potterc32

iTrader: (1)

I am going to be rebuilding my quadrajet in the next week.

only things i have done to the engine, are open element air cleaner, and shorty headers/ypipe and exhaust. Nothing crazy, plan to do roller cam, and performer intake soon. But would like some advice on jetting my carb. Should I just leave it how it is and use new jets and rods/hangers? or should I modify?

Also any suggestions and tips on rebuild are welcome as well, first rebuild, so all suggestions welcome.

I know I will be re-pluggin holes on bottom to stop draining into intake. Any other modifications or tricks? Thanks!!

potterc32

iTrader: (1)

!

Ozz1967

iTrader: (4)

If you haven't made the motor bigger than the 305, you don't need to re-jet the carb, it's plenty big for the factory motor even with a better intake and exhaust. Just buy a rebuild kit and go through it.

potterc32

iTrader: (1)

I did put a 350 in it, the 290 hp engine identical to the one from jegs and such. Nothing radical. But if I don't need to rejet the carb, I won't. Is that the only reason I would need to get new jets? I can't imagine they would wear out.

Ozz1967

iTrader: (4)

The jets don't "Wear" out, they just get too small or too big. MWnova66 did what you did but wth a bigger motor and kept his factory Qjet. The biggest issues is vacuum to pull fuel at idle but if you're running a cam that gives good vacuum signal you should be fine, you'll just need to tune the carb for the larger motor. Set Idle bleed, use the IAC to dial in the dwell etc. You might need to reset your rich/lean stops to get the IAC to dial in if you can't get it. Other than that the Qjet is already a 750 CFM carb so it's plenty "big" to handle the motor you put in.

potterc32

iTrader: (1)

Awesome, I'll just rebuild/ reseal and call it good.

five7kid

iTrader: (14)

I put a ZZ4 clone under my '86 computer q-jet. I didn't change anything from what I had done for the 305 that it replaced, other than adjusting everything to factory specs. The ZZ4 is rated at 355 HP. I had headers, free-flowing exhaust, dual snorkel air cleaner (don't like open element air cleaners under our hoods).

However, I had redone the secondary rods & hanger on the 305. And, I live at high altitude, which would reduce fuel requirements. I didn't have any problems with it with the 350, but only had it at lower elevations a couple of times.

For what it's worth, the primary jets are actually more than just a calibrated hole. The mixture control solenoid uses cycle dwell time to adjust the mixture by moving the metering rods in and out of the primary jets. So, they could indeed "wear out" - but I've never heard of it happening.

Also for what it's worth, the factory used different primary jets for 350s in B-bodies with electronic q-jets, than what was in the 305s with electronic q-jets (I believe that was also true between the base LG4, and "high output" L69). I would say if you can get everything set to factory specs, and it runs fine when in open loop (before it gets warmed up), you don't have to worry about the primary jets.

On the other hand, more than likely your secondary rods and hanger weren't optimum for the 305, so they are probably going to be just as bad, or worse, with the 350.

86LG4Bird

iTrader: (1)

To echo five7's comments, I just put a ZZ4-cammed Vortec headed 350 under the CCC Quadrajet which formerly fed a stock LG4. Other than the DR rods and G hanger on the secondary side which the LG4 seemed to like, the carb is still bone stock and runs great at part and full throttle with the ZZ4/Vortec underneath it.
I have the idle mixture screws backed all the way out, attempting to richen the idle enough with the lower vacuum the ZZ4 cam is pulling. Idle is acceptable; however I have a bucking/lean issue when off the throttle gradually slowing or just barely feeding throttle when cruising under 40 mph with the TC locked.
I'm wondering if I should restrict the fresh air intake side of the PCV system to keep it from leaning the mixture too much under higher vacuum.

Ozz1967

iTrader: (4)

That sounds exactly like what mine did.

With my cam, I had a lower vacuum than stock, so the idle wasn't getting enough of a vaccum sense to pull fuel properly which causee me to have exactly what you're going through. Otherwise it ran fine.

I eventually sent my carb off to Cliff Ruggles and had it rebuilt and now I don't have any problems with it other than a little off-idle bog that I just cannot for the life of me figure out.

86LG4Bird

iTrader: (1)

Just reporting back on this. Still tweaking it and have made progress.
I've ended up with the idle bleed screw turned down probably 6 to 8 turns from its original position, and the lean bucking when coasting down with the TC locked is almost completely gone. I had always heard that the bleed adjustment is extremely sensitive; that's why it took me so long to try extreme adjustments on it. The top of the screw is now about 1/4" below the top of its "housing", whereas it was about flush before with the stock LG4.
However, now it seems the ECM is attempting to lean this "more correct" idle mixture, and there's a 1-2 second lean stumble when I lightly squeeze the throttle before the O2 sensor picks up the lean condition and re-commands the MCS to correct it.