have in my '85, and when I disconnected the vacuum advance, there was no change in the timing (as measured at the crank).

I was attempting to set the timing somewhere near 10*, but I was never able to come even close. I retarded the timing until it got to maybe 20*, and the car stalled. Right now the car is set at >30*, but I can tell for sure, as the line disappears behind the water pump.

I have the vacuum advance from the distributor connected directly to the base of the carb.

I am thinking that I either spun the outer hub of the dampner, or the vac advance on the distributor is busted somehow. The car seems to run fine, but I'm a little worried that something is messed up in there.

 

The lines on the dampner are known to be wrong but only by a couple * but not that much.

I would say your timing light is messed or you have the connector on the spark plug wire the wrong direction or on the wrong plug. The engine should still run right up to and maybe a bit past TDC.

 

Sounds to me like you have a stock balancer that's supposed to use the 12:30 timing mark, and you have an aftermarket or replacement timing cover with the 1:30 timing mark.

Personally, I'd put the light back on the shelf and forget about it; and set the timing to where the car runs the best.

Maybe, after you get it running the best, you could get your light back out and find a stain or scratch or something on the balancer with it, and install a homemade timing mark on the balancer right there, so you can quickly and easily put it back where it belongs whenever you get a wild hair and decide to mess with it.

 

Or you could do it the right way with a positive piston stop and figure out where TDC is and mark that....

 

how does one go about doing this? this also doesnt explain why my vacuum advance doesnt advance under vacuum. or perhaps its running at full advance all the time?

since high vacuum at idle = less advance, and low vacuum at WOT = more advance, shouldn't the springs be holding it at 20-something degrees advance if its somehow not getting vacuum?

 

ok firstly if you have the vacuum advance connected directly to manifold pressure it should give you more advance with more vacuum. Meaning that idle will have more advance and cruising and WOT will have less. but if you disconnect it and the timing doesnt change then its broken or the port you are connecting to on the carb is not ported to manifold vacuum.

The mechanical advance works off engine speed -- more rpm's mean more advance. One thing to remember when setting base timing is that if your engine is cold it will be much more difficult to get the engine to idle with low timing advance. First make sure t he engine is warm.

The positive piston stop is a tool that has threads on it that allow it to screw into the no 1 spark plug hole.

http://store.summitracing.com/partde...=KeywordSearch

Once you do this you can rotate the engine over till the piston hits this thing you have now screwwed into the spark plug hole. you mark this engine position on the balancer. Then you rotate the engine the other way until the piston goes down then up and hits the tool again. you then mark this position on the balancer and measure halfway between your two marks. this halfway point should be where the origional timing mark on the balancer should be.

If not then the balancer is broken and you need a new one. Of course this could also mean that the mark you are using to line it up (the 0 degree part of the tab on the timing cover) is in the wrong place. Either way you need to make sure you have a solid balancer (doesnt slip) and then make sure that the 0 degree advance part of the pointer is over the timing mark on the balancer when the no 1 piston is at top dead center by the method above.

 

Or, of course, there's always the common-sense option of "doing it right" {{GASP}} rather than rigging something to get around a parts mismatch. You know, the old "fence at the top of the cliff instead of an ambualnce at the bottom" mentality.

You could just go get the right timing cover to match your 12:00 balancer.

Your vacuum advance is connected to "ported" vacuum. There is no vacuum there at idle; only when the throttle is open far enough to cruise down the road. With a typical stock or near-stock distributor, expect to see around 12-15 degrees of vacuum advance, once the throttle is open far enough to expose the "port" in the throttle bore to mainfold vacuum instead of atmosphere above the blades.

See this thread for how vacuum advance works. Ignore the arguing and ignorance as best you can. https://www.thirdgen.org/techbb2/sho...hreadid=325451

 

Yeah -- thats doing it right.

And what did I say that he should "rig together"? I dont think I said to buy or modify anything except for the piston stop.

Everything I said above applies if you have mismatched or matched parts. And if they are mismatched you will find out the piston stop way for sure as opposed to just going out and getting new parts with no knowlege of what you need...

 

I had to do that, until I realized the centrifugal advance was in pieces.

 

I did the positive piston stop thing, and it turns out the thing was about 4 degrees retarded. I set it at about 10* and now it runs 100% better. a little carb tuning, and i should be as close to perfect as i am capable of

 

Was the balancer off or the timing mark??

 

well, there were actually a myriad of things wrong. first thing, i had the vac advance on the distributor in the wrong port, making no advance at idle; the balancer appears to be one for a 12oclock timing marker rather than a 1:30 marker; and the carburator was disgustingly rich. runs like a dream now.