Please forgive my ignorance, this is the first carb. engine I have ever seriously worked on. anyhow I have A 4-bbl holley and I was wandering do the idle screws effect gas flow once you open the throttle? what I am trying to say is if I lean out the idle will this also lean out the mixture at mid and full throttle?

also is there an easy way to tell when my vac. secondarys are opening?

 

The Idle circuit really isn't in play after you open the throttle. I'd suggest maybe buying a book on rebuilding Holley carburators.

BBT

 

Dr Ford,
You should've paid attention for all those years in school, Doc. Holley Carbs are very simple to work on as long as you pull them apart every week. You can adjust the floats while the vehicle is running in about 60 seconds. You must remove the float bowls to replace your primary/secondary jets. If you have vacuum secondaries you should be able to pop your throttle manually and see your secondaries open. If they don't, you can change the spring in the round black plastic diaprham to get them to open sooner. A holley trick kit and a holley carb book will square you away. Start there.
Good luck, Have Fun,
KingFisher
P.S. If you get into this, investigate your "power valve", it's worth it. That's how holley delivers the serious fuel on the secondary side.

 

I have worked on Holley's for a long time and they are not that bad(easier than a quadrajet). Ok, from your post it sounds like you are running rich at some stage. The idle mixture screws only adjust your idle. Once you open the throttle up to around 1200 or so rpms the primaries come in.

There are a few things that can cause it to run too rich.

o The choke is staying closed or even partially closed all the time. Thats easy enough to visually check after you warm the motor up.

o The floats are riding too high. This will be seen as gas dripping from the front or back venturi's at idle.

o The power valve is blown. The only time the motor will run well is from around half throttle up. The rest of the time it will be way too rich and pump out black smoke like a chimney. If you've had any significant backfires through the carb its likely that the power valve has been stretched or blown.

o A badly clogged up air filter prevents the carb from getting good air flow. Thats a simple one.

o Somebody has monkeyed with the carb and jetted it way up and got it out of whack. Well that requires finding out what jets it has.

o Dirt and other crud is clogging up the high speed air bleeds. You need to take it all apart and clean it well to fix this one. In general, if the carb is really dirty it needs to be taken off and sprayed really well with carb cleaner.

On the secondaries you need to wrap a small wire around the vaccum linkage. This is the lever on the bottom of the secondary vacuum pod on the side of the carb. Pull the linkage up to make sure the wire is not too tight and will slide when it opens. Go out and test drive it. When it opens it will slide the wire down on the vacuum linkage and you can check it. Good luck.

 

Hey hottarod that is a pretty good idea on tying a string to the secondary lever. It is so simple that I didn't even think about it.
the carb is a holley 750.
it is on a 74' 330 FE.
I went the whole nine yards and rebuilt the carb.
for the most part the truck runs pretty good, exept for a few bugs.

could this carb be too big for my 330?
BTW the only reason that I have this big of a carb on this engine is because it was free A guy gave me the carb and a 4-bbl intake for free. all it cost me was $31.00 for a rebuild kit :-)
I figured that it couldn't be any worse than my 2-bbl Motorcraft(if it were a horse I'd have to shoot it)

any comments or tips?