Honda 4 stroke outboard
I have a 9.9 hp Yamaha approx. 2 years old now, and i had a similar problem last season.
One plug was fouled( don''t remember which one) and when testing(this winter,at home) at had almost no water exiting the engine as well.
Thru last season it seemed that whenever i had to enter and dock at the busiest locks it stalled when needed but only when shifting from FWD to REV.
I cleaned all cooling tubes( whitout taking the engine apart)and flushed with water thru adapter at the bottom (near prop).
Adjusted valve timing,they were all to wide.
Renewed plugs and oil and had a testrun.
Now runs like a swiss watch, without stalling( 2 months now)I''m still wondering if it was the baby-clams(fresh water) fouling the tubing,or bad plugs or a combination, but I think I''ve tackled my problem.
Marc, The Netherlands