Antique & Classic Cars Blog

In a prior post I mentioned this plan of swapping the top of one classic carburetor with another’s of the same model. That was this afternoon’s project.

If you thought all carburetors of a certain model were the same, you’d be right, if you weren’t wrong. The 4GC–predecessor to the muscle-car era’s “Quadrajet” was used in many GM cars with differences depending on the year, car model, division and engine size.

Carb in the car is clean but with a hack fix by the fuel line fitting, right.

Top of free carb is about the same, with bigger fuel line fitting. The casting is a little different–note three ribs by choke’s butterfly valve lever, lower center (choke missing from free carb).

Mine is from a Buick 215 even though my engine is an Olds. Because I had to create throttle linkage for an engine-swap, I had no existing linkage to worry about.

JB Weld: a blob of this stuff won’t enhance esthetics, but it’s handy.

A “soft plug” (plugging fittings not used in a given application but in the casting for others) fell out of this carb, however, and I plugged the hole with JB Weld, duct tape of the automotive world.

But at the end of the day, I’d rather not rely on the stuff. So the plan was to swap in the top from a 4GC friend Tom Porter gave me when he cleaned out his old engine shop (which formerly belonged to well known MN racer and engine builder, Tommy Adelmann).

Linkage different but nothing insurmountable.

The free one came from a larger displacement application, as suggested by the big fuel-line fitting (and come on, what isn’t bigger than a 215?). Still, the basic shape, size, and mounting holes were the same.

There were enough parts between the two to make the levers work.

Alas, things that appear to be different may be more different. The “new” top had a longer power piston–the rod that releases more fuel when you stomp on the gas. The carburetor body on the freebie must have been deeper.

We were prepared for surface differences but they were different more. Power piston on left is longer, so that top won’t bolt onto present carb body. (It was a real hassle to hold both of these pieces with one hand.)

You can swap out the power piston if you have a new one of the correct size, but I didn’t wanna get too crazy. For one thing, I couldn’t find a threaded barb fitting for my fuel line that mated to the big receptor fitting on the donor carb.

So…the two tops went back to their original homes. There are two more options–buy a scrap 4GC with the same fittings as mine, or take it to a carb pro, drill out the JBWeld and put in a proper replacement soft plug. Car’s running well, so this project sits down on the list.

This entry was posted on Sunday, October 28th, 2007 at 7:35 pm and is filed under Car parts. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.