got a 16 ft tahiti style boat with a 17p 13?" prop running at 4200rpms, would like to increase rpm's to 5500 range, boat motor is a 71 mercury 1150 tower of power, motor is timed correctly and carbs are sync'd, need a little help here, thanks, Jason
I'm a little outside the tower of power loop but it seems to me a 17 would be about right.To get to 5,500 by prop you would have to drop to an 11" pitch thats a size you would use to push a big pontoon or something very hard to push.
What is the speed at 4,200?Your tach could be off, you could have motor issues,
boat issues,or as combination.Your antivent(cavitation)plate just above the prop should be visable at speed.Usually should measure slightly above the bottom of the boat.In the extreme you could gain 2 to 3 mph and some rpm.Do all the carbs open all the way?Does the boat respond to trim changes.Does the bow come up at speed or does it lay down like its glued to the water.Is the bottom clean and smooth.
Have you done a compression check?Is the motor running on all cylinders?
You wouldn't be the first to not realize a 2 stroke was missing a cylinder especially
on a 6.We have seen new motors with a plug wire off or carbs not opening all the way.
I have had tahiti clones with both an 1150 and a 1500. I agree with Steelspike, something seems amiss. are you sure your tach is right? You should be able to get more that 4200 with that 17 pitch. With no prop ( in the lake or with a prop on and on the muffs in the driveway) can you rev the engine ( only for 2-3 sec) to the Mercury recommended max RPM
of 4800-5300. Not 5500. That would be the 1500 (4800-5800) If so then you have a tune up issue.
You've definately got something wrong. I would NOT go to wot without knowing for sure that the tach is reading right. I have a similar boat and motor, 16' Checkmate and the 115hp "tower" and with my 19" pitch prop for pulling tubers it will rev to 6000rpm easy if I let it. With the 21" stainless prop and trimmed out I'm showing 53 mph and 5700rpm.
That 17" pitch prop is not right for that light boat. What is your speed at 4200rpm?
