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I'm sure this topic was covered before because it might be common. My 53 runs well but a fuel problem has gotten worse. It's sort of like a lean surge but not sure. Truck will run OK around 30 MPH then suddenly back off like running out of fuel then pick right back up again. This happens over and over. Fuel tank has been cleaned and coated, new in tank filter and pickup, new fuel pump, new in line filter. I think it might be the governor on the carb. Read the TM and tried adjusting the governor adjusting screw but no change either way. Anyone have any ideas? I'm going to order a new carb anyway.

To adjust the governor on the carburetor you need a special wrench and a screwdriver. The wrench looks like this:







The screwdriver goes through the center hole while you turn the wrench.

The very end of the carburetor manual explains how the wrench and screwdriver are to be used to adjust the governor.

52 M-42

Some thoughts. If I read the tech manuals correct these trucks either had a sintered type fuel filter in the engine compartment or a filter in the tank in the fuel pickup tube (one or the other but not both). Is it possible that two filters in the fuel line may have dropped your fuel pressure at the carburetor fuel bowl just enough to cause fuel starvation at this operating point around 30 mph (I believe fuel pressure should be 4-5 lbs; I'd have to check the manuals). Another possibility is the float level is set wrong in the carb fuel bowl so that there is not enough fuel in the bowl at a certain point so starvation occurs, you back off for a few seconds and the bowl fills back up, and then going forward the fuel in the bowl is depleted again and the cycle continues at a certain point.
The carburetor manual (the full manual, not the manual with the Carter excerpt) has the procedure for an initial setup for the governor plus detailed data on adjusting it; are you using this to adjust the governor?
Also another thought the carburetor manual says the low speed circuit operates from idle to around 20 mph and both the low speed circuits and the high speed circuits work together from 20-30 mph and the high speed circuit takes over above 30 mph. Could there be something going on with the high speed circuit in your carburetor?