Fuel Problem?

[Jtgator]

I just bought a 21 ft pontoon boat with a 1996 Merc. 2 stroke 90 hp o.b.
It runs fine except it seems to lack speed. Took it to my mechanic and he said a short fuel hose at the carb was kinked and he changed the hose.
Still have problem. With the throttle wide open only do 15mph on speedo, rpms at 40K. The engine does not sound like it is even straining, like it could still rev higher if it had more fuel. Im thinking the throttle cable maybe stretched and is not opening the carbs fully. With the engine off and the helm throttle fully forward I checked the engine linkage and I can advance the throttle more manually. Compression 135 psi all around. I know pontoons arent meant for speed but this is slower than my last pontoon boat with a 70hp.
Any thoughts?

 

[Faztbullet]

Re: Fuel Problem?

Check the basics, spark, compression and fuel delivery. It may have a cylinder down on compression if it had a kinked hose as you where told as this would make that cylinder run lean. It also could have dropped a cylinder do to a electrical problem(switchbox, coil, wiring issue)

 

[jerryjerry05]

Re: Fuel Problem?

Look for soft hoses.Is there a quick disconect in the line? They go bad and suck air.Check the bowls for gunk.Rebuild the fuel pump.
Then the prop.Your motor should do about 5500rpm at WOT.
If your overpropped then your motor won't rev up.You have a spare?
Some dealers have spares setting around.They loan them so you can test and buy the right one.
What prop?
Check these things and post your results.J

 

[CharlieB]

Re: Fuel Problem?

All troubleshooting is recommended to begin with the basics, verifying the compression and testing for adequate spark, to ensure the motor is mechanically able to perform.

Next is cleaning carbs, then adjusting the carbs, synchronizing the throttle openings/closing at idle and WOT, adjusting timing at WOT. Commonly referred to as 'Linking and Synching'.

Final adjustment of idle mixture and idle speed is done ON the water while IN gear.

Only after all this is done should you begin to question prop size/pitch to adjust WOT RPM.

Start with the basics and it will save you unnecessary parts, time, and money.