Newbie needs help - 1976 Johnson 55

[Mr Dormouse]

Good afternoon,

I have an old 1986 15' bowrider that has a 1976 Johnson 55hp outboard motor. I know nothing about boats and all my mechanical experience is car related. Here's what is going on...

I had asked a local shop to give this engine a once over/ diagnostic as the boat seemed terribly underpowered on a calm lake. They said the carbs needed cleaning so I had them do it. A total of $600 later I have zero improvement in the performance of the boat.

- Eng idles nicely
- The fuel filter is clean
- When I took boat out after "repair" I noticed the water separator was the same so I bypassed it and the power increased a little (not much though)
- Fuel tank is clearly homemade
- When eng is full-throttled it wants to stall for a second
- Boat moves like it weighs 10,000 lbs
- Has rooster tail though
- Fuel line is clean

I need assistance. Any ideas?

Cheers,

Mr Dormouse

 

[Daviet]

Re: Newbie needs help - 1976 Johnson 55

Do you have a tach in the boat, do you know what the WOT rpm is?
Have you checked the compression and spark?
Does pumping the primer bulb constantly help?
What plugs are in the engine and what is their condition?

 

[Mr Dormouse]

Re: Newbie needs help - 1976 Johnson 55

Hello & Thank you in advance.

Do you have a tach in the boat, do you know what the WOT rpm is?

- The tach does not work. I do not know what "WOT" is though.

Have you checked the compression and spark?

- Compression is 120 & 118. Spark seems good as she starts right up.

Does pumping the primer bulb constantly help?

- Yes, but you really have to work it to get a nominal difference.

What plugs are in the engine and what is their condition?

- Plugs are new. Champion QL77JC4 @ .040 gap

Mr Dormouse

 

[Daviet]

Re: Newbie needs help - 1976 Johnson 55

WOT=wide open throttle
If pumping the primer bulb helps it might mean you have a fuel pump problem. Do you think you could check fuel pump pressure and flow to see if the pump is working correctly?
You could use a timing light to see if you are loosing spark on a cylinder under load. Have someone run the boat for you and check eack plug wire for spark. If you don't have a timing light you could remove one plug wire at a time and see how the engine reacts. Be careful and use a set of insulated pliers to pull the wires, you can get a healthy shock from the plug wire if you are not careful.

 

[Mr Dormouse]

Update

Update

Okay, so, knowing I have to check RPMs I recalled the seller had said the rectifier was on the fritz so I have replaced that.

There is an unconnected short grey wire which I believe is from the tach. If so, should this share a terminal connection with one of the rectifier yellow wire, the red wire, or have it's own spot on the terminal?

I have also replaced the water separator.

Fuel pump is on the way as well.

The fuel tank is homemade and the guy did a lot of shoddy work on everything else... for example he cut the thermostat after it baked in place... so, since I cannot tell if the fuel uatake has a long stem on the inside of the tank (as everything is welded shut) I am going to switch out the existing 6 gal with a portable 6 gal just to be sure there are no issues there.

Cheers,

Mr. Dormouse