I have a 76 Jeep CJ 7 with a 258, straight six with a 2 barrel carb. If the jeep sits for a long time, it takes a while to warm up and it lurches as i go down the road as if the gas is not flowing completely or the fuel pump is not working properly. Once warmed up, it runs fine. However, the lurching is becoming more frequent and seems to become more consistent at higher speeds. It seems like a gas flow issue, although i have not done any diagnostics to check other issues. Any ideas?
Does the gas you use contain ethanol?
Check that the choke pulloff is properly adjusted.
Does it have an automatic choke? If so, there is likely something wrong with it. It might just be stuck. Or it might not be getting the heat from the riser tube. Or the electrical heating element (if it has one) might be broke. I had a similar problem with my 70’s Ford truck, and there were in fact two problems, both in the carb area. The first was that the fuel inlet valve was sticking shut, and the second was the heat riser tube to the choke had rusted off at the exhuast manifold. Once I fixes those two problem, it has run fine both initially and after it warms up.
The first thing to check is whether the choke plate is fully closed on and immediately after cold starts.
The power valve may be sticking. If you remove the inspection plate on the front of the carburetor and carefully press down on the Y shaped bracket at its base the piston should easily depress with only slight spring tension resistance. If you find that the piston/valve is down don’t attempt to force it. Spray carburetor cleaner at the piston and its bore, occasionally putting slight upward pressure on the mechanism. It would be worthwhile to find a good exploded view of that Carter BBD carburetor. The power valve is lifted out of its bore when the engine is off and no vacuum is present. When the engine is running manifold vacuum draws the piston downward, pulling the needle valves down and restricting fuel flow. When engine demand increases vacuum drops and the valve should rise to allow more fuel to the venturi.
If all that makes no sense to you it would be advisable to find a mechanic familiar with carburetors.
Thanks for all the insight. The butterfly valves on the carb do stick occassionally. I think i will just over haul and give the whole carb a good cleaning.