I currently have a quadrajet 4 barrel on my 305 Iroc Z. I am thinking of switching to a 650 Holly. Can someone help with which Holly would be a good replacement for the quadrajet so everything lines up good?

 

Your 1986 LG4 engine came with CCC Computer Command Control.

Your car has/had a computer controlled Quadrajet and a computer controlled large cap HEI distributor.

Does it still have those or have you swapped them out for a non-computer controlled Quadrajet and large cap HEI distributor?

 

The Holley spreadbore with vacuum secondary & electric choke. I don't remember the part number but you can find it on their website.
You're looking at $800 to $1000 with the price of the carb plus all the accessories to go with it. It's a good carb, but gets worse mpg than the Q-jet. And as mentioned, it won't work with the ECM...

 

Yeah, unless there is something wrong with the Q-Jet, I'm not sure that switching to a Holley is money wisely $pent. The only benefit that I can think of after money/effort is better throttle response due to larger primaries -the same feature that can hurt fuel economy.

 

What is wrong with the Q-jet? They're a fine, very tunable, carburetor. There are a couple of known issues that can pop up over years of use, but those issues are relatively-easily fixed. A new Holley isn't going to magically add 200 HP to the engine. :-)

 

Thank you guys for the responses. I just replaced my cam with a larger one and now the car acts likes its overloading. It's a manual car so it I shift in high rpms then it runs ok, but at low rpms shifting is studders. If I'm in 4th and go to pass a car it acts like its loading up. I have never been good at adjusting the carb as this is my first carb car. Any tips on adjusting it would be awesome and I could save money on not buying a holly. Also, it is still hooked up to the CCC. Ran fine until the cam swap. I'm thinking I just don't know how to correctly adjust it.

 

To ME, it sounds like something else is wrong, than the carb. I put a cam in an LG4 car....decades ago and it ran great w/o touching anything on the carb. Dropped a full second off my 1/4 mile time, even!

But anyway, if you want to diag the carb, run it for about 1 minute, at the throttle position where is is "overloaded" (not sure what that means), then, (in a safe manner) cut the ignition, pull to the side of the road, pull several or all of the spark plugs and take pics of them, post them here.

Or buy and install a WBO2 sensor.

 

how much more cam?
also, the biggest problems with the Q jet is the primary throttle shaft wearing out the alum base plate and creating vacuum leaks and tuning woes. wiggle the throttle lever with the return springs off, see how much it moves around.
there is a bushing repair to fix it.

 

As others have noted, you may have other issues than carburetor. What color are the spark plugs? I ask, because this can help diagnose whether or not you're running too rich or too lean.

What are the cam specs? If you're running a really big cam, you may not be pulling enough manifold vacuum to properly-position the primary rod hanger.

 

If you still have the factory carb and it still computer controlled does the check engine light work? Does it come on while driving? Are there any codes stored? Does the solenoid in the carburetor work?

 

I think the OP has checked out.