Yamaha 2 Stroke 30HP won't rev to full throttle

I have a 2 Stroke Yamaha 30HP that is about 7-8 years old (I could confirm if that will help). It is mounted on a tinny we bought about 5 years ago but has still down very little work. Gets used for about 3 weeks each summer then it's back in the should for the year. Engine always has and does start with no trouble even after sitting for 10-11 months unused. Also runs smoothly and does not cut out. Last time I used the tinny I noticed engine was not reaching usual full throttle speed. I pulled engine cover off and checked out the throttle cable, linkages and air filter. I don't see any obstructions and it seems that full throttle position is being reached (at least by eyeballing the carby linkages and butterfly) when I open the control lever full tilt. I'm a lot more familiar with motor-cycle engines than outboards but I'm a reasonable back-yard mechanic and understand the principles of what we are dealing with here. So for you guys who are more familiar with the ins/outs of outboards does this sound like a familiar problem? Does anyone have any suggestions, other than to trailer i to a known outboard mechanic?

Is the motor stored with the carburetors empty ??

racerone said:

Is the motor stored with the carburetors empty ??

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Thanks for the response. Answer is no, last thing I do is run the motor with fresh-water hose flush, then I park it in the shed. I have never had a problem starting the engine up again, even after a long break (10 months). I do flush the fuel tank and use fresh fuel at start of each summer so it's not last years fuel - except what's left in carbie bowls. I guess you are suggesting I should run the motor dry before storing, rather than turning off ignition. Is that the suggestion? Is failing to do this likely to be the cause of a motor that runs smoothly in all other respects, but will only reach about 90% full throttle revs?

I have a similar problem which I have just posted on this forum and just saw this after. Did you ever work out what your problem was ?

Hi Reno62, sorry for slow response. Just saw this in my queue. I did work out my problem and am embarassed to say it was nothing to do with the motor. It was just a thin film of barnacles that were on the hull, so thin I thought would make no difference, but scraped them off and performance completely back to normal! Lesson learned!