running rich, how do i lean a 2 jet??

[fast_dev]

carb was new when i bought the truck, its a 2 jet on a stock 283 but its too rich, black smoke. what should the settings be, or how do i lean it out??? which screws are mixture??? Thanks, Devin

[Fast68Chevy]

the screws with the springs down on the base of the carb on each side(front) for each bbl are the misxture ones, i bet you you have more of a problem than just screw mixture setting, either have stuck float or bad needle and seat or dirt in it or choke stuck shut too far, try revving up engine pretty good and slapping choke shut to suck out any dirt and reopening choke just beofre engine dies to keep it going,

[fast_dev]

anyone know what the screws are supposed to be set at, are they both the same number of turns out?? which way is leaner, in??? Thanks, Devin

[Model 12]

According to my 72 service manual the 2bbl (2GV) mixture screws should be screwed in until they LIGHTLY contact the needle seat, then back them out four full turns.

At that time, adjust the carb speed screw to get to the initial curb idle speed, which is about 700-1000 rpm (depending on model).

Adjust screws equally in (leaner) to obtain final curb idle speed (about 600-900). Reconnect vacuum line to dist.

That skips a lot of adjustments, but that should get you going. I agree with Fast 68, plus if things are that bad, a carb zip kit may be in order, which will explain all the settings and give a choice opportunity to clean the carb fully with new float/needle seat.

Dave

[fast_dev]

thanks alot for the adjustment info, carb is only about a year old and has maybe 3000 miles since i bought it. it always ran rich since i got it, i never messed with it since i don't drive it regularly, when it was cold out it wasn't as bad as the mixture gets leaner in cold weather. now its a little too bad not to try to change it. Thanks again, Devin

[COBALT]

New meaning rebuild and/or reconditioned?

What happens when you go from idle to WOT? Does the engine stumble? If it was rebuilt it may have been rebuilt without adjusting the float level. Depending on your model the float level should have maximum rise and maximum sink within specific limits-hence the needle lets in the right amount of gas into the bowl. My 2GV had a hole in the float, so the carb constantly let in too much fuel into the bowl because it was sinking.

Also, check your accelerator linkage to make sure the pump is working right, and doesn't have play in the linkage (hence the idle to WOT test). A broken or in-play accel. pump will let in too much fuel when accelerating and it will stumble.

Adjusting the mixture needles is a bit of a pain, especially after a rebuild. I screwed mine in until they seated, then backed out 4 turns. Then I set the fast idle screw until the engine would hold idle at 800 rpm (for automatic transmissions). It ran too rich, so I backed out the mixture screws another 1/2 turn. You have to sort of guess as to what will be the best for you. It will change depending on bore size, and how the idle bleeds are configured. The bores on mine were smaller than some (like on a 327), but find where it runs too rich, and too lean, and split the difference. Finally, go back and readjust the fast idle screw until you hold the RPM setting (mine was 800) for your engine/transmission.

Other than that you'll be back to readjusting the linkages to the right settings...