The son's 6 HP Tecumseh go-kart engine wouldn't start at all this morning. That didn't really suprise me since it hasn't been run but once this past September after not having started it for the previous 7-8 years. It wouldn't start initially but I got it to run then by disassembling the carburetor and giving it a good cleaning with carb cleaner. It ended up that two of the three small fuel holes in the nut that holds the bowl on were clogged. It ran pretty good that day afterwards. I added Stabil (gasoline stabilizer) to the gas and ran it like that for some time afterwards to get the Stabil distributed throughout the fuel system.
So today, two months later, we were going to sell it so the son and I went out this morning to make sure it would start and run ok. Nope, not at all. After priming it and pulling the cord umpteem times, it would only run for a second or two once in a while So after much frustration, I took the carb apart again and cleaned it but there really wasn't much varnish that I could see. I finally noticed that the float inside the bowl seemed to be hanging up on the sides of the bowl so I cleaned both with a brush and more carb cleaner.
So now it starts but only if we hold the gas pedal down about 1/3 way. While the son held the pedal down to let it run and warm up, I used the rest of the carb cleaner to spray while the engine was running hoping it would find something gummed up with varnish.
The engine is surging about every 2-3 seconds and I can see the choke opening and shutting with the surging. If we let off on the gas pedal, the engine dies.
Spark plug is like new, checked its gap and I wire brushed it to get it bright and shiny at the gap. It wasn't really bad even when I first pulled it out, no evidence of fouling or fuel on the electrodes.
So with the rhythmic engine pulsing and its inability to idle after sitting for 3 months, anyone have any ideas? I swear the carb is sparkling inside and outside. Carburetor adjustments have not been screwed with and the idle screw is set properly.
Drain the gas. Modern 10% alky gas doesn't last but a few weeks and can pull water from the air like brake fluid does. Drain it and try fresh.
Sorry I should have mentioned I drained all the gas this morning and flushed the lines and carb with fresh gasoline which didn't help. It's ok now though, I dropped the price a little and am now selling it to a guy who knows it doesn't idle well.
Most likely the idle circuit is plugged. The engine runs off the idle circuit even at full throttle if it isn't under load. The surging is happening because it is starving for gas off the idle circuit, so the governor opens the throttle plate to get the engine back up to speed, and it pulls off the main circuit and speeds back up. When the plate closes again, it starves for fuel and it starts all over again. On the side of the carburetor, right above the lip of the fuel bowl, there is a jet (assuming its a fixed jet unit from your description) that can be removed and cleaned. It probably has a small plastic cap over it that you can pop off. The jet will unscrew and you can blow carb cleaner and compressed air through it. The metering hole is on the very tip of it, and its pretty damned small (something like .005" iirc). I usually blow carb cleaner back into the hole it screws into in the carb to flush that out as well. When you screw the jet back in, make sure it is tight, but don't twist it off.
The above is assuming you have a newer fixed jet carb. The bowl nut (also the main jet as you said) will be smooth on the bottom with a number stamped there identifying the jet. If it was an adjustable jet carb, there would be a screw sticking out of the jet with a spring on it. The idle jet that I mentioned above would also have a spring on it and would just be a sharp pointed needle. They stopped using those carbs 15-20 years ago due to emissions regulations.
Another possibility is that the carburetor bowl vent is plugged. Some vent back into the air cleaner housing through a hole or through a small tube that sticks into the housing a short ways (usually red). Others vent through a very small hole in the side of the carburetor. This hole is usually on the same side as the idle jet and is right below the flat "boss" that has the carb id numbers stamped on it. Blow carb cleaner through it if you find it.
I work on small engines at my job in town, and I must have cleaned 20-30 carbs already this season on snow blowers with the exact same problems you are describing. When storing a 4 cycle engine, you should fill the fuel tank 100% with fuel and stabilizer mix, let the engine run a few minutes to get the mix to the carb, then shut the fuel off and let it run dry. You'll run into far less issues that way. Our engine distributor has been recommending running premium fuel in all small engines to help offset the problems caused by ethanol in the fuel. In storage, the ethanol separates from the fuel and absorbs water, causing all sorts of problems with carbs and whatnot. That's why you want a full tank of fuel. There is no room for condensation to form in the tank if its full of fuel. If you can find fuel without ethanol, use that. There are a handful of stations around here that sell one or more grades without the ethanol. Also, never run fuel with more than 10% ethanol in any small engine. All the manufacturers we deal with will void your warranty if you do. Another tip is to use a marine grade fuel stabilizer (we use Marine Grade Stabil) to help deal with moisture and ethanol issues.
2000 WJ Grand Cherokee Limited, 4.7l V8, Quadra-drive
Farming is easy when your plow is a pencil and you are a thousand miles from the cornfield. -Dwight D. Eisenhower
Don't curse the farmer with your mouth full.
Ah, cows. A thousand roast beef sandwiches wrapped in a gorgeous leather coat.
That was awesome information Country Boy, thank you VERY much. I cut and pasted what you said into an email to the buyer of the go-gart so I'm sure your information will get it running well again for the new owner. Thanks!!!