3 hp 2 stroke misses mid range

[happy hour iv]

Tohatsu 3 hp 2 stroke on my inflatable. Starts fine, idles fine and runs good above 75 % throttle. Mid range has a very distinct miss. I suspect a rich mixture issue since good operation other than mid range precludes ignition. Carb has idle speed screw only. Disassembled gives a metering jet option but i suspect this would affect higher throttle also. The only other adjustment is for the float. Does anyone have some input on this?

 

[pvanv]

Nope. That is incorrect. No such motor ever made. What is your actual model? If M3.5, you can adjust the slide valve to any of 3 or 4 different slots in the pin to adjust richness. Look at the plug color to determine whether too lean or too rich.

 

[happy hour iv]

Model is M3.5 but i believe it is rated 3 hp. If it runs smooth at higher throttle am i risking a lean mid range by adjusting ?

 

[pvanv]

The 3.5A has the water pump on the prop shaft, and starts in gear... no neutral. The 3.5B has it on the drive shaft, and has F-N-R. They were available as a 2.5 or a 3.5... never a 3. Both use a slide type carburetor. Assuming oil mix is correct, and ignition is good, then checking plug color will tell whether rich or lean. Then adjust accordingly. When I send these to Denver, I lean them out one notch. They seldom need adjustment otherwise. If the carb won't come clean enough with ordinary cleaning, some folks set them one notch rich. I try to avoid that, because future cleanings might then make it too rich. These things are nearly indestructible, so after verifying oil mix, ignition and plug color, adjust as needed.

 

[happy hour iv]

Paul, thanks for the ideas. Got me thinking how old the motor is with a carb that has never been removed let alone cleaned. Ordered the kit and will see what that does then if needed will adjust slide valve. As a note, the Tohatsu factory repair manual lists carb disassembly instructions for 2.2-3.0 and slightly different instructions for 2.5-3.3

 

[pvanv]

Remember not to just install the kit, but clean the carb correctly. That motor was only available as a 2.5 (smaller carb) or 3.5 (not detuned with smaller carb). There never was a 2.2 nor 3.0 nor 3.3.