I have a single pot 2-stroke 4hp Mariner (Mercury). The idle, slow running and WOT are perfect but in the middle of the rev range with a constant throttle setting, it stutters, slows down by (I'd guess) 100rpm, then gradually speeds up to the original revs, only then to stutter and repeat the symptom ad infinitum. My first thought was spark plug, but putting a new one in (BH7S-10 as per manual) has made it only marginally better. The spark plug that came out was pretty clean. The motor (although mid 90s) has had almost no use.
Can anyone please suggest the next thing to look at? Thanks in advance.
Can anyone please suggest the next thing to look at? Thanks in advance.