dead cylinder 8 hp tohatsu 4 stroke

I have a 8 HP Tohatsu 4-stroke that starts and runs, but has no power. Carb thoroughly cleaned, and when removing plugs, it is apparent the lower cylinder does not fire. What is the short list of possible issues with this seemingly nearly new engine?

Your help is appreciated.

Thanks.

What is your actual model? When did this start? What method did you use to clean the carb? Since it has a siamese coil, and both cylinders fire in time with each other, spark is probably OK, but you could still check for spark for that cylinder. You could have a valve or compression issue, but odds are the carb still has a problem.

pvanv said:

What is your actual model? When did this start? What method did you use to clean the carb? Since it has a siamese coil, and both cylinders fire in time with each other, spark is probably OK, but you could still check for spark for that cylinder. You could have a valve or compression issue, but odds are the carb still has a problem.

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Hi, and thanks for your reply. The motor is new to me, I do not know its history or model number right now, it is at the cottage, I am home. It is the electric start model. I noticed it the first time I started it this Spring. The motor started right off, and idles, but far from vibration free. Motor lags when throttle is advanced, and only for a brief instant seemed to develop full power, then died back, never to run with that level of vigor again.

I disassembled the carb, and used spray carb cleaner and a toothbrush to clean everything, including removing the jets, as I saw done in a Youtube video. Light visibly passes thru all of the small holes in the jets and carb body.

I bought a new set of plugs to try, as that would be a cheap and easy fix if one is bad, but I doubt they are the issue. I will install them this weekend and try.

I can provide model number info this weekend as well when I get to the cottage.

Thanks,

Steve

Probably MFS8A3 or B. The carb needs a Proper cleaning, after a complete disassembly, in real carb dip overnight (comes in 1-gallon cans at auto parts houses), then a thorough spray-out with generic spray. The spray is not aggressive enough to do the job on its own. In stubborn cases, we do the dip in an ultrasonic cleaner. Plugs are never a bad choice; I have been fooled by a few that had issues even from new.

In the future, run non-ethanol fuel, 30 days or newer, and always idle the carb dry at the end of the day, to avoid varnishing.

I changes spark plugs when I got to the lake, and much to my surprise, the motor worked flawlessly. I am thrilled that for once, the cheap, easy fix was the answer!