Vacuum Leak on 360

[George G. Leverette]

Here is the setup Mopar 360 short block, Performer RPM heads and intake, Holley 750 carb. This is the problem; only 5" of vacuum at idle thecar starts immediately and idles, sluggish until about 35 MPH the smmots out. Tried the spray thingy around the carb and intakes with no change in RPM, also blocked all lines and ports with no change, can lay towel over carb throat without engine dying, I am annoyed at wits end, confused and begging for help, I wanna smell some rubber burning.

[ajmopar]

A few questions George:

1) Is any oil being burned? Just wondering if the intake is leaking from the gaskets into the valley.

2) Have you inspected the intake manifold for cracks?

3) Where do you have the initial timing set?

4) Is the valve lash/lifter preload set properly?

My inkling would be to pull the intake and inspect the gaskets carefully for signs of oil seepage and leaking, and inspect the manifold for cracks or poor machining. It is possible the deck height on the block is wrong or different side to side, making it very difficult to seal the intake, given what others have said about the crate motor bottom ends. Now that I think about it, I would try another carb first, just to rule it out.

[ohioDemon]

I think i would try someone another carb first.

try jetting your carb primaries up 2 jet sizes

[mtrv8n]

May also be the distributor. It could be sticking, not advancing untill spinning faster than 3000rpm. You'd have poor idle vac beause of no advance past initial, and so on..

[George G. Leverette]

This is a new engine combo, less than 100 miles on it. I appreciate the responses and will try each suggestion and reply here, later.