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
