corvette_maniac

This appears to be the wrong carb for my `75…. seems to be an `80? I've rebuilt it before … but the idle has really never been right. I seem to recall the previous owner mentioning something about doing something with the q-jet (bubba alert.)

My question is should I get back in there and see what jets/rods and make this one work or find a 70452* q-jet that would be correct? I read that the `80s q-jets were more on the lean side for emissions; everything but idle is OK. If I start with the idle mixture screw at 2.5 turns out, it won't even crank. I'm probably 6 turns out …. so I know it's lean.

jnb5101

If the case has not been distorted by over torquing the front mounting bolts, disassemble and inspect the carb. Read Lars' qjet papers and get Cliff Ruggles' book BEFORE you work on it. There's no way of knowing what's wrong until you open it up. The chance of finding a better (not Bubba'd ) carb is slim.

REELAV8R

I believe it was in 79 that the idle screws went to a finer thread. So a pre 79 carb that is 2.5 turns out May be the same as a 79 or later carb that is 6 or 7 turns out.
I would recommend Cliff's book as well. learning how the idle tubes, down channel restrictions and bypass air interact to produce proper mixture for idle is critical to idle and off idle performance.

Shark Racer

How much fuel is delivered via the idle mixture screw channel is determined by a few things:
1. Idle down channel restriction (the slightly recessed brass plugs on the sides of the float bowl wells). Bigger = more fuel
2. Idle fuel tube restriction (not visible from the top, but the brass caps that are flush with the top of the main body are the retaining collars for these, the actual restriction is about 1.5" below the surface of the main body). Bigger = more fuel
3. The size of the idle mixture screw channels (past the thread). This determines how responsive the mixture screws are, so you ultimately end up less turns out. Bigger = more fuel.

Now that I've said all that, if your carb is working correctly you should be able to get it to run well with the stock calibration assuming a stock motor underneath. 6 turns out is not a big deal if that's where it wants to be.

If you're running a 1975 L-48, that 80 Carb # should be just fine on your car.

corvette_maniac

Good word all .... Thanks. I did order Cliff's book as well. I have been wanting it for a while. I am going to tear down the q-jet. I'm also really curious to see what rod / jet combo is in there. When I bought the car several years ago, I recall getting the hunch that the fellow that I bought it from had been monkeying around in that q-jet. Just had that feeling ... might be something to it.

All other range besides idle is fine....off idle, part throttle, wot ....etc.

Shark Racer

If you feel good everywhere else, just open the throttle screws up a little bit more to smooth out the idle.

I'm assuming you've verified no vac leaks and all, right?