No thrust -2000 Sportster

[1970_mgb]

Hi , need some help with this boat.
After top end rebuild, engine seemed to run fine but had low thrust so couldnt even plane out.
Had pump completely rebuilt by a shop including drive shaft carbon seal wear ring and impeller. It was checked out late last fall by mechanic who said it ran great.
This spring took it out and same problem. No thrust. Max speed 9 mph.
Can not hear any sign of cavitation (high revving) and not taking on any water. Engine runs smoothly and starts easily. Unfortunately tach is not working so not sure about rpm.
One thing i notice that after about 75 percent throttle engine does not respond by further increasing revs. I checked the throttle butterflies and they are fully opening. Compression is 138/140. New plugs.

Any thoughts would be greatly appreciated. Not sure what to check next.

 

[splishy]

If there's any way to swap out the tach so you can get an idea on RPM's that'd be a good start. Have you also checked for a faulty neutral switch as that can cap RPM's to 3.5k? Hopefully it's that easy!

 

[1970_mgb]

The neutral switch thing I was not aware of. Ill check it out. Maybe it can be bypassed temporarily?

 

[splishy]

The neutral switch thing I was not aware of. Ill check it out. Maybe it can be bypassed temporarily?

Yeah, look in the sticky MPEM troubleshooting guide on here. The switch is naturally open so you should be able to bypass it by unplugging it.

 

[1970_mgb]

So I got the tach working and took boat out again. So with only myself aboard it hit 35 mph by gps at 6800 rpm. Then with 2 aboard it only made 9 mph at 7100 rpm.
Engine is running great . No missing and starts easy.
I know what cavitation sounds like and it doesnt seem like that and its not hitting any rpm limit but at 7100 rpm and poor thrust its got to be something in the jet pump No?
Maybe wrong impeller or wear ring got put in at some point??
Im at a loss right now

 

[mikidymac]

If you are getting 7,000 rpm and no thrust is has to be the driveshaft splines are stripped, impeller is bad, driveshaft seal is bad or wear-ring is bad.
Has to be pump or driveline.

 

[1970_mgb]

If you are getting 7,000 rpm and no thrust is has to be the driveshaft splines are stripped, impeller is bad, driveshaft seal is bad or wear-ring is bad.
Has to be pump or driveline.

Thanks. The guy who rebuilt the pump and driveline told me today that a very small amount of damage or debris in the wear ring can cause this. We will see. There is nothing obvious to me.
Would a bad seal mean water in hull cause there is none.?
Im thinking a stripped spline would make a lot of noise.

 

[Stevie96xp]

You it has to be something in the pump pull it and see what you see cause you motor is recent out and your not going anywhere it’s something In your pump

 

[1970_mgb]

It was the pump.Looks like something hard went tbrough the impeller and chewed up wear ring and damaged blades. Incredible must have happened on first launch after rebuild.

 

[Stevie96xp]

Yep that would do it