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Hey folks,
My 18 hp 2001 Nissan 2 stroke engine runs fine at low speeds, idles well and will attain high revs while in neutral. It has problems getting my 14 ft jon boat on plane. Occasionally after much effort the boat will get up and l plane but has trouble maintaining speed. When I got the boat 2 yrs ago it easily got the boat to plane. Today I took the prop off and noticed the nut holding the prop on the shaft was only finger tight but was held in place by the cotter pin. If I simply tighten the nut down would this solve the problem? If not, what else can I check? thanks for any feedback.
 

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Pull the prop off and look at the collar under the prop. You may have hit something or run across a sandbar once and there is a collar inside (between the prop and the shaft/splines) that is designed to "give" so you don't bend/screw up more difficult to replace parts. If this is stripped/compressed you may be losing rpm's on the prop. Doesn't sound too serious if its just that. If you are getting full rpm's from the motor but just not the force out of the prop, this is probably your issue.
 

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Motor RPM's act totally different when under load vs in neutral. The prop the nut on the prop won't cause the symptoms your describing. My guess would be a dirty high speed jet or low compression. Hope it's the munged up jet not low compression. If the motor sat for some time with out being winterized it can cause fine surface rust in the cylinders which buggers your rings up by the time the cylinder is polished again causing low compression. The other thing it could be is a bad plug and or coil. Easy check is to pull your plugs and inspect they should be even in color and tan in color
 
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