1973 40 HP Johnson Outboard Electric Start Motor can not operate in full throttle

" Gentlemen, I have a 1973 40

" Gentlemen, I have a 1973 40 HP Johnson Outboard Electric Start Motor
After sitting for 3 years, When I took the boat out, the throttle will go up to 3/4 of the way while foward gear before the engine dies out, returning the throttle to the 3/4 position, it will continue to run fine, also idle fine
I've changed a defective fuel line, the brass connector on the tank and cleaned the fuel filter. "no change"
Could it be the tank?
Do you know the type and gap of the spark plugs?
I've put plugs in, but they are the factory gap.
Thank You...........Ralph "

"Ralph... Use Champion J4C or

"Ralph... Use Champion J4C or J6C plugs gapped at .030 . The J6C may give you a better idle.


You've described a engine with a fouled carburetor, in which case the cure would be to remove, clean, and rebuild it. Be sure to manually clean the fixed brass high speed jet that's located in the bottom center portion of the float chamber.

Adjust the carburetor as follows:

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

Joe "