- Do It Yourself Auto Repair
How To Replace Worn Corvair Throttle Shafts
Problems with Idle?
There is a good chance your 40+ year Corvair has chronic or periodic idle issues or other related carburetor problems. If you have sprayed carburetor cleaner into the sides of the throttle shaft while the engine is running and noticed an increase or decrease in the RPMs, the problem is air getting into the carb at this location. This makes a proper idle adjustment a real issue among other things. You may have other air leaks elsewhere. It only takes a little!
The cure is to replace the Throttle Shaft located at the base of the carburetor. The shaft over years simply wears out and thins. Instead of a tight airtight fit when it was new, a minute gap occurs allowing air in and altering the fine air\fuel mixture of the carburetor. You can change the throttle shafts without taking the top half of the carburetor off. Simply lift the whole carb out and tilt it so excess gas can spill out. Once this occurs, you can work on the carb in a tilted manner on a table to access the bottom of the carb where the plate and shaft are. Even if you have never done this, allow one hour per carb.
There are two methods of repair:
1. Buy a repair kit with washers, rubber o-rings and springs to seal the shafts at the carb base.
2. Buy new Throttle Shafts.
Replacing the Throttle Shaft
1.Disconnect the linkage, keep the parts removed in a small cup. Disconnect the fuel line. Remove the the bolts at the base of the carb. Remove the carburetor.
2. Using a small file or grinder, grind off the bent peened end of the plate screws. many plates are not peened and held on with Loctite.Now carefully unscrew them from the plate. Be very careful when backing out the throttle shaft screws. They are peened over on the backside to prevent them from coming out. Take care to shear off the backside of the screws first. Also, use a snug fitting screwdriver to slowly back out the screws while turning them back in every turn until they are out. Taking out the plate screws is one potential problem area. The brass is soft and can easily strip by applying pressure while unscrewing them. If they have never been changed before, you might strip the head before removing the screw. Not a good thing.
It can be easy or hard to remove the plates. If someone before you has had the screws out, they will come out again without any problem. If not, (and you can tell, as you will start to get some major resistance after about 2 turns) simply file off the ends of the screws with a small file or use a high speed cutter in a Dremel tool . If they break off, just drill them out with a 1/8" drill bit. It doesn't matter that you ruin the shafts as you are replacing them. The holes in the plates are about 1/4" so you don't have to worry about damaging them. When you replace the new screws, just put a dab of red loctite sealer on them.
3. Remove the end screw on the shaft.
4. Remove the throttle shaft from carb.
5. You will use the old levers on the new shafts (unless they came with the new shafts). To do this, the lever is removed using a file or Dremel and file the end. Once removed, you weld the old lever onto the new shaft. That is usually the worse problem. I suggest buying the shafts with the lever already attached.
6. You should have new base gaskets.
7. Reinsert the new shaft into the base of the carb.
8. Unscrew the fast idle speed screw all the way out to achieve a good seal with the bore. Usually, this is not an issue. Many settings do not need to be touched.
9. Reattach the throttle plate. If you have not replaced the plates before just pay attention to their orientation or use one as a guide. You must align the chip in the plate with the idle air slot in the base of the carb (that is, where the idle mix screw is). It's not possible to install them backwards if you align the slot. Don't switch plates between carbs. The other most difficult part is getting the plate in the correct position with the holes, they must line-up perfectly. Once achieved, getting the small screws can pose a problem. Once complete, use Loctite to secure them on the shaft.
10. Reattach the linkage etc.