2008 8hp high thrust 4 stroke

[Ceedeeoutdoors]

Motor is tough to start Motor idles rough and quits. It will rev up to high rpms in neutral but in gear under load it only gets to about half rpms at full throttle. And will occasionally " backfire out the silencer. Timing settings are correct according to the manual Plugs are new, plug coil is New, fuel pump is New and i bought a new carb after cleaning the other one several times with no improvement. Plugs are gap to spec. Top cylinder compersion is 148, bottom cylinder is 153. This motor shares a fuel tank with the big motor. Big motor runs fine. New fuel lines to the smaller motor, only thing not changed is the fuel connector on the motor. Any suggestions what could be wrong

[DennisG01]

It shares a fuel tank... but it does it share the same pickup? If not, the ASV could be gummed up. Even it shares an ASV, the little guy may not have enough suction to counter the gum/clog.

Fuel filters?

Connect a portable tank DIRECTLY to the little engine - directly to the pump. See what happens. This will immediately tell if the issue is at the engine or on the boat side, thereby eliminating a lot of guessing and/or replacing things for no reason.

[99yam40]

how do you know the timing is correct?
Have you checked spark timing with a timing light.
to backfire thru the silencer, spark has to fire while an intake valve it open
possibly stuck valve, cam timing or spark timing off