1994 Yamaha 4hp 2-stroke tuning.

[jdholt41]

After rebuilding carb and replacing spark plug, engine will only run at lowest throttle setting. As soon as the throttle is advance (idling or in gear) the engine begins to die
and will die if the throttle is further advanced. Problem gets worse as the engine warms up. Would appreciated help.

 

[Sea Rider]

Welcome to Iboats,

Was the motor running properly, strong before the carb's rebuilt to start with ?

Happy Boating​

 

[jdholt41]

Welcome to Iboats,

Was the motor running properly, strong before the carb's rebuilt to start with ?

Happy Boating​

Thanks for responding. No, it wasn't running very well. Sorry, I don't remember why I rebuilt the carb. Was several years ago. Motor not used until a couple of days ago. Runs fine at lowest throttle.

 

[99yam40]

a motor that has set up for long periods of time usually end up with carb problems.
hard to drain all fuel out of carbs, pump, and lines so when the fuel evaporates it leaves residue that plugs things up.

my guess would be carb needs proper cleaning and setting

 

[jdholt41]

a motor that has set up for long periods of time usually end up with carb problems.
hard to drain all fuel out of carbs, pump, and lines so when the fuel evaporates it leaves residue that plugs things up.

my guess would be carb needs proper cleaning and setting

Thank you for your response. When I rebuilt the carb I drained all of the fuel from the engine. Easy to do with this small engine. So the engine sat for 3 years but without a drop of fuel in it. I think your last suggestion is most likely the problem - the three screws in the fuel system need adjusting. I only know what one of them does - the idle speed adjustment. I could not find any info about the other two, although I am sure that one of them is the air/fuel ratio adjuster. I will just have to play with these adjusters. I haven't been able to find a service manual online for this engine.