To me, that sounds like water in the gas.Just a little bit.Every now and then a bit gets sucked up, and then the engine cant idle on it. At speed it may go through with just coughing,sputtering,or popping.Then its business as usual, until the next slug comes up. You could try some product in the fuel tank which promotes sticksion between the water and the fuel;namely, Isopropyl alcohol.
-The best way I know of to prove it is to pop the top of the carb, exactly when it happens and check the bowl.Fuel and water dont mix. You will clearly see the water as a slug at the bottom under the fuel.The alcohol may do the trick though and save you a bit of trouble. Its not instant though.Read the directions and maybe double the dose.Too much cant hurt at lower throttle/load settings.
-There is another way.But you have to have experienced it to understand what youre seeing. When a mixture of gas and water comes out the main nozzle on a running engine,and hits the butterfly, it doesnt look normal. The water beads up and kinda rolls off the plate into the intake. The beads are bigger than the atomized fuel, and roll slower, tending to stick to the plate longer than the fuel.If youve seen it once youll never forget it.
-Another proof can be seen this way. Take a strong,absorbent,paper towel. Rip a strip off it just narrow enough to pass under the main nozzle, but as large as possible, and long enough to be easily retrieved. Try to lay it flat on the butterfly. Then with engine off, slowly pump the accelerator pump a time or two onto the towel. Wait a minute or two and then retrieve it. The fuel will either pass through the towel or flash very quickly, leaving the water behind, which gets trapped in the towel, and evaporates much more slowly. This method probably wont work on the 2bbls with their tiny venturies, but may on the big 1bbl.
-The accelerator pump and the MJ wells are the lowest points in the bowl and water will accumulate there.If the water passes through the MJ wells at speed with just coughing/popping, but then continues to run, and the water has accumulated in the pump well, then driveaway from the next stop will be very difficult, and the engine will likely stall. But then, since the water has already passed through the MJ well, the engine will easily restart and idle. The proof for this is with the engine stalled, pump the accelerator several times to push the water out and refill it with fuel. The engine may be flooded so expect to start it accordingly. Once running it will driveaway as normal.
-Of course the other mentioned possibilities in this thread are perfectly valid as well. Its just that Isopropyl could be the cheap, easy fix.Happy hunting.
