Thanks for your thoughts Jerry , TC.
The engine is 216 standard.
The heat tubes are 3/8" dia, the manifolds came threaded for the brass fittings I have used.
I will see if I can increase the size to 1/2"
Yes TC, I used a vac gauge to get max vacuum.
The only ID on the Zenith is 20 on the throttle housing.
I have always run the timing on the ball , but today I advanced it 2 deg on the octane selector (91 octane fuel) got another 1" on the vac gauge , it has improved a bit , but I think the heat makes more difference. I will try to find some 1/2" fittings and tube.
