5hp Sea King problems

I have a 1957 Sea king made by Gale model #GG9002c can anyone tell me how to set the fast and slow knobs it will start and run on fast but will die when I try it on slow. The gas mixture is 24:1 and the carb has been cleaned with new gaskets.Thanks

Standard OMC settings. 1 1/2 turns on the upper (low speed) and 3/4 turn on the lower (high speed). You can adjust the low speed in a barrel or tank. Turn clockwise until the engine sputters noting the position then counter-clockwise until the engine sputters. Best setting will be midway between the two points. Adjust the high speed in the same manner but do it on the lake at wide open throttle (WOT). After setting the high speed you may need to readjust the low speed. There maybe an idle stop on the side of the tiller arm that you can set for a chosen speed.

(Carburetor Adjustments - Two Adjustable N/Vs)
(J. Reeves)

Initial settings are: Bottom high speed = seat gently, then open 1 turn out. Top slow speed = seat gently, then open 1-1/2 turns.

Setting the high and low needle valves properly:

NOTE: For engines that DO NOT have a shift selection, obviously there is no NEUTRAL position. Simply lower the rpms to the lowest setting to obtain the low speed needle valve adjustment.

(High Speed) Start engine (it will run pretty rough), shift into forward gear, take up to full throttle. In segments of 1/8 turn, waiting for the engine to respond between turns, start turning in the bottom high speed needle valve. You'll reach a point whereas the engine will either start to die out or spit back (sounds like a mild backfire). At that point, back out the needle valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest setting.

(Low Speed) Slow the engine down to where it just stays running. Shift into neutral. Again in segments of 1/8 turns, start to turn the top 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. Again, 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 adjustments, 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.