Water on and off on plane

[salmonite]

so i just took my johnson 15hp short shaft to canada and put it on a 14ft aluminum standard transom. My motor pumps water great at low and high rpms in neutral. Then I take off and everything is good unitl I get on plane at full speed. Then it shoots strong for a second then sputters then real strong then sputters.  I never overheated it as I always monitor my tell tale. It pumps excellent as my kicker, What do you think it is? trim it down? transom height? longer shaft?

[EarlyRiser]

I would say it is probably the difference in how far down the intake holes are submerged in the water. When you come up on plane, the top few intake holes are probably up out of the water, so you are taking in some water, but not as much as when you are at low speeds and it is fully submerged.

[Adk1]

yup, you will have to look over the back and see where it sits when on plane.

[salmonite]

well i guess i only go to canada once a year so not really worried about it

[Shellback]

If the motor stops peeing, it's not getting water to the impeller.  It's possible to tear the impeller up at higher speeds and no water. The alarm might save your motor, but not your impeller. Maybe you can row your boat once the impeller goes? 

[salmonite]

Completely understand how a water pump works. There is no alarm as its a 15hp. The topic surrounds more of issues with transom height. The motor works fine on my main boat and other boats I have used with it it at low and high speeds.

[Sk8man]

My hunch is that EarlyRiser was right dead on target with his response.

[salmonite]

Ugh! Went over checking everything except cleaning out the lines... Blew a compressor through it and voila it's fine... Little junk in the line. Odd that it wouldn't affect it at low speeds

[rolmops]

Ugh! Went over checking everything except cleaning out the lines... Blew a compressor through it and voila it's fine... Little junk in the line. Odd that it wouldn't affect it at low speeds

That is the real solution to the problem. The idea about the water intake coming out of the water when planing is pure undiluted hog wash. The water intake on a 15 horse is at the same level as the prop. On plane at  higher speeds it should take in more water,not less. Sometimes there is some crud on the screens or zebramussels just behind the screens and that will cause the above mentioned problems. Just for peace of mind you should still check the impeller because if the crud went past it ,it may have done some damage on the way through

Edited June 15, 2013 by rolmops

[salmonite]

Thanks I will