<VV> turbo carbs - long and opinionated

[FrankCB]

Guys,

Continuing on Grant's good advice, some of the YH non-Corvair carbs (Nash, 6 cyl Vette, et al) have a vacuum advance port in the carb throttle body.  This is non-existent in the Corvair YHs.  You can see where it is located on the outside of the carb (in the throttle base) in one of the pics I included in my earlier Turbocharging articles in the Corsa Communique.  If you are using one of these throttle bodies that has the vacuum advance port on a Corvair WITHOUT vacuum advance connected, be sure to plug the outside of the port otherwise you'll get a vacuum leak everytime the throttle is opened above idle speed.  If you use one of these throttle bodies to convert your Corvair to vacuum advance, be sure to check the INSIDE of the throttle bore to make sure it has a small slot (about 1/8 in. by 1/32 in.) which is PARALLEL to the throttle blade.  When the throttle is closed at idle this slot should be located UPstream of the throttle defeating the vacuum advance.  As the throttle is opened it moves to the other side of the slot thereby exposing the slot to intake manifold vacuum and "bringing in" vacuum advance.  I've actually seen a non-Corvair throttle body that had the OUTSIDE connection for the vacuum advance but had NO inside slot so it could NOT produce any vacuum advance.

Frank "likes vacuum advance" Burkhard  

In a message dated 05/24/09 11:05:40 Eastern Daylight Time, gyoungwolf at earthlink.net writes:
I have been following the Carter YH rebuild thread and offer these comments without prejudice (I don't really know what that means, but I heard in on Judge Judy and like it): 
- I have rebuilt about 300+ of these over the past many years and have found about a dozen that could not be rebuilt to work properly regardless of the attention and effort. I even cut one apart after two unsuccessful attempts, but could find nothing out of the ordinary. I think it is probably due to over-cleaning and passage growth or collapse. 
- There are three different size venturis in the 1962, 63/4 and 65/6 carbs. The throttle bodies are all the same size, however. The '62 is also unique in that it used a thin gasket like on the Nash and Corvette and thus had a shorter choke link. You should not use the thicker gasket unless you also switch to the longer rod as it throws off the geometry of the pump stoke. 
- Many of the rebuild kits on the market have a collection of gaskets where the rebuilder is instructed to stack them to the correct thickness. This is easy to screw up as some of the Nash carbs used a 1/8" gasket that is included in some kits so you can use two of them or four of the 1/16" gaskets, but don't mix them. To make matters worse, most kits now use a gasket that was made for the Carter YF carbs. While it will work, it sticks out and looks bad. I guess this is because there are more YF carbs still out there? I order my parts individually from different suppliers, which is the only way I have found to ensure everything is correct (1/16 and 1/4" gaskets, etc.) Stacking gaskets is a bad idea, I think, because they might eventually compress or swell and leak. 
- The accelerator pump circuit design switches back and forth between a ball/spring and brass needle over the course of the years. Yes, I have found both stacked in carbs sent in for repair, as well as needles in the hole for the ball and balls in the tube for the needle. All the springs in aftermarket kits are too long and have to be clipped to size (something the instructions don't mention). 
- The bowl cover for a 65/6 is different and should not be swapped to an earlier carb and vice versa. 
And, Nash and Corvette bowl covers will not work on the Corvair as the vent holes are different. 
- The vent modification (hose connecting the body to the bowl cover shown in a link in one of the notes was also available in JC Whitney catalogs of the era. I have one of them on hand, but I'm not sure it really does anything because there is already a connection between the two (that might simply be plugged, but I could be wrong). 
- The new aftermarket metering rods that have been mentioned have never worked out for me. Every one I have used (and I have tried all sizes) has resulted in a complaint of loss of power, which was cured with a good used rod. I don't know what's wrong with them, only that they don't work when I rebuild a carb using the same specs I have been for over 10 years. I tried to buy them in bulk from the supplier to test and try some modifcations on the tapers, but was told they are no longer making them (yet they still seem to be out there, if you know what I mean :-). 
- I have had good luck changing the main metering jet size by .001 to .002 in just about all cases, while leaving the metering rod the same. (Don't drill them out, buy larger stamped jets). 
- I have located and purchased some aftermarket inlet seat assemblies that have a spring inside the needle to take up engine vibrations that have cured almost all fuel dripping problems. They were originally produced for off road applications, but work perfectly for street use. They were stock in the Corvette carbs when they were first produced. 
- The fuel strainer in the carbs is useless when used with the modern inlet seats found in all rebuild kits. The original design seat was much longer and went up inside the screen, whereas the new ones do not (and so the screen doesn't screen anymore). This is why is it vital that owner keep an inline filter in place. 
- There are 4 passages from the throttle body to the carb which might sometimes be overlooked when rebuilding. If any of them are plugged, the carb won't work right. 
- The little piston in the choke must have clean grooves, as they really do serve a purpose, and vary a signal depending on their position. 
- I don't see much wrong with this carb other than being very sensitive to adjustments. It has been around since 1951, and was used in the Nash, Corvette, Cortez (and other) motorhomes, lift trucks, boats, and in many after market horsepower and racing applications with and without turbocharging. Many owners of early (military style) Jeeps have found it to be a good replacement for their stock carbs due to limited hood clearance. 
- I have also found that a Nash carb works fine on the Corvair when jetted to Corvair specifications. It was the father of the 1962 Corvair YH and is just less expensive and fancy. It has a single heavier spring on top of the pump and slightly different float attachment (like the Corvette), but this does not affect its operation. I can't figure out why GM changed it. 
Hope this helps, and does not confuse the issue further, or raise any ire. 
Happy Memorial Day, 
The Carbmeister, 
A Veteran 
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