Ok so here's the situation, I had a holley 750 vac. secondaries rebuilt and I put it on my blazer with a 383 stroker. Started having problems fouling out plugs and thought maybe the carb was too big. Ended up having spring loaded needles and seats installed on the same carb (maybe offroading was causing the needles to hop thus allowing in more fuel). A few days later the plugs began to foul ONCE AGAIN but I was able to clear it out and save them for the drive home. Some people suggesting I may have problems with the heads due to the fact it had been sitting for awhile prior to me owning it. Any ideas as to what would be causing this?

 

Carbon fouling or oil fouling? What do the plugs look like when they are fouled out?

A 750 should not be too big for a 383 motor, especially with vacuum secondaries as the secondaries only come in as vacuum allows.

What are you running for main and secondary jets in the carb? Power valve? You may just have too much fuel going to the engine.

 

Well the plugs are all black when I last pulled out the old ones but only the driver side plugs were very bad the passenger side still looked usable (still were replaced). I'm not sure on the jet sizes or power valve I'm sure it's whatever came factory on the carb.

 

You really have to setup the carb to the motor. If that carb was last used on a big block motor, it is likely running way too rich.

I would pull the carb and remove the fuel bowls. Have a look at the jet sizes on each side. You can download the tech sheet for your particular carb model from Holley.com. You want to verify the proper components (jets, power valve, springs, etc) are in the carb before trying to tune it.

CLICK HERE for a pretty good tech tips paper on tuning a holley carb. You will definitely want to have a jet kit and a few power valves and springs for the vacuum secondaries on hand to get it tuned properly.

 

Well I went down and talked to a guy that owns a performance shop and he is saying it's most likely not the carb due to the fact it was just returned from the shop maybe 4 days ago and because my intake is a dual plane intake so it wouldn't be fouling just the 4 driverside plugs it would have fouled 2 on each side. He had reasoning which made sense saying the angles of the heads and intake might be different so its not seating properly so it is probably sucking oil from below at higher rpm due to the higher vacuum. He suggested to do a vacuum test while its running which I think ill do.

 

Man, that is a bit out there... Good luck with that.