Most Corvair carburetors are getting a bit old - add to this the fact that many of them have sat around cow pastures for the past 10, 20, or even 30 years and you can have some real problems. (Make sure to read "The Final Word" below first!)
I HAVE A LACK OF POWER - This is especially common on cars that have been sitting around a long time. Old fuel may be the problem, but it is more likely to be brittle rubber internal parts that no longer function. The accelerator pump is the first culprit. A hardened needle (needle/seat) is a dangerous problem because there may essentially be no shut off for the gas. Any Corvair carb that has sat idle for more than two or three years should at least have an internal kit installed (Minor kit U-373). It's also very important to keep in mind that malfunctioning needles and seats can cause the carb to overflow - causing a very dangerous fire situation. When in doubt, never use old carbs as they are - even NOS or old "rebuilds".
THE CAR WON'T IDLE - A lot of things can cause this. First check and make sure that all the rubber hoses and connectors are sealed - what you are looking for is vacuum leaks which make proper adjustment of the idle impossible. The vacuum balance tube connectors, distributor vacuum advance hose and the choke hoses (62-69 only) are common leak spots.
Next check the carburetor throttle shafts - if they are badly worn, they will act the same as a vacuum leak. For moderately worn shafts install our throttle shaft seal kits (PN U-1608) - for badly worn shafts you will need to install new throttle shafts - our repros are U-1355 (60-69 non-turbos only). In addition, if you replace the throttle shafts with new we also suggest using the throttle shaft seal kits because they will reduce the contaminants that wear out the shafts in the first place. Beyond those things, you may have to look internally. A common problem on 1965-67 carbs is that someone will leave the power enrichment needle out. Check to make sure that the venturi cluster emulsion tubes are free from blockage. Sometimes the idle circuit is simply damaged internally beyond repair - and if several cleanings and rebuilds don't solve the problem you may have to go with another carb.
THE CAR IDLES GREAT BUT THERE IS NO POWER - The engine may even rev up great and seem smooth as glass, until you try to go somewhere. What has happened is that one carb is working and the other isn't. Corvairs run very smoothly as 3 cylinder engines - they just won't have any power.
A WORD ABOUT FUEL CONTAMINATION - An increasing problem with carbs, even newly rebuilt ones, is fuel contamination coming from the gas tank. If even small particles get into the carb, past the filter, you can have all sorts of problems - even a totally dead carb. On cars that have sat for a long time you are best to drain and clean the gas tank and to (at least) replace the fuel tank strainer U-488. See section E for gas tank parts. Sometimes an "in-line" gas filter can be added to avoid future problems.
AND THE FINAL WORD - If you still can't solve your carb problems - then - are you sure the problem is your carbs? The fact is, over 1/2 of the carb "problems" that we hear about turn out to be something else - most often distributor problems. We always suggest checking the distributor out FIRST before you even do anything with the carbs. Bad points or condenser - worm points plates and distributor bushings are quite common and could fool you into thinking you have carb trouble.
REMEMBER - Corvair Underground stocks all available new carburetor parts (including some reproductions) and we carry a big inventory of used parts. And if you don't want the headache of rebuilding your own then send them to us - WE CAN REBUILD YOUR CARBURETORS FOR YOU. DON'T TRUST BIG REBUILDERS - there were over 40 different Corvair carbs and the big rebuilders pay no attention to what they put together. We've also noticed that they pay little attention to worn throttle shafts. I have sent cores to be rebuilt that came back worse than the ones I sent in ! We sell hundreds of Corvair carbs every year and that means that we pay attention to all the necessary details!