Johnson Carburetor Question?? Please help!

[Seabiscuit_1]

Hello All

Thanks for all he great info on the site. 6 months ago I had two 1965 90HP Johnson Meteor II motors each with problem that kept them from running. So, armed with a repair manual and naive confidence I completely disassembled them both and created 1 working motor and a lot of extra parts. The ?new? motor starts and runs great. It does however, seem to run a bit rough in the lower RPMs. When I rebuilt the carb I initially set each of the low speed needle valves to ? of a turn open as the repair manual said. It didn?t however explain a procedure for fine tuning them.
So my question is (finally), what is the procedure for getting the carburetor dialed in just right and what do I look for when I tune the low speed needle valves? To complicate things, the carburetor actually has 4 low speed needle valves (1 for each cylinder). The ? open setting is good enough for the motor to run, but I would think a bit of fine tuning of each cylinder would be helpful.

Thanks for the help everybody!

 

[Joe Reeves]

Re: Johnson Carburetor Question?? Please help!

I remember those carburetors well. The following should have you leaning in the right direction. Just look upon the carburetor as being four carburetors.

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

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.

Note: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.

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.

 

[Seabiscuit_1]

Re: Johnson Carburetor Question?? Please help!

Great. I'll try it this weekend. Thanks Joe!