1973 Johnson 140 loses power

[Fishin Dan]

I recently repowered with a 1973 140 johnson. The first time I took it out it ran great, until I would turn the boat, it would slow down, when I straightend out it ran fine. The next time out it would thottle up and plane out--after a couple minutes it would slow down to approx 2500 rpm from 4000. As I played with the throttle it would speed up again and then slow down. If I put it in neutral and push down on the throttle it would rev up to about 4500-5000 rpm, after 15 seconds it would slow down to 2500 again. If I hit the right spot with the thottle--approx. 3000 rpm it would somewhat maintan that speed. I took the carbs off and apart and cleaned them up. They did'nt appear to be very dirty. The 2 spark plugs on the right side (standing behind the motor) are cleaner than the other side. I'm getting good spark and even changed the power pack, still the same results. Did a compression check and all 4 cylinders were right at 110 psi. Changed the fuel line and tried a portable tank, with no luck. I'm hoping one of the forum members has suggestion!!!!
Thanks for reading. Dan

 

[OBJ]

Re: 1973 Johnson 140 loses power

Hello Dan and welcome!

From your post, I would guess your losing spark to the two starboard (right) holes....even though you changed out the power pack. If you have access to a timing light, next time out, check the spark to these two cylinders when the engine slows down.

Slowing down in a turn is interesting. Did it make any difference which way you turned? Also, take a look under the flywheel at the leads coming from the timer base. Brownish colored wires if I recall right. Should be two on the port side and two on the starboard side. Make sure these wires are in good shape and not frayed and going to ground.

Is 4000rpm all your getting at WOT? If so, you need to check the set up of the engine on the boat and prop the engine out to get at a min. 5500rpms at WOT. 5800 would be better yet. Low revs at WOT lug these engines. Too much heat and premature death.

And it's not a good idea to rev the engines up to high rpms in neutral. Can cause a run away.

Well....this is a start. Maybe one of the other guys will jump in here and lend a hand.

 

[ezeke]

Re: 1973 Johnson 140 loses power

I would like to understand more about the motor.

Maybe you could give the model number. I don't think that 1973 could be correct.

 

[OBJ]

Re: 1973 Johnson 140 loses power

Spot on ezeke.....140's didn't show up till 77'.

 

[DHPMARINE]

Re: 1973 Johnson 140 loses power

And 1978 140HP had 2 power packs.

DHP

 

[ezeke]

Re: 1973 Johnson 140 loses power

Maybe its a 135 from 1973. If it is you might want to replace that cylinder head gasket. Also, make sure that the grounding strap on that right side is very clean and in good shape.

Clean all of the connections on the coils, especially the grounds.

What spark plugs are you using?

 

[OBJ]

Re: 1973 Johnson 140 loses power

Why don't we all get together and open one big engine repair shop?? Hawaii comes to mind for a good location. 8)