SOLVED: port motor not revving out ('95 speedster)

[shrug]

i got this boat in march, all four carbs were properly rebuilt + standard tune up. other than the port motor never revving above 4k, both motors run and sound great. the boat accelerates very nicely from no-wake speed. also, while the speedo says im barely hitting 40mph (with only me in the boat, not even 35 with one passenger), i keep up with most of the skis out on the river, so that may just be a speedo inaccuracy (correct me if im wrong, but i believe i read the factory top speed is about 50mph). the only annoyance (other than leaving power on the table) is having to constantly countersteer starboard at WOT.

ive swapped the plugs multiple times and checked the throttle. id consider it being an issue with the motor itself, but this is a relatively new SBT motor (not sure how new), while the SB side is factory and fully revs. when i first got the boat, the factory SB was in need of some TLC, but the SBT motor on the port side ran like a champ.

the dirtbike/atv side of me is screaming high speed screw adjustment, but from what ive learned about jet boats, i believe its a drive issue. if it was a wear ring, the motor would still rev, it just wouldnt provide much thrust, correct?

therefore, my guess would be the impeller, or maybe the pump itself? has anyone faced and solved this specific issue? lmk if any more info is needed. thanks much!

 

[mikidymac]

Is the engine not reaching full rpm or is the engine going full rpm and just not moving the boat.

A pump issue will be like the clutch slipping on a car or motorcycle, the engine will rev to full rpm but the boat willl not go any faster.

If the engine will not rev to full rpm then it's an engine issue.

 

[shrug]

the motor will not reach full RPM. the 4K that i am getting out of it is definitely providing thrust. i was experimenting with every throttle position possible, and one time the port shot up to 6K+, felt like a small shot of nitrous, then dropped back down to 4K. i couldnt replicate that again no matter how i tried.

so since i have freshly rebuilt carbs, would you try giving the high speed screw a little twist?

or would you start with checking for fuel starvation? i have fresh filters but still factory selectors. this boat never saw ethanol fuel, but i would guess that doesnt rule out the selectors. however i would think with a fuel starvation issue it would cut out and/or sputter at WOT, which isnt the case. its almost like the redline has been set at 4K.

 

[mikidymac]

What carb kits did you use to rebuild the carbs?

Yes, new selectors no matter what.

 

[shrug]

all mikuni parts on the carbs, and they were done by my local pwc shop (i bought all the parts, he just finished the rebuilds). im confident they were done correctly.

as i said, if it was starving for fuel, wouldnt it sputter and cut out at 4K+ RPM. its of course not like a diesel where the amount of fuel determines revs.


now, does this sound more like a fuel starvation issue or a high speed screw adjustment?

 

[mikidymac]

Fuel starvation.

On a stock seadoo it will run perfect with the stock settings. If your's does not you have something else wrong.

 

[shrug]

hmm okay ill try and figure out a way to diagnose that, and in the meantime swap out the selector switch.

 

[JeremyD615]

The selector switches are a pain on this boat, so replace them, don’t attempt to clean them... You have to remove the throttle quadrant to get to them, and it takes some hand contortions to get them out. I have a feeling that this is your issue though.

 

[shrug]

hmm that just goes against everything i know about two strokes but as ive noticed its an entirely different aminal on the water. okay ill order a couple and in the meantime bypass the one with a union and see how it goes.

 

[shrug]

after about three minutes of WOT on the river sunday, the port motor starting revving higher and higher, then cut out all together and refuse to restart, other than on fluid. pulled the plugs, and this time they had a story to tell. one plug looks healthy while one was looking a little lean, so thats gotta be an issue with the carbs.

 

[mikidymac]

Might want to check compression.

 

[shrug]

yeah so that didnt solve it.

its an ignition/weak spark issue. i put fresh plugs in it and took it out last weekend. checked the plugs and mag plug looked healthy while pto plug was wet but looked barely fired. i shouldve swapped wires while in the water.

lol issues that only present themselves under load are annoying on boats if you dont live on the water...

so im going to head out now and start going through the ignition system. lmk if you have any tips/tricks.

 

[shrug]

SOLVED: i took the engine cover and intake/flame arrester off. we hit the water and noticed the clear fuel line between carbs didnt look like it was supplying enough pressure. also we could clearly see fuel spraying down the venturi on the MAG carb but not the PTO. i had my friend partially choke the PTO carb with his hand and it rocketed up to around 6k.

somehow the high speed jet was completely clogged on the PTO carb.

a thank you to Dr Honda: i came across your thread on how even pros get things wrong sometimes. i had these professionally rebuilt cause i was on a time crunch and knew next to nothing about these craft at the time. i cleaned the fuel system out well before reinstalling them and this issue happened right off the bat, not like it was fine at first. after reading that i changed my suspicions back to fuel from ignition.

and a thank you to miki, jeremy, and everyone else who seemed positive it was fuel starvation.

im just happy to have a properly running craft, while also learning something.

 

[JeremyD615]

I know it’s super frustrating to have to go back into something that you just rebuilt or replaced, but I’ve learned that you just have to follow the symptoms on these things, even if it’s something you just checked... I’m glad to hear you got it sorted!