Curing 2-cycle Engine Problems





Introduction: Curing 2-cycle Engine Problems

Many 2-cycle engines have problems and are sent to the junk yard before their time. Typical problems include hard starting, rough running, a need to adjust the carburetor during use to keep the engine from stalling, a need to rev the engine to keep it from dying, and not starting at all.

I will assume the user knows to replace the spark plug regularly, to use fresh fuel, and to replace or clean the air filter.

With time and normal vibration, the screws that seal the crankcase from air leaks loosen just a little and air gets into the engine through leaks in the crankcase gaskets.

First check the mounting screws for the carburetor and tighten them. Then go to the screws that hold the cylinder head to the crankcase body and those that cover the end where the crankshaft comes out of the engine. See the yellow circles on this photo of a weed whacker engine. If any of these screws loosen as little as a quarter of a turn air begins to leak into the engine and the fuel/air mixture either is not pushed into the engine on the piston's downstroke or it becomes too lean for the engine to run by pulling in extra air during the piston's upstroke.

After about ten years of use, no amount of tightening on these screws will make a dead engine run. Chances are the gaskets have become hardened beyond their ability to seal the engine. Dismantle the engine completely and install new gaskets. You may not be able to buy the proper gaskets, but you can buy a sheet of gasket material. Use the old gaskets or the engine castings as a pattern to cut new gaskets. Your engine will run like new again.

Step 1: Clean the Exhaust Ports, Too.

Remove the muffler. The exhaust ports are under it. In time carbon residue from the burned oil in the fuel mixture begins to close off the exhaust ports. An engine is an air pump. What cannot get out blocks what needs to get in. Move the piston to the downstroke position (most distant position away from the spark plug) and knock off carbon deposits with a screwdriver. Turn the engine over by hand a few times to blow the carbon granules out of the engine.

Once I used our small 2-cycle garden tiller. After ten minutes the engine siezed and stopped. I had mixed 2-cycle oil with the gasoline, but it was old by the time I was using it. I found advice on the Internet that said to let the engine cool. Then use a wrench with a long handle to slowly turn the engine over. Turn in the same direction, not back and forth. That engine still works very well, although I am sure it suffered a little. Lesson learned: always use freshly mixed fuel.

When a gasoline engine of any kind will sit unused for any length of time, drain the fuel from the tank and run the engine until all remaining fuel in the system has been burned through the engine. This prevents gums and varnishes from closing off small openings.



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2 Questions

I have a champion generator. The plug is good. It fires fine and runs until it gets hot then bogs down. Any ideas?

how to install uncaged needle bearings on 2 stage snow blower crank


Chainsaw engine - I pull the starter and only get one pop, like the egine won't turn over freely. Starter rope OK, took off air filter, took off muffler - same. Took out spark plug, turns over fine.

Any suggestions? Thanks, Mark

Did you check through the engine for problems I mentioned, like air leaks? It sounds like the engine is not getting the right fuel at the right mixture in the right amount. Several things could cause that. Those include air not getting back into the gas tank through the vent in the cap, an obstructed fuel filter, a sticking float (although you likely have a pulsed carburetor with no float), proper mixture screw settings, and no air leaks at the carburetor and engine gaskets.

you posess some excellent knowledge. I am new to this site and I had a question to

ask of you but I am not sure how that is done on this. If you could indulge me and tell me how to do this I'd appreciate it.

Thank you. In my lifetime I have had many problems to solve and little money to pay others to solve them for me. The resolution was to learn what I could and solve them myself. The great thing about Instructables is that we can all share things we have learned or developed ourselves.

Many people ask questions in the comment section just as you did. Others click on the member name and send a private message from the member profile page.

If your question is related to a problem with a motor, check the previous comments to see if it has already been discussed. Otherwise, I am not a professional mechanic. I posted something fairly simple about a couple of problems I had that were almost never discussed. In the old days we bought manuals with troubleshooting charts and worked our way through the charts until we solved the problem. That is still a very good approach, except those charts are now on the Internet and accessible free of charge. I linked one in several comments below.



My leaf blower works fine when sitting on the ground when I pick it up and move around swinging side to side or up-and-down it bogs down and died any ideas

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When it is on the ground the engine is probably at idle, but when you pick it up and swing it around, it is probably with more throttle. Is that correct? If so, swinging it around is not the only thing that is happening. The high side of the carburetor may not be properly adjusted, but the low side is. Look for the letters L and H by two mixture adjustment screws. L is usually open 1 1/2 turns from fully seated and H is usually open 1 turn from fully seated. Those are starting points. Fine tune it after that. It may also be that you have an air leak in the fuel system and the engine is experiencing fuel starvation when you apply throttle. Check screws for looseness. Replace the gaskets if more than ten years old.

I have a style 2stroke strimmer it in runs great but only when air filter taken out any reason for this ?

The engine is not getting enough air when the air filter is in place. Removing the filte increases the air flow. I am assuming you have a filter that uses a pleated paper element. (Some engines in the past used an oil bath filter in which the air had to pass through a reservoir of oil, which trapped the dirt.) Try replacing the filter with a new one. Conceivably you might have too much fuel getting into the engine because of a rich mixture or a heavy float in the carburetor (unless your carburetor uses a pulsed diaphragm rather than a float). In that case removing the air filter also manages to restore the proper air to fuel ratio. If it has been quit a while since you replaced the filter, try that. (Some air filters are a piece of foam soaked in oil. Those also need to be cleaned in soapy water or a solvent and oiled. Drip some oil onto the foam and squeeze it in your hand a couple of times to spread the oil out through the filter.)

i have a 2 stroke engine mounted on my bike and its supposed to run on 16:1 fuel ratio, but i put 50:1 in it, and now my back wheel its connected to wont spin, (btw its a bump start) what should i do to fix it?

I am not trained and have not been employed as a mechanic. I did once run a 2-cycle engine with properly mixed fuel that had become too old. In your case, there was not enough oil in the fuel mixture for the engine's requirements. The two situations are roughly the same. My engine seized up after a few minutes. I did some searching on the Internet. The solution was to squirt a teaspoon of thin oil into the spark plug hole and turn the engine slowly in one direction only with a long wrench on the flywheel nut until it broke free. It is not a guaranteed cure. In my case, it did work. It depends on how much damage was done. My engine seemed to work normally after it broke free.