Well I installed a bigger cam in my 350 and after about 2 weeks the engine will smoke a whitish blue lingering haze only on start up after sitting 15/20 mins, that smells just like my 3$ a qt oil I just put in!
I figure the bigger cam moving the valves further open wore out the seals and /or guides.
So anyway I surfed for heads on Evil bay and determined what I was doing with the car and its purpose verses cost of heads.
The heads on it now are 624s with 194/150 valves, well on bay I spotted another set of 624s with 202/160s, pocket porting to unshroud the valves, screw in studs and guide plates, 525 springs, milled down a little bit from the factory 76cc.
So I bid and at the last minute got them for $406.
The car runs decent now so these heads should help somewhat and not for a smal fortune!
And one other thing, Im not too impressed with a quadrajet, runs OK but takes alot of gas pedal to get it going.
Im going to go with a 650 DP Holley and work my majic on it.
I think it will idel better and perform off the line better.
I just wanted to see if for the first time I could get a quad to perform with a performance cam?
Results: lackluster,did it work, yes.
So on a scale out of 1-10 I'll give it a 6.

 

The 624 heads are known to be prone to cracking around the exhaust valve seats given they are the lightest casting that GM produced for the L48/L82. I'd take a close look at the set you get just to be sure they are ok.

How is your ignition timing? Properly adjusted for performance (vs. emissions), you can gain considerable HP/torque that can be felt off the line. That may be the reason for the slow start off the line (too little ignition advance and perhaps not enough full advance until too high an RPM). If you had the time, I would recommend a "Lars" rebuild of your q-jet; that is, if he is rebuilding them now. He works wonders and you spend nearly half of what you would on a replacement Holley which will still require tuning.

On my '80 L48, I went with a recurve of my Accel Performance distributor by a tuner and picked up about 40hp/tq... that was, after I had sprung for the DART heads, Edelbrock performer intake, hypereutectic pistons, headers, duals.... you get the idea. Too little ignition advance can diminish the benefit of performance parts. I sprung for the Lars rebuild of my q-jet after the tuner took a grinder to the metering rods.

 

Don't give up on the Q-Jet just yet!!

I've done the same thing as you on my ZZ4 but with Brodix heads and a different cam. It's a bear to keep running when cold and it stinks of gas like it's running rich. The problem is that the idle circuit is running lean and has to be modified by opening up the idle restriction slightly. I went from 74 jets to 76's and saw an improvement in how the car runs but it didn't completely solve the performance. Make sure your ignition curve is properly dialed in as someone else said and if so look at modifiying the carb to better match the needs of your new motor.

I'll post a link to a good article that explains the procedures on opening up the idle circuit when I get home.

 

Im at 36 at 2500, and 23 at idle. #77 jets.
like I said, it works and runs OK, but I am more a holley man for the last 25 years working on cars.
Thats a very wierd thing, you run a quad on a vette with a 350, but the same 350 in a Camaro and it has to be a Holley?
Anyway I just wanted to see how it was and I got it to run decent.
The heads have been magnafluxed and are fine.
I don't think i'll ever hurt them.

 

I won't argue about using a Holley if that's what you want, but, like what was said above, Lars can make a Qjet work to perfection. He did one that I have and another local "expert" did my other Qjet. There is no comparison. Lars is the man.
Also, what torque converter are you using? Don't minimize its impact on off-the-line acceleration.

 

Here's the link to an article about performance modifications
http://www.highperformancepontiac.co...buretor_tuning

 

I think alot of times peoples's quadrajets are running so badly that one out of the junkyard would be an improvement!
I don't think theres much performance you can add to a quad other than tweaking or adjusting it to the specs.
So when they send one off and get it $$$ rebuilt it comes back running the way it should and that IS an improvment over what they had, theres not much you can do with primaries less than an inch in size, theres only so much air going to go down them.
I have had Hollies for 25 years from the junk spreadbore to the 850DP and the best ones are the simple 600 vacuum and the 750 vacuum, they can be made to work on anything!

 

Years ago, I had a Qj on a 455 Poncho engine that ran like crap, sent it off for a rebuild, came back perfect, I called and asked what he did....he said the problem was in the 'off idle transferr circuit' it has to do with those two tiney squared off slots on leading edge of the primary throttle blades....they allow extra gas into the engine, and are set very lean on emissions cars, so taking a Qj from '68 up and expecting hotrod performance is not going to happen.....now the fix is there are 4 brass tubes in the top plate, I forget which two it is, but examine the structure and you find two of them go to those slots....the tubes need drilled out a slight bit, VERY slight....note the number bit size there to slip fit now, and redrill for next size up....try it, go from there.....

the guy's name was Brad Urban, Ontario Carb shop....California....

he died years ago, I understand...