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nmantas

Indication of unmixed gas

nmantas
12 years ago

I know that unmixed gas in a 2 stroke is going to be indicated by major compression loss and a nonrunning engine. What is an indication there is mild damage (without a compression test)?

I have the opportunity to buy a lawnboy with the duraforce engine rather cheaply. The only hitch is that it runs for a minute then stalls. I can handle cleaning and, if needed, rebuilding carbs but I don't really want to get into cylinder/ring work.

I haven't went to go see the machine yet but was wondering if there were easy tips to checking it such as seeing/hearing the way it stalls out, etc that would be a clear-cut indication of unmixed fuel.

Thanks

Comments (5)

  • rdaystrom
    12 years ago

    If a 2 stroke has been run much on unmixed fuel the most likely first failure would be a piston seizure. They never fail exactly the same twice but you can almost be sure that the engine would be quite noisy if they managed to get it loosened up and going again after they discovered their mistake. The noise would probably be a real "ringy dingy" sound of piston slap on the cylinder wall. A seriously damaged engine with a lot of piston and/or ring damage would be quite noisy, have little compression, and would likely struggle to run well and have little power. The symptoms you mentioned of stalling after a minute could be a coil going out. Check spark after it dies. Your assumption of probable carb problems is right on as well.

  • 1saxman
    12 years ago

    I doubt if the stalling is related to straight gas or a bad coil. I would look for clogged exhaust ports and leaking crankshaft seals. These engines have much lower compression than a 4-cycle - about 90 psi is the minimum compression. If exhaust ports are clear (you have to remove the cover to the transfer pipe under the deck, then the transfer pipe to see the ports), you have to look at the crank seals. Expect some oil and black goo around a good seal. A bad seal will be even wetter with fuel/oil. The crankcase has to hold vacuum and pressure for a 2-cycle to run. Sometimes the pressure will pop a seal up out of place and it can simply be re-set.
    Typically, a bad coil is evidenced by a no-start condition but it's not impossible that it start, then lose spark.
    On the compression, A Duraforce in good condition will spin rather freely if you take off the plug wire and pull the starter. It's not at all like a 4-cycle. A running engine can take over 5 seconds to coast down if you cut off the ignition without engaging the engine brake.
    Also, the air filter is critical. If it's clogged up with dirt/grass, etc., the engine may not be able to get enough air to run. It has to be washed, dryed and oiled.
    If the mower starts but then tries to cut off, put it back on 'choke' and see if it keeps running. This would indicate a blockage in the fuel system in the carb.

  • ewalk
    12 years ago

    I tend to agree with RD In a 2-stroke scenerio either a bad coil or fuel restriction from ethanol fuel or just stall gas will give the symtoms that you have indicated . A valid compression test will verify the engines overall current condition. As for testing the coil once the engine indicates the symtoms is the time to immediately check for a good blue spark . Good luck :)

  • nmantas
    Original Author
    12 years ago

    Thanks for all of the input. Another person that has seen the mower thinks its the coil....which would make complete sense with the Duraforce coil history. I'm going to give it a few more days to think about it before buying.

  • rustyj14
    12 years ago

    I have heard those engines make very good boat anchors!
    Especially those that have been run on plain gasoline, not the oil-gas mix!