Adjustable vacuum advance on on HEI

Ok, I just installed an adjustable vacuum advance on my GM HEI distributor. I can't seem to get it below 45 degrees at 3000 rpm. Backed out the adjustment screw to what I think is all the way out, still 45 degrees at 3000 rpm. All this is in the driveway with no load. Am I missing something? Mechanical is about 25 dgrees with th vacuum disconnected, initial is set at about 12 degrees. TIA

 

Did you try adjusting it in? Been a while but maybe it tightens the spring inside making it harder to advance the timing

 

I did. In felt like it loosened the spring. Spring felt lighterr all the way in.

 

How old is the distributor and what kind of shape the mechanical advance in, any wear the centrifugal weight pivots?

 

Distributor is mechanically solid. I got it from a guy in california. Probly came out of a mid 70's buick I'm guessing. Its an oddfire distributor. With the vacuum advance DC'd it on 25 degrees solid. I've been running w\o the vacuum advance for a while but decided to put in an adjustable one to try and improve my MPG's. I just tried it again, all the way in or out it still goes straight to 45 degrees over 1000 rpm's with the vacuum hooked up

 

Do you have it hooked to ported or manifold vacuum? Should be ported vacuum.

 

This is where I'm not sure. I've got it hooked up to the connection just above the throttle plate on the front left corner of the carburator. It's a Roch 2G.

 

I just read this.

You'll need to get an adjustable vacuum advance diaphragm from your parts store. It will run you about $20 or so, but it's well worth it. Parts stores will probably have to order it, speed shops will probably have it in stock. Make sure it's for a GM HEI.

Before installing it, check the instructions to make sure, but all I've seen needs to have the Allen adjustment screw turned all the way counter clockwise to DECREASE sensitivity. You do not want it to work fast, you want it at the least sensitive position.

Install it carefully as per instructions. If you have trouble reaching the mounting screws apply a little vacuum to the diaphragm, it turns the plate out of the way.

Install the limiter cam the new adjustable diaphragm came with. Set it so it only travels about 1/2 the way it did without it. You can make marks on the distributor body before and after the cam is installed to see where to set it. 1/2 way should give you about 14 degrees vacuum advance. Without that limiter it will be worse than it was with the original advance diaphragm.

 

Let us know how it works out for you. I just installed an HEI dist. and may hav to get an adjustable vac. advance too.

 

Well, from the reading I did, there are several different adjustable advances for a GM. Distributor. I saw a few with limiter plates. The one I got from oreilly's didn't come with one. I made a small aluminum block and screwes it down to the mounting bracket to cut the travel in half on the advance. It now stops at 35 degress.