The fact that it revs up in neutral does't mean anything. If it runs it will rev up with no load even if 1 cylinder of a multicylinder engine isn't working. Does this engine have 1 cylinder or more than 1? One carb or more than one? Try pumping the fuel bulb when it starts to sputter. If it picks up and runs better you probably need to rebuild the fuel pump (not difficult). Make sure the tank vent is open, remove the gas cap if necessary to be sure. Check for fuel/air leaks at the hoses and all connections, especially where the fuel line attaches to the tank or engine. Try manually choking it when it starts to sputter. If it picks up its running lean, most likely from gum and crud in the carbs, requiring a COMPLETE clean and rebuild. Remove the engine cover and airbox on the carb if it has one and observe the carb when it acts up. Is the choke flopping around or any linkages loose and acting up? Does it look like gas is leaking out of the carbs (stuck open float valve)? When you pump the fuel bulb, does it eventually get firm? It should, if it doesn't and/or gas leaks out of the carb when you pump it the float valve is stuck open (gum).
Shut the engine off while it is actin up and remove the spark plug(s) and examine it(them). Black sooty= rich, brown=good, gray/white= lean.
It is also possible that you could have ignition problems but my first thoughts are any of the above.
Once somebody tells you the year, get a manual- your best investment. If and when you rebuild the carbs, remove them, dismantle them, remove non metallic parts, soak overnite in carb solvent, blow out with compressed air, and install rebuild kit parts with all new gaskets. Don't reuse gaskets, it just confuses the issue when you are trying to nail down problems. Spraying a little bit of carb cleaner on the surface of a carb just makes it look pretty. Good luck and keep us posted.
mariner 5hp not running right in gear
Linear Mode
