Johnson 25 will not plain

[James29746]

Hey,I have a 1970 Johnson 25 hp,Will not get on plain.My boat is a 1448 Grizzly Jon.Their is 125 psi on both cyl. New coils,pugs,wires,carb kit and new prop.I tried tilting the motor to see if it would help.The engine will crank with half a pull when warm and two pulls cold.When I open the throttle up it gets speed quick,just will not plain. any help will be appreciated...Thank You

 

[tashasdaddy]

Re: Johnson 25 will not plain

welcome to iboats, what is the weight distribution in the boat. how many people, weight, where are they sitting. is the motor shaft the correct length for the boat. a short shaft on a long shaft boat will not plane. a long shaft has too much leg in the water. what are the wot rpms?

 

[James29746]

Re: Johnson 25 will not plain

It's just me and my wife,I weigh 200 lbs sit center rear,wife weight 120 lbs she sits front center,1 battery,1 six gallon gas tank at the very rear one on each side. Rods and 40 lbs of gear in center.boat is a short transom and the motor is a 15".I don't have a tack yet on the boat.When I put the Johnson on the boat at the first of the year it would jump out and top out at 18 mph on the gps.Every thing has stayed the same except it actually cranks and runs better.I tried a Hydrofoil but it did not help

 

[HighTrim]

Re: Johnson 25 will not plain

It probably has to do with the setup like TD said . Could you post a pic of the stern of the boat?

 

[tashasdaddy]

Re: Johnson 25 will not plain

if the bow is staying high, try moving the tilt pin toward the transom 1 hole, if the bow is plowing and staying down, move tilt pin away from transom. also you might try extending fuel line, and moving battery and tank to the center.

 

[James29746]

Re: Johnson 25 will not plain

Sorry I'm slow getting back to ya'll.I attached a couple of pics,hope I did it rite I'm new to forums.I have moved battery and fuel to the front and back again.I moved the pin,tried every hole and never could get it on plain so I put it in position were it comes up nice but it fells like it tops out just before plain and steering is lite.

 

[jspringator]

Re: Johnson 25 will not plain

Open motor cover and make sure throttle is advancing all the way by looking at the throttle cam. The throttle cam is on the front of the engine. It should go almost to the end of the cam when wide open. Manuel sugggests loss of power if magnito and throttle aren't syncronized. The Throttle shaft linkage might have slipped.

 

[James29746]

Re: Johnson 25 will not plain

I just went out and checked and it's not quite at the end of the throttle cam {at the end of the rise} so i moved the butterfly by hand and that moved the bushing away from the throttle cam about 3/16

 

[jspringator]

Re: Johnson 25 will not plain

Locate the two marks on the throttle cam. When the cam follower roller is centered between those 2 marks, The throttle valve should be closed. Throttle valve should just begin to open when cam follower roller goes past the second mark. Adjust via the throttle shaft linkage screw, under/beside the cam follower assembly, and above the throttle shaft arm. I am getting this from the 1975 Evinrude Service manual for a 25 horse, and should be nearly identical to yours. Mine sometimes tries to bind as it starts the steep rise on the throttle cam; sometimes it takes a little harder turn. I just bought it and haven't cleaned and lubed as thoroughly as I would like.

EDIT: I did mine tonight, and it is easy to mistake the big 2 lines on the flywheel with the 2 marks (dots, really) on the cam itself.

 

[James29746]

Re: Johnson 25 will not plain

Thanks for looking that up!!! I'll have to wait till mourning to check that out. But I remember a few months ago the lever on the carb slipped while on the river,so I tightened it down were it look like it was,I had forgot about that. Thanks!!!

 

[Chinewalker]

Re: Johnson 25 will not plain

If the motor is making power, perhaps you're not running the right prop? Too low of pitch and it might simply rev up and not get over the hump. Too much pitch and it might be lugging. Find out what you had on the 18 and compare it to what you have on your 25. Might even take the same prop...
- Scott

 

[tashasdaddy]

Re: Johnson 25 will not plain

take a straight edge, place it against the bottom of the hull, and extend it out to the motor. the AV plate, should be no lower than the line, and should be parallel with the line. best if higher by 1-1/2 inches. may be the angle, but in the pictures it looks low, and tilted in.

 

[James29746]

Re: Johnson 25 will not plain

I went checked the throttle synchronize cam it was off a little so i set it to what jspringator said.I took another pic with the hydrofoil off.With a straight edge the plait is 1.5" below the bottom of the boat. I have a Jack Plait I can put on to raise it if need be,but it will add 30 lbs?I have a 9x7 prop I am running. I tried a 9x11 but the motor seemed to lug.

 

[James29746]

Re: Johnson 25 will not plain

Sorry, I forgot the pic.

 

[tashasdaddy]

Re: Johnson 25 will not plain

went to Brp site "http://www.evinrude.com/en-US/Accessories/Literature/?popup=true" they show as OEM prop 9x9 and 9X10 prop. 9x7 sure sounds way under propped. also the motor definately needs to go higher, being it is a 1970 i would go 1/2 to 1 inch above the bottom, for water pickup reasons.

 

[James29746]

Re: Johnson 25 will not plain

Ok,I will put on the jack plate and raise the motor and try a new prop.What rpm should the motor run at max throttle???

 

[MikDee]

Re: Johnson 25 will not plain

I concur your motor is too low, I would move it up to about 1/2"- 1" above the bottom as the other posters have mentioned. In this case the hydrofoil would help also, once you move it up.

 

[James29746]

Re: Johnson 25 will not plain

I'll move it up...It would help keep it out of the stumps in the river anyway.does anybody know what rpm it should top out at.I'm going to get a tack today.

 

[jspringator]

Re: Johnson 25 will not plain

5500 sticks in my mind. But if it went 18mph and planed well earlier in the year, but now won't plane, and you haven't changed your set up, I don't see how setup can be the problem.

Get some new fuel just in case.