[lucky1]

I want to reduce the amount of vacuum advance by a few degrees.

I’m not aware of any adjustable vacuum advance available for this distributor.

Is there anything else I could do to possibly reduce the vacuum signal to the existing unit ? Possibly the size or length of hose ?

The vacuum source is ported.

Thank you.

[Ozzmann]

Just make a stopper for the can you have, I have the same distributor and limited mine to 10 degree vac advance. If you do a search, there are threads on how to do it, I just used a small piece of metal and a screw.

[Brentco]

The ACCEL adjustable vacuum can for GM points fits the RTR distributor. Part no. 31034. The chart they give you showing turns of adjustment screw vs degrees of advance isn’t very accurate, so you’ll have to test yourself.

[lucky1]

Originally Posted by Brentco

The ACCEL adjustable vacuum can for GM points fits the RTR distributor. Part no. 31034. The chart they give you showing turns of adjustment screw vs degrees of advance isn’t very accurate, so you’ll have to test yourself.

Thank you!

[lucky1]

Thanks all.

[Brentco]

A few more notes about the ACCEL vac can. The can may rattle when you shake it (really sounds like something’s broken inside), but that’s normal and nothing to be concerned about. I’ve had two of these cans and both made the same rattling sound but performed completely fine.

The instructions say to start at full CCW, but sometimes the adjustment screw doesn’t have a stop at full CCW, and if you’re not careful the screw can lose its engagement inside the can, leaving you SOL. So if you want a reference point, I’d recommend starting by turning the screw fully in, CW, while counting the turns, and then backing it out that same number of turns.

The initial set up is just a rough guess anyway, since the chart they give you isn’t very accurate. If I remember correctly, it gave me more advance per turn then the chart would indicate. Although the numbers aren’t accurate the relationship is — so if you screw in the adjuster you get more advance and it starts at a little lower vacuum number.

I adjusted it for 10 deg of advance with it all in by about 11-12 inHg, and I believe that ended up roughly 2 turns in from full CCW. I’d recommend testing the can before installing it. You can hook up a vacuum gauge to the can and test what vacuum level the advance starts and stops (at that particular screw adjustment). Then after install test the amount of advance it gives you on the car, and make adjustments from there. You generally want in the neighborhood of 10 degrees vac advance and you want it all in at least 2+ inches below your idle vacuum, if you’re on manifold. I wouldn’t follow their method re: increasing the advance until you get a surge at cruise. Maybe that works for some people.

Installing the vac can is kind of a bear, and you definitely want to pull the distributor to do it. I avoid pulling the distributor at all costs, but it’s necessary here. Follow the part of the MSD instructions that show you how to take apart the distributor to lock out advance. You have to remove a C clip to lift the rotor and get the vac can in, and it needs to sit completely flat when you reassemble. You might also want to check the clearance between the rotor and the magnetic pickup while you have the distributor apart. From the factory mine was too close and actually rubbing, which is no bueno.

I ended up reinstalling my distributor rotated one terminal over from where I had it (and moving the plug wires over one terminal to keep timing the same), so the vac can points more toward the driver’s seat and there is more room for the vac line and adjustment screw.