LeakJune 19 2017 at 6:23 AM
Falcon67 (Login Falcon67)
Response to New build, Holley problems
Not sure what you tightened, but there a 4 bowl screws not two. A 750 VS has a metering block in the rear and there is a single gasket that seals the block and the bowl to the main body. You can tighten up the rear bowl screws - 4 and see if that stops it. If you have need to change the gasket, you'll need a clutch head screwdriver of the correct size to remove the metering block. I would also check the base plate screws.
After you get it to run dry, remove the float level site plugs on the side of the bowls, one end at a time - with the engine running - and adjust the flat level so fuel just touches the lower threads of the plug holes. You need a screwdriver and a 5/8" wrench. Turn the nut left to lower the fuel level, right to raise - little bit, like 1/16 turn - goes a long way so go slow and let the fuel level settle at the new setting before changing it again. Note that you have to loosen the lock screw just a bit, which will leak fuel from under the screw head.
Idle - start with the screws out about 1 1/2 turns unless its a 4 corner unit, then maybe 1 turn out on each. Turn in until the idle starts to drop, then back off about 1/8~1/4 turn. You'll go around a few times to get them all about the same, usually in the 3/4~1 out range.
Power Valve - If it's any kind of a newer model, there will be a check valve in the baseplate to protect against a backfire. I have been running Holleys for 45 years and I can say that I have changed power valves for age, rating, gasket replacement, etc but I have never actually seen or handles a "blown" valve. Typically they might have backed off or the gasket leaks. A lot of "blown power valve" issues - IMHO - are actually leaking main body gaskets, letting fuel into the wrong passages.