Re: Re: 9.9 hp motor to a 15 hp motor ???

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Posted by Chuck ( on August 30, 2005 at 00:00:37:

In Reply to: Re: 9.9 hp motor to a 15 hp motor ??? posted by Spike on August 23, 2005 at 10:54:55:

I am not a mechanic, just a guy that has been around a lot of 10 to 15 conversions because of the many 10hp only lakes in my Southern Illinois Area.

Your best bet is to look up the specs for your make and model year for both the ten and fifteen hp motors.

Generally speaking, the two stroke make model years with the same cubic inch blocks can be converted from 10 to 15.

Some examples are older jon-rude's, japanese made mariners and yamaha's. Nissan-Tohatsu 10 hp motors had larger blocks than the previously mentioned brands and could be be easily bumped up to nearly 18+ hp.

I don't think Mercury ever marketed a 10 that could be converted to a 15. Newer post-yamaha made Mariners were made by Mercury and cannot be converted.

Now for the tricky part. To do the job right, conversion capable Jon-rudes, and Mariners, and Yamaha's need both the carbs and exhaust inserts changed...two stroke motors are very sensitive to exhaust tuning..a fact that many of you may remember if you ran two stroke motorcycles. The fat noisy expansion chamber mufflers really made a difference in hp for the older bikes...contrast this with the noisy but often ineffect muffler or mufflerless conversions popular with v-twin motorcyle enthusists.

I am told that all that is needed to bump a Nissan-Tohastu 10 to 18 plus is a different advance plate. These converted motors are the fastest in my area.

I run a 1999 converted 10hp yamaha on my 16-foot alumacraft riveted jonboat and the speed difference was very measurable and worth the price of admission.

My buddy runs a converted Nissan on this welded 16-foot Polarkraft with a lot more weight and manages 21.5 mph GPS speed to my 20.5 mph gps.

Maybe more information on the make and model year of your motor would help the group help you.

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