So I rebuilt the 2GC with a walker kit and installed it onto the vista cruiser today but could not get the rpm under load to go low enough according to specs. With the choke fast idle cam OFF, the slow idle solenoid disengaged and the idle speed screw on the throttle backed off the lowest I can attain is 800 rpm in park, about 750 in gear. The carb was really coked up badly, the manifold vacuum port in the back for the PCV valve was clogged, the idle mixture screws were backed out to compensate for the ports being dirty, the choke plate would not open fully, the carb was a mess and the car was really gassy smelly all the time. So now that is fixed and I am glad but am stymied by this idle setting. Should I worry about it too much? Any ideas or suggestions are welcomed. On a side note, when attempting to set the timing I found the timing marker to be about 120 degrees retarded, I know the engine can't run like that and it sounds pretty good so I think the rubber may have aged the the ring has slipped some, read about that with Oldsmobile engines before. Anyway, thanks for the help.

 

Was the idle speed ok before the carb rebuild? What happens if the vacuum advance is disconnected and the hose is blocked?

Knowing that the ignition timing is probably not set to spec I'd be looking at that first.

Good luck!

 

I didn't even bother to check the idle speed previously because the the carb was in such poor shape but it did idle lower in the extremely rich condition that it was. I did have the vacuum advance disconnected, that is were I hooked up my vacuum gauge to set the idle mixture screws, the hose to the distributor came off and the hose to the vacuum gauge went on. And since the outer ring on the harmonic balancer is slipped (I think) I can't set the timing accurately. Maybe I could find TDC statically and then mark the ring anew. That might work.

 

If unable to adjust the carburetor idle speed to specifications then revisit: idle compensator; idle mixture needles (bent or scored if you reused them by chance); throttle valves could be sticking. Also the mixture needles should be adjusted evenly.

Hope this helps....

 

Vacuum leak?

 

Given the age and condition of the carb, my approach would be to clean a few other things up to gain confidence in your repairs. Since the damper is questionable, I'd definitely remove it and have it rebuilt. Damper Dudes in California is a place I can highly recommend for that. That'll give you confidence in your timing (assuming your distributor is in good shape). Once you have the damper off, you might want to consider replacing the water pump and timing chain while you're that far in there. If the chain has never been replaced, that's something you should really consider.
If you replace your water pump, throw a new thermostat in it - and new hoses. With your timing issue resolved, you'll be able to set your mixture and idle speed. The 2GC carb is stupid simple and will perform well once everything is working together.

 

Try to close the throttle linkage on the carburetor by hand. Will the idle speed drop?

 

Thanks for the recommendations guys. I was pretty thorough during the carb rebuild, spent 2 days doing it and evaluated all the rods, bushings, surfaces etc. and have a good measure of confidence in their condition. I am sure that the throttle valves are not sticking. The idle mixture screws are not dead-on straight and wobble a little when rotated but the tips are smooth and unblemished. I set them statically at 2 turns out which was too rich of course. As soon as the engine was initially started after putting the carb back on the first time I turned both of them in a quarter turn right away. Later when setting the vacuum I turned them both in some more, maybe a full turn but I can't guarantee they are both exactly even. There could be a vacuum leak as I didn't replace all the hoses and lines, that is a possibility. Confidence in the general condition of the rest of the engine is a point, maybe I should share some history of the vehicle. I bought it from a single lady who had kept it after a divorce a few years ago. Her and her ex were the third owners and when they bought it in '98 he started fixing it up and maintaining it, I think he even took it to shows because there was a sign like the kind some people put in front of their cars when they show them that was in the back with a few extra parts and loose trim. I was able to speak with him and he reported to me the things he had done to it over the years up to their divorce when she had it alone. He had boxed the rear control arms, installed a 1 inch anti-sway bar in the rear, installed a 1 1/2" anti-sway bar in the front, replaced the front and rear shocks, rebuilt the front and rear brakes, installed an HEI distributor, installed a replacement aluminum radiator, installed a set of headers with new pipes all the way back, had the a/c recharged, replaced various maintenance items over time like belts, hoses, etc. I got the impression that he really tried to maintain the car and even go a little beyond that (the sign for instance) and he was proud of it and wanted to show it off to people. However, I don't think he was very familiar with Oldsmobiles in particular or an accomplished mechanic in general. As an example, when he installed the HEI distributor (or had it done) he just hammered on the lower rear edge of the air cleaner housing to gain clearance since the HEI is of course bigger than the stock points distributor for '72. So it was all mangled and wonky with the paint peeling off of it. I must admit when I first saw it I started to try to hammer/straighten it out myself before I realized why he had done that and stopped myself, I just thought he had dropped it threw it against a wall during some fit of anger, who knew? He had removed the heat riser pipe when he installed headers since there was no way to re-use the shield and riser after that but left the rest of the stuff in the air cleaner housing "snout". Personally, I would have found some better way to make clearance and I will do something about it, maybe cut out the area to make room and then weld in a new piece, then clean and sand everything down and re-paint it nice. I don't know yet. My point is that most of those things that he did tell me he was very conscientious about taking care of the car and was not afraid to spend money on it either but he may not have been familiar with Oldsmobiles and their quirks like the loose ring on the harmonic balancer. At any rate there are some more things I can look at definitely and it could be one tiny thing that will finally correct this issue but I am not sure how imperative it is to correct it or how much of a big thing it is really, I drove it last night and it runs great with no hesitation off idle, no stumble at mid-range or top end, it even barks the tires with little effort. A 350 2 barrel ! Over all I am happy with the carb rebuild just not sure about how close to tune-up specs we should stick. For instance, the specs on that engine call for 8 degrees initieal advance timing but many of the cars on this site are running 10 or 12. Doesn't seem to hurt them. Finally, (whew, sorry for the length of this post) The throttle linkage will not close any more when I push it by hand with it unloaded, the idle speed does not drop.

 

They don't need to be 'exactly' the same, in particular if they're not dead-on straight, they wobble slightly, etc., etc. What is important is they are each set to achieve the highest vacuum possible. Therefore, irrespective of where each idle (A/F) mixture screw is set, adjust each until each achieves the highest vacuum possible. Many can perform this by evaluating the RPM. The higher the RPM when evaluating/listening/measuring should equate to the highest vacuum possible (without stumbling). A vacuum gauge is the preferred method, but not the only method.

 

Yes, I used a vacuum gauge and achieved 19 inches of vacuum so I am pleased with that.

 

Oh heck yeah - great vacuum.

 

It sounds like it is running great. I usually run around 1000 rpm in park hot, which ends up around 750 to 800 rpm in gear. If there are no vacuum leaks and it is running great, a slightly higher will run just fine.

 

Make sure the throttle linkage is adjusted properly. I had to lengthen the adjustment on the throttle rod (From fire wall to carb) as it was keeping the throttle from fully closing.

 

Good thought and I have had that problem before on a car when I changed the intake and carburetor on a '71 Cutlass that I had. In this case when I closed the throttle linkage by hand per Dynoking's suggestion there was no resistance offered by the throttle cable, intermediate choke rod, accelerator rod or throttle plate/rod itself. Everything is smooth and works as advertised. Frankly, I must recommend that anyone who has carburetor trouble or tune up trouble and suspects the carburetor to rebuild it to specs using all the correct static shop manual pre-set measurements. I found the only thing that I had to adjust in any great amount was the idle mixture screws and the choke unloader rod a little bit. I really am happy with how the car idles and runs it was just that the idle speed would not drop down to what the specs said, otherwise I am way happy with the performance.