TOPIC: Johnson 1959 5.5HP

Motor will start and run at high RPM (3,000 to 3,500) when I back it down to about 900 RPM it stalls. The carburetor has been cleaned and rebuilt, compression is 95lbs on each cylinder, points are new and set at .020, spark plugs are set at .030, the spark is good on each cylinder. Any help on why it won’t idle ?
Bob

This may get more responses in J,E,G,O, forum.
Anyway. am assuming the engine is running on the double line fuel tank. Do yourself a favor and pump the button on the tank when you idle it down and see if that helps the engine stay running. How about pulling the choke momentarily? Please do these and report back.
Were new parts used in the carb rebuild? if so were the parts OEM or aftermarket? OEM will provide new packings for the high and low speed needles to keep them from sucking air around the needle shafts.

Does changing the idle mixture setting have any effect on how it runs? They can be a bit sensitive to adjustments.

If no change no matter how you turn the idle mixture needle, your idle circuit may still be plugged. The idle circuit draws fuel from a passage that goes up the side of the float bowl. If that passage is blocked, the hole in the float gasket swelled-shut (very common to see that), or some other issue, it won't pull fuel up into the idle circuit. The cork or later-style rubber washer has to be there between the carb body and the float bowl, to properly seal off the fuel passage so fuel can flow up into the main jet and emulsion tube.

Another issue that can cause poor operation on these older twins is cracked coils. If the coils are original and have any cracks in them, they're shot. Later replacement green, blue, or black coils usually work much better and don't seem to have the problem of the older-style clear-insulated coils.

Thanks, I’ll open the carburetor and check the idle circuit. Coils,points, condenser are all new good spark on each plug.
Thanks for the information
Bob