hjgator

I have a 1979 corvette with ZZ4 in it it has a Q-jet it stumbles from a dead and then runs like a bat out of hell. My problem is I've had a 67 GTO and a 396SS El Camino with the same carb on them and hated that carb, had problems with all of them. Want to get a Holley dual feed , I have a friend with a ZZ4 in a 1977 with a Holley 750 cfm but he has an upgraded cam. Do you think mine will handle it. Thanks hjgator

Jud Chapin

It's tough to beat the Q-Jet. Contact Lars about rebuilding it.

StickShiftCorvette

I prefer Holleys. They tune relatively easily, and don't do the weird things Q-jets always seem to to do (drop floats, inlets corrode off, run like crap...)

A ZZ4 would work best with a 600 CFM, since it redlines at 5800 rpm.

rihwoods

Got the original Q-jet on my 78 L-82...no stumbling....works great...got a 750 Holley on the 69 502..same deal...works great...

Ganey

Holley 600 - 650 will work for you.

vettesbydesign

I was having problems w/the q-jet on my 75 L82,and HATE rebuilding them,so had a new 650 Edelbrock here.Not as responsive as the q-jet.Put on a Holley I had here.Same thing,so rebuilt the Q-jet.It is 10 times more responsive,than w/the Edelbrock,or the Holley.Now....if you find a spread bore Holley.....that would be the way to go!

American Boy

It's all about a question of taste. You could make all 4 barrel carburator to perform...as long as you tune them right.

For my part, I love my Q-jet because it fits well with what I do with the car. Because it's a spread bore, it has really good throttle response when on the 2 little barrels. That's what I like when doing street cruising and I get 20 MPG out of it on long highway run. Then when you floor it, it perform as good as any other when it's well set up.

So if you only want to put a carb that perform and be done with it without taking care of MPG, go with the Holley. Don't get me wrong, Holley can be made as an MPG carb but they need lots of tuning too. They are just simpler to make them run without big bug.

Since you already have the Q-jet, I would read the Q-Jet Tuning Paper and tune it.

Any carb need a lot of work to run flawlessly.

Stephan

Ganey

Actually an out of the box Holley 600 VS can get over 20 on the highway - as did the Q-J on the same car.

If one wants to use a squarebore carb out of the box size it correctly for the setup.

marshrat99

I've used QJets and Holleys with much success. Both are fine carbs. I'm currently running a Holley 670 SA and only had to up the jets per Lars. Unless you're really settled on a Holley, might want to try replacing your accelerated pump seals before spending a lot of more $$$ if just to get rid of the stumble.

hjgator

Thanks for all of the information, I think I'm going try changing the accelerator pump and tuning if that don't work then I go to plan B. Thanks for all your help.

RagTop69

Let me know how it works out. I have a 69 427/390 that is a relative slug too. I suspect that there are linkage issues with the Q-Jet that prvents the secondaries from opening completely, but can't find anyone to address it for me. I do know that I can't hear or feel the secondaries kick in. With the size of those suckers, you'd think it would be obvious when they began dumping fuel. My car is also M21 equipped. The "69 Corvette Fact Book" that I got from the P.O. with the car sites performance numbers from magazines of the day for many of the engine/transmission combinations and the L-36 with an M21 and 3.36 gears (exactly as my car is equipped) ran a 15.02 @ 92 mph back in the day. That isn't exactly stellar performance. Maybe we are both expecting too much from these old buses. I won't build the engine, however, for the sake of keeping the car stock.

BigBlockk

Make sure the choke is adjusted properly. If it isn't it can be engaging the secondary lock out lever, holding the secondaries closed.

BigBlockk

Later.....