Wow, this is a lot to think about. I'll try to figure out if the boost is running out or if there just isn't enough there to begin with. The extra canister seems like a good idea as it won't add any mechanicals, but it could be that there just isn't enough vacuum to begin with. I'm thinking I should try to hook a gauge into the line and see how much vacuum the engine is producing to begin with so I have a place to start. Any idea what a good number would be? It seems once I know that, I'd know which direction to go.

z boy, if you do decide to install a vacuum canister you don't have to spend $65 for one, I use a camping propane canister. Make sure it's empty first, the safety valve is just a schrader valve like from the valve stem on a car tire, unscrew it and blow some air into the canister blow out any remaining propane gas then drill out the main valve and the safety valve hole to 5/16", slip in a couple of pieces of 5/16ths hard gas line and solder, braze, weld or even seam seal them in.  If I remember right the brake booster requires less than 14lbs of vacuum to activate the diaphragm so not very much.

 I love it. It lacks duck tape but there's a bit of Red Green in that set-up

fwiw, vacuum is measured in inches and microns

12 minutes ago, sweatybetty said:

fwiw, vacuum is measured in inches and microns

Thanks sweaty, 14 inches of vacuum, does that sound right? I know the boosters are pretty efficient.

14 inches isn't bad... That's what SHE said!!! 

59 minutes ago, grannyknot said:

Thanks sweaty, 14 inches of vacuum, does that sound right? I know the boosters are pretty efficient.

iirc, on a normal, stock, fresh engine, vacuum should be a steady 21" +/- at idle

46 minutes ago, Chickenman said:

14 inches isn't bad... That's what SHE said!!! 

would be more like it

Wow--what a solution, Grannyknot, I'll definitely look into that once I find a way to measure the vacuum that's there. I'm thinking that at the high rpms of the track, the car is producing plenty of vacuum but maybe I'm just using it up. Seems like this would be an easy thing to test out to see if it helps as a next step. Also, I noticed your brake check valve is different than mine...mine is some plastic thing. I figure I'll replace that, too, as even if it's not original, the PO was working on the car for 16 years before I bought it (not running) and it's been 5 since then...so could be it's lost a little of its effectiveness, too.