Had a new motor built, 500" 400 block, 10.8 compression, .629 lift, 263@.050, my Bulldog heads from old motor, MP M1 single plane, Holley HP 950, MSD Pro billet Dist and 6al and TTI step headers 2" - 2 1/8".

It runs but not well. We're pretty sure it's a vacuum leak at the intake. First we found one of the extra four carb mounting holes for AVS style carbs (I guess) was drilled all the through to the plenum. We fixed that but still seem to have a sizable vacuum leak.

We suspect the intake's not sealing to the heads well, looking at the gasket after pulling intake could see indents along top of gasket where manifold was sealed but nothing along the bottom. Used intake of course but it looked as if it was never on a motor before. Cylinders on even side seem to have the issue based on temps at header tubes. Odd side was showing ~200* (didn't run it long) even side (#2 specifically) ~85* We checked and we know we're getting spark btw...

Tried thicker gaskets and used a little sealer, better but still not right.

Looking for a way to track it down, other than spraying carb cleaner trick, we tried that and found nothing.

Might put old Performer RPM on tomorrow I think to see if it makes a difference but would like to try to get the M1 to work

Thanks