1996 Yamaha 4 HP boat gas engine -- the idle circuit works fine .
When I attempt to rev it slightly and simultaneously engage it into gear (after it has warmed up ) , the engine dies . If I were to rev it w/o putting it in gear , it seems fine .
Additionally , if I rev the engine while the choke is halfway on , the engine will continue to run , but lacks full power . As I remove the choke to permit full air flow , the engine sputters and dies .
Is this a high speed carburetor circuit fuel pathway issue ? It is my guess that the extra load on the engine when it is put into gear , will stress the carburetor high speed circuit pathway and the carb can not deliver enough fuel .
What is the diagnosis / solution ? Is a fuel system cleaner appropriate for this gas/oil mix 2 cycle engine ?

 

I think you are right about the high speed jet on the carb. The engine will run fine with out a load, but if it is loaded the carb can't deliver enough fuel, so it leans out and dies. Partially choking the carb will cause it to suck more fuel, so it will try to run. You may also check to see if enough fuel is getting to the carb to begin with, dirty filter etc, this will cause the carb to starve for fuel as you load the engine and cause the same thing. I would not advise you to use any fuel treatments in a 2 stroke motor, anything strong enough to clean out the gunk is strong enough to break down the oil in the cylinder that is carried with the gas. I recall reading a warning about ethenol mixed gas used in 2 strokes, the alchohol tends to clean out the oil causing engine damage. I don't use that stuff either.

 

I agree. Do Not use any system cleaning additives in your 2 stroke engine. The only proper way to correct your problem is to remove and disassemble your carb, and clean it out....if there is in fact an obstruction. Have you backed out the air/fuel mixture screw(s) a little? Do you have sufficient fuel pressure to the carb?