[gennaro]

Hello all I have a 81 TA , which used to be a 301 turbo. I have now have installed a 69 400 with stock 6x heads , summit 2801 cam . dome pistons ,headers ,stock intake. Turbo 350 with 308 gears. Runs decent but i think it should be better . I have the original tubo carb on it. Question is , is this carb suitable for my set up and wondering what i can do to the carb to it make it perform better or shall i invest in a different carb altogether . Keeping in mind i cant really go to different manifold as i have a shaker .Thx in advance

[Tom Vaught]

Draw Thru carb is really not designed for the larger engine at all.

Any carb off of a Cadillac, Olds (large engine), Pontiac (large engine), or Buick (large engine) would be a better selection.

Even a Holley 650 cfm Spread Bore Carb would work better.

Tom V.

[Dragncar]

You can run a Tomahawk intake, Street Domimator intake, Northwind intake with shaker hoods. Even a RPM with some Butler air cleaner.
Your engine would run very well with a nice, simple 3310 Holley.
BTW, I have a couple 650 spread bore Holley carbs I would sell.

[81TTA]

Are you certain you're using the original 301T Qjet? The original carb for an 81 turbo would be computer controlled.

When you put in the 400, did you leave all the computer components (i.e. MAP sensor BARO sensor, electronic distributor, coolant sensor, oxygen sensor, wiring harnesses, etc) in place? If so, the computer would be controlling the carb and distributor timing based on 301T calibrations. If you aren't using the computer and the carb is original, it's running "full rich" all the time while the distributor is defaulting to one of two timing based on RPM. Either way, probably not optimal.

You mention the car "runs decent". I'm guessing you either did keep all the computer stuff OR your carb isn't really original to the 301T. If you have computer-controlled carb and distributor without the computer connected, I don't think it would run very well at all! Can you get the number from the side of the Qjet so we can verify?

[77 TRASHCAN]

X2
The 301 turbo carb is a huge problem, whether you have all/any of the computer garb hooked up.... or not. Look forward 76-up Quadrajet, examples that Tom mentioned.

[Formulas]

If I remember right from examining one of those 301 carbs a while back the secondary air valve has a quite limited opening which is a undesirable feature for a 400CID

[Kenth]

If a CCC Qjet not using the computer you can pull the mixture solenoid, jets and TPS.
Run straight on regular 2GC jets w/o primary rods, adjust the stop for airvalves for full flow and replace the secondary nozzles for undrilled ones.

But, of course, it would be easier to use a non-CCC Qjet.

[gennaro]

The number on the carb is 17081276 , lower #s are 3240 DPA. I've replaced the distributor with a regular HEI. All turbo plugs and sensors are disconnected.Come to think of it I was being overly generous with the statement that it runs decent. Its very inconsistent , had trouble with the secondaries opening up , had to have electric choke backed off all the way for them to work. Also backfiring after wide open throttle , and hard starts. I seem to recall after removing the carb inside intake was somewhat wet with gas.

[Tom Vaught]

So there you have it, find a nice factory 1976 Q-jet carb for a large engine and bolt it on and drive it away.
My choice would be the Q-Jet over the 650 Holley Spread Bore Carb as things would be simpler for you
to get a close calibration right from the start.

Tom V.

[steve25]

Your going to blow that new short block up with that back firing taking place at full throttle since that's a sign of the fuel mixture being very lean!

[81TTA]

I agree you'll want to replace your carb with a non-CCC version. If you can find a carb from an application closer to what was used on 400ci engines as Tom suggests, that should make tuning easier.

Makes sense you'd see and experience everything associated with an overly-rich AFR. Sounds like the choke is staying closed with the primary rods always running fully rich. From what you describe about the backfire happening "after" WOT, I'd guess you're only (maybe) running lean on the tip-out transition. The 301T carbs received (I think) the richest secondary rods of any production application to try to keep combustion temps down at WOT. While at WOT, you shouldn't be running lean assuming everything is behaving as described.

If you plan on keeping the electric choke, you'll probably want to verify it's getting power. The issue you describe with the secondaries not opening and backing off on the choke to let them open will remain with the replacement carb if the choke isn't getting power. Plus, you'll keep the issue of running richer than needed if the choke isn't opening completely.

[Grand73Am]

76-79 Pontiac Q-jet would be the ones to look for.