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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
Folks, I have a 1986 IROC, 305 4bbl Rochester carburetor (Canadian), original carb part / production # 1708652.
I purchased a rebuilt carb and it's about 99% accurate to the original however, the new rebuilt carb comes with a an electrical connection (see photo) that I don't have on my original.
I'd be grateful to get insight into this connection, what it does and if anyone feels that I could go ahead and install it, or if ignoring this connection, will cause me more heartache.
Thank you in advance for your consideration.
Michael New / rebuilt carb with unknown connection New / rebuilt carb with unknown connection Existing carb, no similar connection Existing carb, no similar connection
Your original is model M4ME. It is not computer controlled. At the time, Canada's emissions regulations were less strict than the US, so cars going there got the old 70s type of that stuff. The replacement one IS computer-controlled, model E4ME. Without the computer to control it, it's impossible for it to ever work right.
The part you have circled is the throttle position sensor. Note also the blue connector at the pass side front corner, that your original didn't have; that's for the mixture control solenoid. The computer ingests various inputs (things such as throttle position i.e. driver demand, vacuum i.e. engine load, RPM, and engine & ambient temp) and changes the mixture, and the ignition timing, according to tables programmed into it. The computer operates the MCS by pulsing it about 10 times a second: the solenoid draws the metering rods down into the jets to lean the mixture, and a spring returns them to richen it. It also controls the idle air bleed at the same time: the idle system gets more air and less fuel when the rods are in the lean state. The % of the time that the solenoid is operated determines the mixture. Without that, the carb goes full rich all the time.
Obviously the distributor that goes with the computer-controlled system would have to be different as well. You OTOH should have the non-computer version, with a vacuum diaphragm sticking out of the pass side of it at the base. The older style dist like yours controls the timing mechanically.
Send it back and have them provide the right carb.
