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Tohatsu outboard 15hp 2 stroke was running great, suddenly won't power up under load. new tank, new hose, new fuel,new plugs, carb cleaned all ports clear no change in operation. Engine will start fine, idol fine. when any throttle is applied the engine boggs down, runs very rough and provides no power or increase in rpms. Squeezed fuel bulb with no change. Using a rag removed the spark plug wire, felt the spark, engine soon quit. tried both cyls.

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First: with flashlight or mirror look down the carb- with switch off- and gear and throttle wide open and see what the butterfly valve inside there is doing. It should be parallel to the air flow.

If not you need to find the actuator am and be sure it moves with the control and opens all the way.

Next make sure the timing plate under the flywheel moves at the same time the throttle is opened. Then -using timing light- see if the timing is set to the correct "wide Open throttle" - this is a 2 man job done at sunset with good marks on the flywheel (don't wear a tie). This can also be done static by running it out of gas and using the pull cord- if it has no safety interlock.

Last- and the saddest part- is the compression test. The strength of the reading is not as important as the similarity. When I worked on Chryslers, they were bad if the two readings were as little as 8# apart. The minimum reading should be over 80#.

Posted on May 26, 2011

  • tomkaren428 May 27, 2011

    Very good info. Compression 109/110. Butterfly open/correct. Spark test jumps 1/2 inch. Timing may be the issue, check that this wknd. Not really sure how but will figure it out. Thank You!

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