The engine started surging a few weeks ago and choking seemed to even it out. For that reason, I figured I had a fuel blockage somewhere. I blew out the fuel lines and changed the fuel pump which didn't seem to help, so I hired a tech to check things over and he said he needed to change the fuel solenoid.
That seemed to work for a few hours, but then the surging returned. This time around, the tech cleaned the carb and said he found a small blockage at one of the jets. Again, this seemed to work for a couple of hours and then the surging returned.
The cold engine runs fine, but a couple of hours in when the engine is hot, the surging seems to come back.
#1 get a new tech. You need someone to check the entire fuel system and take the time to run the engine. This guy is looking for quick fixes. I would be looking at a fuel pump issue. when the engine is hot you may be losing your pulse line due to expansion. If there is no clear fuel filter in the line install one to watch to see if fuel is flowing at the same rate, hot or cold.
I would be looking at a fuel pump issue. when the engine is hot you may be losing your pulse line due to expansion. If there is no clear fuel filter in the line install one to watch to see if fuel is flowing at the same rate, hot or cold.
What do you see as fuel flow through the filter, both hot and cold?
#5
xp14629
Sounds more like an air leak from expansion once warm, such as intake gasket or throttle shaft. Check by spraying carb clean lightly around all areas once the surging has started.
Would you elaborate on that? Not sure how carb cleaner works with air leak.
Thanks.
#7
xp14629
If the carb or intake has an air leak, this will cause a lean condition, hince why when u applied the choke, it straightened out. Carb clean is flammable and will enter the engine through the air leak and act as of you were adding more fuel to achieve the correct air fuel ratio. When you spray it around the throttle shaft or carb gaskets if there is not an air leak it will not change how it is running. In doing so remember not to just fog it and spray it everywhere. You are trying to find the leak so use the straw and a light spray around each area. Sometimes wd40 works in a pinch also.
Nothing noticeable to my UNtrained eye while checking fuel flow through the filter. It all looks the same.
With the engine cold, we can run now approximately 30 minutes before it begins surging. Let it cool for half an hour then run it another 30 minutes. I tried it with the gas cap removed and I tried it with the hood removed. Always the same. We finally finished mowing our lawn this afternoon. Whew!
I think the advice regarding some sort of temperature-related air leak makes sense. More sense than, say, a fuel blockage somewhere. Question: In your opinion, how would an electrical "open" affect the engine's running? Would it tend to pulsate like now .... or would it be a more definite stoppage?
Surging up and down would be an indication of a fuel problem. An electrical problem would normally shut the engine down quickly. Checking for air leaks ( which would cause a lean mixture and surging) by spraying carb cleaner around the carb base and where the manifold meets the block, is a good idea. If the engine changes speed you will have found an air leak. You will need to do this when the engine is both cold and hot. Don't think it is the throttle shaft, as it would occur both hot and cold. I am still suspecting fuel pump or pulse line. Please post engine model numbers.
If you can find no air leaks, I would take a look at your valve clearances. They may be to tight, where when the engine gets hot the valves expand and stay open too long.
