Last night we put my neighbor's rebuilt Rochester carb back on his 73. In addition to the problem with the windshield washer problem posted earlier we ran into an idle adjustment problem. He purchased a correctly dated and rebuilt Q-jet for installation. We swapped in the "new" old carb and the engine fired right up. When I tried to lower the idle speed, I couldn't get it to go below 900 rpm, with the engine warm, choke off, and the idle adjustment screw backed all the way off. I don't know Q-jets at all, since I have a Holley on my 66. Is there something I am missing here? It seems as if the large cam on the left side of the carb, where the return spring and accelerator lingkage attach is at its forward most travel, yet the rpm is too high. What other adjustments are there to bring this idle speed back down? We even went so far as to completely loosen the throttle cable to make sure it wasn't holding the idle adjustment lever off of the stop. Then we pulled on the return spring to make sure that the idle stop was at its forward most position. Both did not affect the idle speed. Thanks, Gary
-
-
Re: 73 carb problem
Idle speed on a '73 is not controlled with the idle speed screw, surprisingly enough. You mentioned that the large cam on the left side of the carb is fully forward. It should be resting against a 'plunger' with a hex head, the plunger in turn sticking out of a solenoid with a single wire attached.
To adjust the idle speed, take an open end wrench and turn the hex head on the plunger. I think it's a 9/16" hex, and turning clockwise will reduce idle speed.
Hope this helps,
Mike
NCRS Quebec chapter -
Re: 73 carb problem
Gary, Mike's on target. I would get a 73 Chevrolet Service Manual to set it up right. There's more to it then the idle solenoid adjustment, that just sets the intial idle speed. To get it to 900 RPM (4spd L-82), you have to adjust the mixture screws. If it's the right motor, follow the Emissions Label for the entire proper procedure. TimComment
-
Re: 73 carb problem
Mike and Tim, I should have been a bit more thorough in my explanation. The carb does have the idle solenoid (he said this was an anti-dieseling solenoid) attached. He bought a complete setup, including that solenoid. In addition, he has the 73 Judging Manual, AIM, and Chevy service manual. What I was initally trying to do was get the idle down from 1100 rpm right after we finished the installation. The hex headed plunger is far enough forward that the the arm on the cam doesn't touch it. So, being the curious type, we just backed off the idle screw and then the cam came to rest in its full forward position, without touching the hex head of the idle solenoid, or the idle screw. It was still idling at around 900 rpm. I guess I will have to read up in his service manual.
It seemed intuitive that backing off the idle screw would lower the idle speed, just like a Holley.
Thanks for the information, GaryComment
-
-
Re: 73 carb problem
Last fall, when we tuned it up last, timing and all other engine parameters were fine. It is running rich though. We will get on that tonight.Comment
-
Emissions?
You aren't talking about what you've done per CSM tune up proceedures to divorce the effects of the emissions control system. Tune up proceedures tell you to start the car, let it warm up FULLY, let the choke & pull-off mechanisms disengage, then disconnect/plug distributor vacuum and take the 'appropriate' measures to de-couple the evaporative control system (steps vary with individual model years starting in '71 forward). THEN, you adjust the curb idle RPM and tweak the idle mixture (interactive), move on to setting nominal RPM for the choke assy to handle cold start conditions, and last adjust the TCS/CEC/anti-diesel solenoid.
If I read your initial post literally, you're trying to 'tweak' curb idle with a cold engine where the emissions control system is engaged, doing it's thing to boost RPM and compensate for initial cold startup conditions. Maybe I missed something and/or you didn't say everything....Comment
Comment