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I have a 90 h.p. Johnson manufactured in Oct. 2000 with less than50 hours. Mod.RJ90PLSIG. Ser. G04939675 The top end it turns up 5200 rpm according to the boat tach. It is on a 17 ft Javelin bass boat. The top speed is about 45 mph gps. It has the factory alum prop. Is that about right for top end rpm? I thought it should be higher. Does it need a different prop? Should I have the tach checked to make sure it is accurate? Thanks for any help---Lewis Oerry
what size prop is it?-----ie 13 1/2 * 19"
There are no markings on the prop so I don't know what it is. It measures 7 inches from the center of the shaft to the outside of prop so I assume it is a 14 inch==maybe 13 1/2. No clue what the pitch is. Lewis
Pull off the prop nut. the number should be stamped on the brass part of the hub.
The prop is a 14/19
that's a very good speed for a 90hp. if you change props to a 23" will be too slow out of the hole--rpm's at top will drop to about 4700-4800 this can damage the engine over a period of time by putting to much resistance on the engine. If you change to a 17" you rpms will go up to 5600-5700 (@ wot) 17" will work good for you if you water ski or have a big load in the boat. However you will burn more gas and will not gain any speed
on top end-- 5700 rpms will not harm your engine.