How do you adjust idle speed 1991 johnson 100 hp
not important, what's important is that they are absolutely clean, including the four brass high speed jets located in the bottom center portion of the carburetor.
That model engine's carburetors has fixed jets, BUT if the slow speed jets are adjustable, earlier model carburetors have been installed. If so...................
The four adjustable needle valves control the flow of fuel in relation to the set air flow, adjusted as follows (if needed).
(Dual Carb V/4 With 4 (2 each carb) Slow Speed Adjustable N/Valves)
(J. Reeves)
The adjustment procedure of the carburetor slow speed needle valves follows. NOTE... if the needle valves turn too freely, replace the nylon bearing retainer (the nylon item at the front of the carb that the needle valve goes through first) with the newer type RED retainer #315232. If your engine has that weird linkage that connects all four of those needle valves, the newer RED retainers will enable you to discard that linkage. The RED retainers make it impossible for the needle valves to vibrate out of adjustment.
(Carburetor Adjustment - 2 Slow Speed Adjustable Needle Valves, each carburetor)
Initial setting is: All (4) Slow speed valves = seat gently, then open 1-1/2 turns.
Facing the carburetors, start with the top left needle valve, then the top right valve, then the bottom let valve, then the bottom right valve. It may be necessary to redo these steps to get the adjustments ideally set
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.
Do not attempt to gradually adjust all four of the valves 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.
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.
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