loses power

[red_dragon]

i have a 1969 johnson 115 that runs fine, but after running awhile it loses power but it dont get hot or over heat.and if needed is it worth rebuilding and the trim wont raise the motor when pushing the boat.i

 

[Barnacle_Bill]

Re: loses power

Check your tank vent to be sure its clear. Check all your fuel lines and primer bulb for cracks. When is the last time you rebuilt the fuel pump? Compression? Check fluid level in T&T.

 

[Joe Reeves]

Re: loses power

If you're using a built in fuel tank.......

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vaccum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

- - - - - - -

If the hydraulic unit is actually a Power Tilt Trim unit, the trim operates for only 15°, after that it enters the tilt range which will not hold against the engine's thrust.

If this is what you have, check the fluid level as "bhile" recommends. Also, if that unit incorporates two (2) lift cylinders that set outside of the transom brackets, the problem could very well be a faulty stand up valve that is located in the bottom of the starboard lift cylinder.

If however, the unit in simply a Tilt unit, it is designed for lifting the engine when it is not running only.

 

[red_dragon]

Re: loses power

thanks i will check the tank and have been thinking about putting a new fuel pump in anyway as for the trim it has 2 cylinders on the outside but only one actually lifts the motor.if this is for only lifting when not running can i change that.

 

[Joe Reeves]

Re: loses power

That unit would be a Power Tilt Trim unit of which that problem is usually associated with the stand up valve I mentioned..... BUT keep in mind that the PTT unit will only hold its position under the engine's thrust for that 15° of movement.