The Stovebolt Site Forums The Shop Area Engine Shop carbs, mech. advance, rough running 235ci in a 1948 3/4 ton.

Ok, here is the scoop:
I have a 1948 3/4 ton thriftmaster. When I first got it, it idled, but ran very poorly at speed. It backfired, sputtered, and had loss of power. I drove it ~500 miles to bring it home, without a major problem. i figured out on the way home that if I partially choked the engine that it would smooth out the engine at speed, albeit at a gas milage cost. Now a week later, the truck will not idle without being partially choked and still has the same issues at speed.

After reading through various discussions here, I have narrowed it down to either the carb or the mechanical advance. The vacume advance seems like it works, if I turn the dist when running it will pull it back. At least vac advance shouldn't matter in a big way at this point. Here is a list of what I know or have checked:

- the engine was completely rebuilt (.60 over) less than 300 miles ago (before my 500 mile trip), but then sat for a couple years.

- the gas tank was pulled, cleaned and reset, ditto the lines.

- it has a new fuel pump and filter

- new air cleaner

- new plugs, wires, points, cap is new but has a couple chips in the base (suspect?)

- I pulled the plugs after my 500 mile trip with the engine partially choked, and they were very clean, just a light coating of carbon, which wiped off easily with a rag.

- it has a zenith carb from the origonal 216 on it (suspect #1)

I don't have a timing light yet, so I haven't checked the timing, but since the plus were clean and even on each cylinder, I tend to think timing isn't an issue. I have been wrong about timing before though.

here are some basic questions:

-it it worth rebuilding the Zenith carb, or was it never designed for an engine this size?

- If I were to replace the carb what should I look for that I won't have to modify the engine to put on? I'm looking for reliability.

Can you tell by looking at the mechanical advance if there is a problem with it?

Thanks for your advice/help.
Aaron

Look for a vacuum leak at the base of the carb or the intake manifold to head gasket.

Zenith makes an excellent carb; however one was never original on your truck. To determine if the carb is applicable for the 235, we would need to know the number on the Zenith tag.

As a general rule, too small a carb will run too rich up to a point, where it just won't run; too large a carb will run lean (need to add choke).

Jon.

Where is the carb tag? I looked and all I can find is embossed on the carb "Zenith Bendix" on the riser between the carb and manifold insulator it says 961.

check that, I found a little round tag on top of the carb which has the numbers "11275" stamped on the top.

Rebuild the Zenith. If anything, it may be a tad large, not small. Would easily support a larger cam, head work, and improved exhaust if you have the desire to ever make these changes.

Jon.

Is there amodel number or something for that carb? I want to get a rebuild kit but don't know which one, or do all the Zenith kit have what I need?
Aaron

The 11275 is the identification number. You can get a kit based on that number.

Jon.

Any good leads? Everywhere I have looked at Zenith kits, I don't see that number. when I do a search on google like:
"zenith +(carb,carburetor) +11275" I get absolutely nothing. I did read somewhere that if the tag didn't have another set of numbers or letters on the tag that is is an aftermarket carb. Is this true? What carb would be original on a 61-62 235? Will that carb still work ok on a 235 .60 over?
Thanks for all the help.
Aaron

BTW, I checked out This page :-) But couldn't find anything there that specifically listed my zenith carb.