1977 75HP Johnson, stalls in Fwd or Rev

mtf302

Recruit
Joined
Sep 21, 2008
Messages
2
I'm new to this forum and I wanted to start by saying i'm impressed with level of expertise that can be found throughout. :)

I have a 1977 Johnson 75hp Stinger. It ran great up until about 5 years ago, when it started stalling from neutral to Fwd or Rev. At that time, we had new pistons put in (because compression was low) and the carbs were all rebuilt. The shop ran the motor in the tank and said all was good. We took it to the lake and could not get it run under load. After spending 1500 dollars on the rebuild, I put in storage where it sat until just recently.

Six months ago, I pulled it out of storage, took it to the local repair shop where they found a lower end gasket bad. They said it was leaking water into the number 3 cylinder. They replaced the seal, cleaned the carbs, put new plugs in, ran it, and said everything looked great. Alas, I get the boat back into the water and it idled fine (about 1000rpms) but soon as you engage Fwd or Rev, it dies. After about 45mins of messing with the throttle, I finally got it to go, with no problems, but soon as you stop and put it back in neutral, the same problem occurs.

Last month, I replaced every electrical component I could find..ie. coil packs, brain, fuses, pickup under the flywheel (out of sheer desperation), checked all wiring, replaced the plugs again, had the carbs cleaned and adjusted again.
I had the techs run it in a tank...ran fine. It runs supurb on the ears and in a tank...just not when the boat is in the water. Almost everything on the motor is brand new or rebuilt. The linkage is new and has been adjusted by many mechanics. The fuel system is new, including fuel pump, hoses, and the pickup screen. The water pump is also new. Took it out last week...and no shocker here...started right up, warmed up for 5mins, put in Fwd...and it died. Theres about a 40% chance of getting it to not die when its put into gear and then it runs great.

Sorry this post is so long, but after 4 boat shops, 3000 dollars, and countless hours of myslef trying to figure out what is wrong with this motor, i'm about done with it. Any advice or information would be greatly appreciated. Thank you :)
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Re: 1977 75HP Johnson, stalls in Fwd or Rev

What is the model number of that engine?

What compression does that engine have at the present time on the numbered cylinders?

With the engine in perfect condition, the idle (on a flushette) should be 1000 rpm for a 20" shaft engine and 1200 rpm for a 25" shaft engine.

Has anyone changed the linkage between the cam and the vertical throttle arm?

Do the throttle butterflies open and close fully at full throttle and idle? They must be in synchronization.

The throttle butterflies should just start to open when the scribe mark on the cam aligns dead center with the throttle roller. Does it?

When you cleaned the carburetors, did you manually clean the high speed jets that are located in the bottom center of the carburetor float chambers? If not, do so as they are very prone to clogging and cleaning solvent usually doesnt do the job thoroughly.
 

mtf302

Recruit
Joined
Sep 21, 2008
Messages
2
Re: 1977 75HP Johnson, stalls in Fwd or Rev

Thanks for the quick reply. I won't be able to get to the boat until this weekend and I don't have the model number on hand. Thanks again for the info and i'll get back to you.
 

txbandit44

Petty Officer 2nd Class
Joined
May 11, 2008
Messages
182
Re: 1977 75HP Johnson, stalls in Fwd or Rev

Did this ever get fixed I have the same problem. Runs great out of the water on muffs but dis as soon as you put in the water and try to enguage fwd or rev.
 
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