stvaughn

While trying to solve one problem (sticky throttle thread) I realized that I really did not know how my distributor was set up or what my vacuum was so I detoured a little and started checking. I found Lar's instructions for setting up timing and this is what I found.

With the motor (230hp/283 in a 1960) warmed up and idle at 730 vacuum was 18-19". I disconnected the vacuum and tried to find full mechanical advance. Somewhere past 4000 I decided it was time to follow Lar's instructions and remove advance springs. I removed the smaller one and it still took 4000 rev's to get to full advance so I put the smaller spring back on and removed the large one. Now full advance comes in around 2600 so I set timing to 36* @ 2600 rpm and then hooked up the vacuum. Full advance now stops at 58* which is too much according to Lar's and others. Vac canister is B1 and is adding 22* when only supposed to add 16*. What's going on here? I did drive it around a little and had no pinging even when I lugged it second and third (3.70 axle) and no chucking in high at 55 mph.

Idle advance with no vacuum is 7* and with vacuum is 28* at 730 rpm.

Should I be concerned with the 58*???

Never a dull moment in my garage!!

Steve

Frankie the Fink

58* is too high....small block Chevy's like between 48* and 52* and my '61 is at approx 52* but that's pushing it. HOWEVER, you DO know you can't really measure the advance added by a vacuum can while sitting in your garage ? Right ? Centrifugal weights are RPM-based while vacuum advance is load-based and you can't simulate the cruise load of your car sitting still. If you aren't getting pinging or "trailer-hitching" when cruising it should be OK.

You also shouldn't have to completely remove a spring to get your total advance "all in" before 3000 RPM. Lars will rebuild/setup your distributor for nice money but you will be off the road for a while...as he works on it.

plaidside

Since you have 16-18 Hg at idle you could change your vacuum advance chamber.
Use a B-22 one, NAPA VC1801 or Standard VC171 which are available.
This will give you 16 crank degrees of advance at 14-16 Hg and give you a total at cruise, 52 degrees.
I would install some lighter springs to bring the total timing all in between 2800 - 3000 RPM with vacuum advance disconnected.
Joe

stvaughn

Frankie, I know that 58* is too high but that is what it is reading in my shop so potentially it will get to 58* on the road. The reason it gets to 58* is because my B1 can is pulling in 22*. That seems to be my problem. Is there a way to limit the advance added by the vacuum canister? If not then I need to replace it and see what happens.

Plaidside, I have springs on order and I'll try a B22 and see what happens.

Thanks,
Steve

Frankie the Fink

Joe (plaidside) is a bright guy...I would get the new vacuum can per his advice before anything else. You can limit advance but its a game of trial and error and messing around with the slot in the distributor more than you probably want to...

stvaughn

B22 vac can on order. Can it be replaced without pulling the distributor?

LB66383

I recently had a similar problem. My new B28 canister was giving me 19* instead of 16*. Got it from Autozone, chalked it up to quality control of an offshore-made part. Anyway, I took it out, slipped a piece of tubing over the arm to limit how far it could be pulled into the slot, reinstalled it, and gave it the test. It moved my total vacuum advance back to 16*.

Yes you can remove/install a vacuum advance canister without removing the distributor. You need a Mityvac or some other way to apply vacuum to the canister so you can pivot the plate out of the way of the mounting screws. I always have a magnet at hand so nothing falls down inside.

Avispa

Frankie, I agree you can't measure the vacuum advance under part throttle load conditions in the garage....but you certainly CAN measure the maximum vacuum advance applied by the vacuum can as well as the centrifugal advance. The manifold vacuum will be at maximum at no load with the RPMs at the beginning of the power band of the cam.

Yes, 58 degrees may be high for total advance, but if the OP's engine is not surging or missing at part-throttle cruise, that amount of total advance will be ok.

Steve: If you don't want to change your factory or stock replacement vacuum can, Crane makes a kit that comes with a vacuum advance limiter. The limiter screws to the distributor body on top of one of the vacuum advance can mounting screws.

http://www.jegs.com/i/Crane-Cams/271...ductId=1581008

Frankie the Fink

Yeah, I said the same thing in post #2 early on.
I always just put an Acel adjustable vacuum advance (#31034) in my cars and tweak it how I want it.

stvaughn

I think the only reason my engine didn't surge at cruise is because I never got full mechanical advance in because the factory springs are to strong and the rev's too low to pull the weights out.

I went to my local speed shop and ordered a Mr. G spring set so I could get full mechanical advance in at 2500 and a VC 1801 can. Picked it up and what I received was an Accel 31034. Got on the forum to ask about the 31034 and guess what, FtF answered my question before I could ask. Tomorrow I put on new parts. I love my life!!

Spent three days putting in a slush box in a 74 'Vette. Out and in three times because nobody told us that an engine with a big cam doesn't work well with a street converter. Never too old to learn new stuff. Just don't have enough time left to learn all I want to learn.

You guys are a great help, thanks. Hope to meet some of you at Lakeland in January.

Steve

Frankie the Fink

Don't do the "happy dance" quite yet. Lars and others will tell you that some of those recurve kits (nearly all actually) don't use hardened parts like the original GM vintage stuff. Also the lighter spring selections can lose tension quickly and not allow the weights to fully return when no mechanical advance should be engaged:

http://www.arkansaspontiacs.org/tech...s/recurve.html

Don't know exactly what kit you bought but avoid using the weights (if they are included), stick with the GM originals, and try to stay with the heavy or medium spring set and recheck your advance curve after 500 miles or so.

stvaughn

Frankie, my wife says I have two left feet so no dancing for me anyway. Still waiting on a Mityvac to check the VAC but installed the two medium springs and got 36* at 26-2800 rpm. Is there a reason not to use two springs of the same size? The factory springs are not and Lar's recommend using two different size springs in one of his papers. Two the same size, good or bad?

Steve

Frankie the Fink

IIRC Lars recommends that as the disparity in the strength of the springs flattens the advance curve. If you get the curve where you are happy with it and the springs are the same I'd say leave it alone.