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15hp 4stroke will start but runs on one plug - bouth good spark -bouth plugs are black with asooty deposate after being started and run for a minite-carb mixture? 15hp 4stroke yamaha outboard motor every time you start it ive had three mates have a go at setting carb mixture

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Compressions ok ? 100psi min !

Posted on Jun 10, 2014


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Posted on Jan 02, 2017

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SOURCE: My 2 stroke 3 cylinder carbureted 90 hp Yamaha

Just pull them apart and clean.

Posted on Nov 07, 2010

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SOURCE: tohatsu outboard 15hp 2 stroke was running great,

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

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