Small Engines (Lawn Mowers, etc.)/Honda GX 120 Stalling


QUESTION: previously engine ran rough and i cleaned out carb with wire and then the engine was running well. now it has a new problem where it starts on first pull and runs smoothly with no choke and then cuts out with out warning after ~8 minutes. won't restart immediately but if i wait a couple minutes it restarts and runs fine for 2-3 minutes and then cuts out again. each start thereafter only runs 2 minutes or so. if i wait a few days it will run about 8 minutes on first try again. Oil level is full and gas is clean and carb looks ok. it almost seems like there might be an engine temp sensor but i don't think there is. thank you

ANSWER: Have you replaced the spark plug with a new one?
Have the valve clearances ever been checked?

---------- FOLLOW-UP ----------

QUESTION: no and no but those sound like reasons that would cause rough running issues more than the intermittent issue i am having. i was thinking maybe some kind of vapor lock or engine kill switch or something with the electronic ignition. i did submerge this in sea water 3.5 years ago (it is a dive compressor) but hadn't had problems until this summer. i noticed today that the wire that connects to the on/off switch has chafed through so i taped it up and it made no difference.

I used to think the same thing about spark plugs but we see many spark plug fail...even in 4 cycle engines.

You cna check for spark as soon as the engine dies to help determine if the igntion module is failing.  Just have a know spark plug ready and when the engine stops dis-connect the spark plug wire and then connect the new or know good plug and pull the string to see if there is spark.  You will have to ground the spark plug tip of course but the should be a metal engine part in the area for grounding.

Use the address below to find the valve clearance:

Agree a valve will usually not cause this problem but the clearances are easy to check just to be sure they are correct.

Does the engine have a low oil sensor?


Small Engines (Lawn Mowers, etc.)

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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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