1990 140 hp Johnson mystery???

[tgerber36]

My 1990 140 hp Johnson outboard has a mysterious issue that I could really use some help solving before I cut the thing off the back of the boat and use it for an anchor!! Ok here we go..it runs great on the hose but wont go over 2000 rpm under load. Fuel delivery is all new including fuel lines from the tank back, fuel pump, carb rebuilds, fuel filter. The ignition has all been checked including the stator, trigger, spark, power pack etc. We have literally gone through this motor to find the issue. The boat ran before with the current prop set up so we know it should run...BUT..it wont go!! oh yea, compression is 125 on all four as well...any new ideas or comments would be greatly appreciated. If I wasn't bald, I'd be pulling my hair out!!!

 

[fireman57]

Re: 1990 140 hp Johnson mystery???

Would your flywheel key happened to be sheared? If you are sure that everything else is right then I would check this. Does the engine just bog? If it does than I would check for spark under a load with a timing light.

 

[HenryB]

Re: 1990 140 hp Johnson mystery???

I did not see where you checked the timer base, but the problem sounds fuelish to me. Fuel flow issues can be frustrating. Do you get the sensation that fuel starvation is slowing the engine down? If ignition is causing the 2000 rpm issue, I once picked up a plastic bag on my intake at 5000 rpm (a 140 same year) and the boat overheated and kicked in the S.L.O.W feature and the engine dropped to 2000 rpm. I thought the engine was a goner the way it choked and bucked at anything over 2000 rpm. I would think if your problem were with the S.L.O.W feature it would be noticeable. Try running on an auxiliary tank. You may have a pickup tube or tank vent issue. If it runs on the aux. Tank try removing the gas cap for effect (for checking the vent).

 

[jpendergrass]

Re: 1990 140 hp Johnson mystery???

My 76' 135 was the same way from previous owner rigging the throttle cable. Check to be sure timing is advancing along with throttle as it should. A new set of cables and timing got mine running great.

 

[V153]

Re: 1990 140 hp Johnson mystery???

I would double check spark. Sounds to me like it's hitting on 2 cylinders. Particularly when you say it runs great on muffs. I guarantee that even the best trained ear can't tell if these motors are firing on 2 or 4, just by listening to it run on muffs.

Yes, do a link'n sync by all means. Make sure your butterflies are opening all the way, etc.