Here's the scenario:
'71 307, open plenum intake, Carter AFB Comp Series carb, HEI, headers, stock cam.
Pulls @ idle, i.e.,900 rpm, 15-16 in/hg, steady. With alittle adjusting of timing and mixture screws, they do have an effect, 17 in/hg. Problem is there are three dead cylinders, #2,4,&5. Temp gun shows 120-140*F, all others are 400-450*F.
Pull plugs, they are not black, brown in color, I changed them anyway. Timing light shows spark for every cylinder at its plug. Cylinder compression check shows 125-133# for all eight. Removed valve covers to witness all rockers going up & down.
If I bring rpm up to 3000-3500, then vacuum comes up to 20 in/hg and dead cylinders begin to fire and engine smooths out. Let it idle, 3 dead cylinders. Carb has been disassembled and cleaned, sprayed manifold & carb and found no vacuum leaks. Place hand over air horn, engine dies.
I believe carb may be too big, or engine needs a can of Engine Restore to produce more vacuum to have carb function properly.
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