jOHNSON SEAHOARSE 55 NEED BIT MORE SPEED

[nathanfer]

i HAVE HUST BOUGHT A 14.5FT GLASS BOAT WITH REBUILT JOHN. SEAH.55 WHICH IS REBORED TO 60HP. TOP RPM IS 4000REVS. ABOUT 29N. THE DEEP VEE MAKES IT HARD TO PLANE BUT AT WOT THE FUEL CONSUMPTION IS MASSIVE. SI THERE ANYTHING I CAN DO TO REDUCE FUEL CONSUMPTION BUT STILL GOVE ME REASONABLE SPEED? I AM VERY NEW TO THE BOATING WORLD AND ANY ADVISE IS APPRECIATED. THANKS FROM AUSTRALIA...

 

[Cricket Too]

Re: jOHNSON SEAHOARSE 55 NEED BIT MORE SPEED

Hey nat....Are you sure that engine is running right? You should be getting at least another 1000 RPM at WOT. Is your engine propped correctly? That motor shouldn't have any trouble planing a 14.5 ft boat off. The fuel consumption may be normal you might just not be used to it because you are new to boating. 2 stroke outboards( at least carburated ones) use alot of fuel, don't think of it in terms of a car it will never be the same. What year is your motor? I have a 1975 70hp Johnson that is in perfect running condition and gets roughly 4 or 5 miles a gallon at WOT, so you are probably using fuel at a normal rate at WOT. I would deffinetely try to get more WOT RPM's out of it or you will slowly kill it by lugging it at 4000 as well as at lower RPM's. Find out what pitch prop you are running and get back to us, I'll bet if that motor is running correctly and you prop it down a few pitches you will plane off with no problem and get more speed also. Good Luck.

 

[nathanfer]

Re: jOHNSON SEAHOARSE 55 NEED BIT MORE SPEED

Thanks for the tips, The year of man is 79. How do I find out what prop should be on this model motor? and how do I find out what pitch the existing prop is? Also to get to WOT you have to bounce on the throttle lever, I have disconnected and checked the cables, the throttle lever in the motor but no luck. Any advice?

 

[Cricket Too]

Re: jOHNSON SEAHOARSE 55 NEED BIT MORE SPEED

nat....The correct prop is based on what you need the boat to do. In this case it sounds like you need a lower pitch prop for your setup( provided the motor itself is running correctly) to achieve what you want. The prop may be alright for that motor with a different boat or a different load, but with this boat and load it isn't.<br />To find out what you have on it now take a look at the prop and usually there will be a set of numbers either on the inside of the hub or on the outside of the hub. The first is the diameter of the prop and the next is the pitch. When you say you have to bounce on the throttle does that mean you have to hold the lever down to keep it in WOT? And what did you find out when you checked the cables and the lever in the motor? Check the prop and post back. Good Luck.

 

[ChrisCKL]

Re: jOHNSON SEAHOARSE 55 NEED BIT MORE SPEED

Im just a noob but, my idea is a 14.5 ft boat is pretty small for a 55hp ,which weighs quit a lot.<br />Maybe check the realtion to the antivent plate and the boat? should be about 1-2 inches if more than 2 inches it can slow teh boat down and spray alot of water. secondly sinc ehte engine is big on a small boat, the rear of the boat must be deeply in the water causing the head to be high. So maybe change the pin of the engine so that it is slightly less than 90 degrees. i.e so that the prop is slightly closer to the transom of the boat. when running, it will make planing faster because the head will go lower quickly, creating less friction on the boat's body. and it should also make more use of the deep V. and again if this is nto the case, im jus a noob...tryin to help

 

[Chinewalker]

Re: jOHNSON SEAHOARSE 55 NEED BIT MORE SPEED

Incidently, there is no "rebore" capable of giving you 60hp. I would worry about getting all of the rated 55hp before trying to tweak the motor. If the motor was rebored (.ie it blew up and was rebuilt with oversize pistons) your power increase will be minimal at best. Your 4000 revs is WAY low from where that motor ought to be. It wants to run between 5000 and 6000 revs...<br />- Scott

 

[Solittle]

Re: jOHNSON SEAHOARSE 55 NEED BIT MORE SPEED

Take your prop to a prop shop and describe what you have. They will measure your prop and recommend the prop you need (I would guess your motor calls for 5500 rpm WOT).

 

[CFronzek]

Re: jOHNSON SEAHOARSE 55 NEED BIT MORE SPEED

Nate, <br />If it's been rebored that means it also got new pistons and rings. With all those new parts you should nice high cylinder pressures. Why not do a quick compression test. If the numbers are good you'll know the rebuild came out properly and you can concentrate on other issues to get your motor sorted out.<br />Charlie

 

[Yepblaze]

Re: jOHNSON SEAHOARSE 55 NEED BIT MORE SPEED

Running it hard at those reduced RPMs could be detremental, and perhaps was the reason it burned up and required the rebuild.<br /><br />Do not continue to run full throttle at those RPMs.<br /><br />Just my 2 cents.

 

[seahorse5]

Re: jOHNSON SEAHOARSE 55 NEED BIT MORE SPEED

Is it a 3 cyl or a 2 cyl 55hp? Better yet, what is the model number?

 

[nathanfer]

Re: jOHNSON SEAHOARSE 55 NEED BIT MORE SPEED

Thank you for your information. The model is a 79 seahorse 55 2cyl. The prop on it is a 13P and 12.5 diameter. I just cahnged the plugs and new fuel, lubricated the throttle cable and levers, and checked that the fuel filter was clean. I tested it out and no better. Still 4000rpm max revs. Though I could bake of to about 3/4 throttle and still maintain 3900rpm at plane. I checked with a prop shop and they said a 13P prop should be the correct pitch for what I need. So i'm back to square one. The compression test seems like a good idea.