71 Johnson 50HP will not run well in water

I have a 1971 Johnson 50HP that was given to me on a 14' boat. It hasnt run in a few years, the previous owner had the same problem that Im having. Its runs great on muffs, as soon as it hits water the idle drops drastically. It will not idle unless the the lever is in the start position, and is very hard starting. When Im on the throttle on the lake it sounds ok but will not get close to full speed or RPMS and uses a lot more gas than I think it should. 5 gallons in about an 8 mile run. It has good compression, 125 psi both cylinders. I have cleaned and rebuilt the carbs (twice), just to make sure I didnt miss anything the first time. The reeds appear to be OK. Changed the head gasket, fuel line and coils, and de-carbed once. It does not overheat. I have a lot of 2 stroke experience with motorcycles but not boats. The owner of a local marina has suggested possibly the stator. Im at my wits end, any suggestions would be helpful. I have a service manual, the carb linkage and timing seems to be correct.

Re: 71 Johnson 50HP will not run well in water

They will always idle faster on muffs, no backpressure on the exhaust.
Idle should be set with boat in the water or engine in test tank, I think 650-700 IN GEAR should be about right.
Make sure that you don't have any external fuel leaks, carb float settings are correct. Check the high speed jets to make sure they are the proper ones for your engine.

Re: 71 Johnson 50HP will not run well in water

Thanks Daviet,

The problem is it wont idle at all in water, once I get it in the water it stalls and wont start, I could only start it by bypassing the neutral switch with about half throttle. On land, no problem with muffs. Has a new fuel tank and hose, float settings seem to be correct. Float is level when carbs are upside down, and 3/4" when hanging. Any ideas on the stator?

Re: 71 Johnson 50HP will not run well in water

What I am trying to say is that if the idle is to low, it will not run in the water. The backpressure in the exhaust system will not allow fuel mixture into the cylinders.
It might run great on muffs because of no backpressure, set the idle at about 1000 RPM on muffs and reset the idle when in the water, probably about 650-700 IN GEAR, IN THE WATER.

Re: 71 Johnson 50HP will not run well in water

Thanks Daviet,

Ill try to set the idle in the water, its just very eratic in the water, its set to 1000 - 1100 rpms on muffs , i drop it in the water and it wont run , Im waiting for an intake gasket (checked the reeds) , should be here tomorrow, let you know how it goes. Thanks for the help.