1976 Johnson 50 HP Desperate need help

[banchigu]

Hello Folks: I am in desperate need of your help. I have a 1976 Johnson 50 HP, that was running great, my buddy took it off his boat and it sat for about 4 months in his garage and I bought it from him. When I installed it it would not hit WOT and would only go about 25MPH on a 16.5 foot tracker. So I tore down the carbs and it ran a little better.

My buddy then tore the carbs again and now it will accelerate really good but once it hits 15mph it bogs down and does this accelerate and decelerate thing, hard to explain it goes fast then bogs down. As long as I keep it under 12 mph it runs fine, it also idles and reves up fine.

Now if I pump the priming bulb it works better but eventually I have to cut back on the throttle and start all over again.

I have checked all the lines, changed the priming bulb, cleaned the fuel pump and still no solution, spark is good, compression is also good.

Desperate...

 

[Bosunsmate]

Now if I pump the priming bulb it works better but eventually I have to cut back on the throttle and start all over again.

That indicates your fuel pump is bad. You should check your fuel tank breather is clear too.
Is your primer bulb holding firm with the engine off?

 

[gm280]

Seem Bosunsmate hit the nail on the head. I too suspect the tank vent if the primer bulb is good. But I also think there still is a carb issue as well. Because every time you cleaned the carb a different range of throttle seems effected. Maybe another carb cleaning with a good carb kit installed. But don't just spray some carb cleaner at it and go on. Disassemble every circuit on the carb. So many times folks neglect to remove needles and jets and never ever clean the tiny little holes and slots and the carb will never function correctly until everything is clean. So maybe once more with carb spray and compressed air and even a piece of fine copper wire to slide through all the passage to verify they are open and clear, and a carb kit installed as well. Make sure the float is good and not soaked with fuel... JMHO!

 

[banchigu]

Here are some videos.

How the engine hesitating at 15 mph.


When I pump the bulb.



When I put the boat on the trailer I pushed it to WOT for a minute or so and it did not hesitate it actually moved the car forward a bit.

 

[banchigu]

That indicates your fuel pump is bad. You should check your fuel tank breather is clear too.
Is your primer bulb holding firm with the engine off?

I changed the fuel pump and still the same, priming bulb holding firm, and cleaned pick up assembly.

Still does not work.

 

[bonz_d]

Also check the gasket behind the fuel pump to the engine. If it is sucking air the pump will not work correctly. The pump runs on vacuum pulses from the engine. Then check the float needle valve. I had a 1975 50hp that the needle would stick. I have seen 2 types of needles for this engine, one uses a small clip to the float while another does not. The one w/o the clip is the one I always had trouble with.

 

[ondarvr]

The 1975 was a 50, I think in 1976 the 50 was upgraded to 55HP, I had both, but they're almost identical. Check for air leaks in the fuel line, the connectors are a common point of failure.
And crud in the tank will plug the carbs almost immediately again after cleaning them if you don't have good filter in place.

 

[banchigu]

Thanks guys I will check those things tomorrow.

 

[bonz_d]

The 1975 was a 50, I think in 1976 the 50 was upgraded to 55HP, I had both, but they're almost identical..

Indeed. the 50,55,60 and even the later 40hp were all basically the same engine with changes to the carbs and choke/primer setup over the years.

 

[Dmpaul89]

water in gas?

 

[banchigu]

Found the problem a float was upside-down. Now it runs like a scalded cat, but after running a few minutes it begins to sputter I cut back on the gas and then it will run like a banshee again

 

[bonz_d]

Good job. Sounds like you still have a bit of a fuel issue with the bogging.

 

[fireman57]

go through the high speed jets again. Sounds like you picked up some crud in the tank. do you run an inline fuel filter? Also, put a half can of Seafoam in your next tank of gas.