Carburetor help needed

Sounds like you have a loose vacuum line or a hole in a vac. hose somewhere.

CJB wrote:

You may have a problem with the idle circuit itself. Some applications have solenoids that control the idle position of the throttle or the amount of air supplied to the intake, thereby controlling idle rpm. It could also be the idle jets are clogged or the idle air bleeds are clogged.

A carburetor has different fuel feed paths that become active at different operating conditions. One circuit to supply fuel at idle, another that provides additional fuel during the transition from idle to cruise, the main metering circuit for normal cruise RMP, and one or more power circuits for hard acceleration or increased power. Only the idle circuit is active at curb idle. The other circuits start feeding fuel as the throttle plate is opened further. At cruise the idle circuit is still feeding a small portion of the total fuel charge. If the idle circuit is restricted, it is not very evident at cruise because the other circuits are feeding the majority of the fuel.

Hope this helps.

Ammonman

That does help. This carb does indeed have a stepper motor that controls the idle speed. The motor is working, but unfortunately, the motor dies before it gets to a low enough speed for the motor to advance to control the idle. Does that make sense? If I were to guess, I'd say that the motor will run fine at 1200-1400 rpm, but dies below that. The curb idle on this truck is 700 to 800 rpm.

My previous carburetor experience is limited to small engines and a couple of 2bbl autolites on older F-150s. I'm not even sure that this carb has an idle air adjustment screw, but that's what it acts like to me.

Does anyone have additional suggestions?

CJB

I found a NEW carburetor on eBay for $150, half the cost of a reman. Installed it and the truck runs literally like new.

Thanks all,

CJB