i have a problem. i resently put a new engine in my '87 camaro. it was running fine (haven't driven it yet). then i let it sit for a day or two and it started to have an erratic misfire. it pops/backfires out the exhaust (straight headers). all the header tubes are hot.
i checked the spark plugs and wires, power to the coil, coil, module, cap, and rotor. the compression is good, 160 at the lowest and 175 at the highest. i have fuel to it and the carb was rebuilt (it did the misfire before it was rebuilt, that's why it was rebuilt).
some specs on my engine: 750 holley, comp cam hydraulic roller .600 lift with 314 duration and 252 at .050. dart pro 1 heads, 200cc runners, 64cc combustion, 2.02 and 1.60, with 1.52 roller rockers. block is 4.030, 3.75, 6in rods.
when i hooked the vacuum gauge up, it said 0 (at idle of 1100-1200 rpm's) but goes up to 15 when i rev it. i've notice air is being sucked in through the valve covers. if i seal the valve covers up and shoot a little air into them, it blows some out through the carb.
now, is this all because a vacuum leak on the bottom of the intake manifold?
any help will be appreciated.

 

Sounds like the way too much negative pressure inside the crankcase (relative to the pressure outside the crankcase). This could absolutely be cause by a large vacuum leak involving the intake manifold. Seal up the vacuum leak and see what happens.

I think you are accidentally checking the secondary vacuum instead of the manifold vacuum, pick a different vacuum source to check.

 

ok, i'll reseal it and see what happens. i hope that is the problem. and i'll pulg the vacuum gauge into the vacuum this time around.
thanks

 

Also check the plug wires - I had one that would pop itself off the plug, just enough to cause issue, but looking at it it looked fine - make sure all plug wires are securely snapped on the plugs and cap.

 

i've replaced the wires, but i could've not clipped one down all the way. #8 header tube isn't as hot as the others, that could be why. i'm going to recheck.