5hp Tohatsu stalling in gear

[Hackers]

Have a 5hp 2014 4 stroke tohatsu that i'm having problems with. It stalls when going into gear. I have many outboards and parts so here's what i've tried so far. New carb and new fuel pump, still same issue, changed oil (actually used a few different levels), new fuel connector and complete new fuel hose in system and spark plugs.
Any help would be great as should be an easy fix but struggling, many thanks.

 

[pvanv]

Year is irrelevant; model is important. I assume you have an MFS5C. The 4/5/6 are identical, except for the carburetor. Idle speed is critical, due to the low moving mass of the small, 1-cylinder motor. What is the idle RPM in gear and in neutral?

Run 10w-30 non synthetic oil, and keep it between the hash marks on the dipstick. Screw the stick in to check level.