Fuel Mix Adjustment Screw Broken/Missing? - Stock Carb

DGonz

The engine has always run a bit rich since I got my '86 B2000 truck back in February. The smell is even more noticeable since I deleted the cats (though removing EGR and the stock air cleaner helped with the smell of exhaust in the cabin.)

Taking a look at what I think is where the fuel mix adjustment screw should be, I see a bubba'd piece with some broken Aluminum. No screw is visible, unless it's deep in there.

Is there any hope in being able to adjust the mix with this carb? I'm holding out on getting a Weber in favor of Holley Sniper EFI when Spring comes.

MazdaMitch

DGonz nothing wrong in that picture. The tamper proof pin is removed so that YOU CAN adjust it and its only one screw and I see it there, it's on the bottom, visible.

Malkovich

Does look missing from that pic angle. It normally is in the bottom of the two holes. Stock, there should be a pin locking it, but the pin seems to be removed.

You can use a mirror to try and look inside (it isn't THAT far inside). Or what happens if you put a screwdriver in there... catches on anything? But I believe this adjustment only affects the mixture at idle... is this what you're looking to do?

Malkovich

Also, how's your O2 sensor? Many of our trucks have fouled up/ bad O2 sensors due to running rich and issues with burning oil for so long. The stock ECU with the stock carb is a feedback design does trim the ratio. This should have more of an affect outside of engine idling.

If your O2 sensor is bad, you may know that it's not worth cleaning it out as it's very sensitive and solvent molecules are too large to do anything with the microscopic aspects of the sensor. General advice is to go OEM as aftermarket may not play correctly with ECUs. However, my Bosch seems to have solved my running rich issue just fine.

Malkovich

Oops, I didn't zoom in enough on the pic. Can see the idle mixture screw there now. Yep.

DGonz

Cool, thanks! I see now that there is a screw head in there. Shame it's just the idle mix adjuster, not the overall mix adjuster.

The O2 sensor looked pretty awful. I removed it from the old header and installed it into the new one after extending the wire to fit the new distance, but you're right that I don't think it's accomplishing anything for the feedback system. I tried to get a reading out of it on my voltmeter, but it barely registered anything. I'll buy and install a new one and see if that fixed anything.