Old Johnson 70’s. Full power in neutral but only have in drive

[darrylgood]

Hello, looking for some help here.

70’s Johnson 20 hp.

Can give it full ill throttle in neutral and the engine responds correctly. Once shifted to forward and giving it full throttle, I only get half the power.

engine is also sputtering once in a while when starting it up if that helps diagnose anything.

thanks so much!

 

[racerone]

It only sounds like you have " full power " in neutral.-----It does not have full power.-----Sounds like it is running on 1 cylinder.

 

[hardwater fisherman]

Maybe running on one cylinder.. Giving full throttle in neutral is not a good idea. What is the model number of the motor? I thought the 20hps of that era had a stop preventing from going full throttle in neutral.

 

[F_R]

Maybe running on one cylinder.. Giving full throttle in neutral is not a good idea. What is the model number of the motor? I thought the 20hps of that era had a stop preventing from going full throttle in neutral.

They do have a throttle limiter-unless it has been defeated. IF--IF it actually does go to full throttle in neutral and IF--IF it is running on both cylinders you are in danger of spreading engine parts all over the place, including inside your hide. Don't do that!!

 

[boobie]

Do a cylinder drop test on it.

 

[darrylgood]

Hi all, yes running on 1 cylinder, not the plugs, not the plug wires. Did switch the plug wire to the non firing cylinder and it would not catch. Next step a compression test?

Thanks again

 

[hardwater fisherman]

If you can post a model number or put up some pictures of the motor it should help...Are the plug wires coming from under the flywheel or do you have external coils? Explain what you mean by switching the plug wires. Both spark plug leads should jump an open air gap of around of around 3/8 of an inch.

 

[darrylgood]

Model number J20crcrd

 

[hardwater fisherman]

1984 model. Check spark and yes check compression. if you switch the coils and the no spark follows suspect the coil..