help w/ timing and vacuum adavance questions

[68GEETEE]

help w/ timing and vacuum advance questions

Running a 302, 4spd, new 600cfm Holley mech secondaries, stock Autolite Distributor with points (yeah I know) and single vacuum advance.

The engine was pinging at highway speeds 70 mph, especially going uphill. Put a timing light on her today, and set the timing to 10 btdc, she was at 0 btdc because I didnt have a timing light at the time.

Ok, I checked the timing with the vacuum adavance disconnected and hose plugged. From 10btdc she advanced to about 28 btdc at wot. Then reconnected the vacuum advance and at wide open throttle she is waayyyyy past 40 btdc. I know this is too much. Thats why she was pingning. The question is how do I get her not to advance so much at wot?? I have heard you can shim the vacuum advance, is this true, and how do I do that?

She is also stumbling when I punch the throttle, did it yesterday at the old timing setting, and did it today at the 10btdc, is this because of the vacuum advance, or is that a carb problem? (the carb is brand new). Appreciate your help, thanks,

Dave

 

[jikelly]

Does the engine stumble with the vacuum advance disconnected?

 

[68GEETEE]

Yes.

But now its even worse. I just realized that my spark plug wires were connected to all the wrong terminals at the distributor. Thats why when I connected my light to #1, it didnt work. It worked on what I thought was #5. I just reconnected everything, and now she cranks but wont start.

It dawned on me that the engine must not have been at TDC when the distributor was installed. I got the #1 cylinder to TDC, then pulled the dist cap off, and the rotor was pointing to #8, not #1.

SO I took the distributor out, and the freaking oil pump shaft fell back inside, but went the wrong way and is now at the bottom of my oil pan.

Anyway, when I get this all back together, how do I adjust that darn vacuum advance??

Dave

 

[Ozsum67]

You can put heavier springs under the points plate, so that the timing won't advance too far.

 

[stangman67]

I dont know if the stock vacuum advance can is adjustable, but i put a crane adjustable unit in mine and it allows me to set the advance amount by turning an adjuster screw in the hose port with a allen wrench. I believe turning it clockwise makes it advance more and at a quicker rate.

 

[68GEETEE]

You can put heavier springs under the points plate, so that the timing won't advance too far.

The springs are for the centrifugal advance. Its when you have the vacuum connected that it overadvances. I read an article about shimming the stock advance, but the article did not go into detail on how to do this.

 

[pabear89]

There are 2 differant types of vac controls.
one has a screw on diaphram and the other is a straight bolt on type.

The screw on type can be shimmed by using small thin flat washers to make the spring pressure tighter to allow less advance.
Add to lessen the total advance, subtract to increase.

The adjustable type can be reset by using an allen wrench stuck in thru the vac hose port. and turning the screw inside.

Both are easiest set with a vac pump that has a guage to see when the plate moves and at what pressure.

you can also preset you total advance too.

PB

 

[Ronstang]

You can put heavier springs under the points plate, so that the timing won't advance too far.

Heavier srpings affect the rate (slow it down) at which the cenrifugal advance comes on but not the total centrifugal advance and since it is only 28 degrees total with just the centrifugal then he only needs the vacuum unit to add about 10 more degrees. Every vacuum advance I have ever had was adjustable using a very small allen wrench inserted in the vacuum port. Now, I'm not sure if a factory advance unit is adjustable but all the ones I ever bought at the parts store to replace worn out ones on my factory distributors were.