Johnson 75 (84) won't run in gear, but runs fine when I gain speed in neutral

[Syntax]

Hi all.

I have a Johnson 75 hp, 84' model that won't run when I set it in gear; It dies out almost immediately when I try to give it speed. However, when I have it in neutral, it runs fine when I gain speed. Any idea what might cause this? Adjusting the carburetor and ignition to "standard" seems to have helped a little, but it still feels like there is something that is pretty wrongly adjusted.

Any guidance is highly appreciated.

 

[racerone]

That motor will sound " fine " in nuetral to the untrained ear.----Means nothing as it will sound fine on 2 of 3 cylinders.-----------Gather the facts on the motor with a compression test.---Then check if spark will jump a gap of 3/8" or more.

 

[Syntax]

Compression shows 7,0 - 7,2 - 7,6. Spark is also fine.

 

[glenn property of pam]

if that's bars that's about 102 to 110 psi. now spark test was done over 3/8 inch or did you just check at the plugs?

so next is fuel. when was the last time the carbs were rebuilt and has the original fuel pipe ever been changed out.

 

[Tim Frank]

Spark is also fine

Not much to go by there...ummmm....maybe it's not "fine" enough.

 

[Syntax]

Spark shows 0.30-40 inches in the opening. Tried to adjust the "arm" right below the flywheel to see if the igiton was badly timed, and it sure was. The engine now runs alright when I set it in gear. The engine still runs a bit uneven, and i'm assuming this is because the carburetors need some adjustments or even an rebuild.

 

[Tim Frank]

Spark shows 0.30-40 inches in the opening

??????
OK, this should not be so much like pulling teeth.....I'l try one last time. ...How did you verify the spark?

 

[F_R]

Spark shows 0.30-40 inches in the opening. Tried to adjust the "arm" right below the flywheel to see if the igiton was badly timed, and it sure was. The engine now runs alright when I set it in gear. The engine still runs a bit uneven, and i'm assuming this is because the carburetors need some adjustments or even an rebuild.

You messed with the timing? I hope you used a timing light and did it correctly. If not, possibly good-by motor when the pistons melt.

 

[Syntax]

Timing light was used.

Apparently the timing wasn't the main problem. When I tested the engine in the ocean, the same problem as before happend again- it dies out when I gain speed in gear. So I tried to adjust the carburetors another 3/4 open, and this really did it. The engine was just hungry for more fuel.

So to me it seems that "turn 1 1/4 form lightly seated" won't always do the trick for old engines since the seal around the screw might have gotten harder or something. Or maybe the carbs just really need a rebuild?

The engine is supposed to have around 5400-5500 rpm at full speed, but I only managed to get 5100. I read that this can have numerous reason, like the propeller. I will try to adjust the carbs some more tomorrow while running at full speed.

 

[nwcove]

....geez, if yer getting it to spin up to 5100 yer running ok. keep a close eye on the condition of the spark plugs , and enjoy it . jmo

 

[Tim Frank]

I will try to adjust the carbs some more tomorrow while running at full speed.

​Unless I am completely misunderstanding what you wrote, I think you have just turned left and the parade is turning right.
I believe that the high speed jets are fixed on that motor....the only way to "adjust" them is to R&R them with one size bigger or smaller....you have to be REALLY good to do that "while running at full speed."

You CAN remove them and clean them thoroughly.....which may be much of your problem.
You didn't bother saying whether you've had this motor for a while, and this is a new problem,.....or whether it's a new-to-you motor and hasn't run properly since you acquired it.
Makes a difference.
If it is new to you, when you remove the jets to clean them, make sure that they are the correct ones. There is no guarantee. People mess with that stuff all the time.

edit : BTW, should be 56D orifices.