acceleration problem

[mrlucky]

1979 johnson will start everytime and will run great until the throtle is pined down dosen't want to plane. Spark is good on all cylinders. Would old lower end lubercation cause this? Almost sounds like the motor is working to hard,

[huntingmaniac45]

Sounds like a fuel delivery problem, old lube woudnt do it. Have you tryed to run some Seafoam thru it? If not....give it a try. Good luck.

[redshirt32]

Some more info is needed before anyone can anwser this for you.
< has the boat ever planed out since you've owned it?
< have you changed props lately?
< You say it runs good until the throttle is pinned. Is it missing or not running smoothly after it's opned up?
< Did someone use the boat and change the motor position without your knowledge?
< Does the tank have fresh gas in it?
Don

[SalmonBum]

It may have spark, but is it a weak spark? Even with a slow spark to one cylinder, it will bog the others out.

If I had to shoot from the hip, either ignition or fuel filter. Both instances a boat will run fine at low rpm, but fuel filter with blockage will not get enough fuel to go wide RPM and will act like its dying. Bad iginition will cause it to run poorly thru "planing" operation, but may run ok once on plane since it no longer needs to work as "hard" to get it to that point.

[john warren]

i would check in this order. fuel tank vent. motor mount/tilt/prop (any changes that have been made for example). fuel filter. spark plugs.carb adjustment.

[b2theill]

that motor has a hub/bushing assy. i would take a look at that if you are having an acceleration problem and the motor feels like it is working to hard.( i am guessing by working too hard you are meaning reving up?) if the hub is slipping the motor will run fine at low speeds until it is put under a heavy load and would not allow the boat to properly plane. g' luck.

[IncredibleHook]

I just had the same issue with an older Merc and it turned out to be a bad coil.