Superjet revs but won't accelerate.

[ejn1214]

I bought a 94 Superjet this summer with no previous experience. Ran great most of the summer, but now I am having an issue. For the most part it runs fine, but when it comes out of the water at all (even a small wake or wave), it stills revs ok or over revs since I'm not going anywhere, but loses power or stops accelerating and comes to an almost complete stop. The engine will still be running, and in a few seconds I can accelerate again. Basically it seems like water isn't flowing through properly. I did have some weeds underneath before this problem started, but I have turned it over and it looks all clear now. Sorry if this doesn't explain it well enough, but I am completely new to this. Anyone have any ideas/suggestions?

Thanks

 

[boostedegos]

Sounds like cavitation. What kind of condition is the impeller in?

 

[ejn1214]

Sounds like cavitation. What kind of condition is the impeller in?

To be honest, I didn't look at it real closely. This seems like a good place to start. Thanks for your input.

 

[X2Kid]

We need images! Remove your intake grate and take an image of the front of the impeller. Next, get somebody to hold a torch in FRONT of the impeller and take an image (without flash) from the exit end of the pump. We want to see what sort of clearance you have between the impeller and its housing, and the condition of the impeller itself.

 

[ejn1214]

So I took the ride plate and the other plastic grating off to get a look at the impeller. Not sure if you can see anything with these pictures. To me, the impeller looked ok. There was one small imperfection, and there is some sand between the impeller and the "tube" (not sure what it is called) that surrounds the impeller. I can take more apart, but I ran out of time today and wasn't sure what I would do with more of it apart anyways. Let me know what you think or if you can even see anything from the pictures.

Thanks Again!

 

[X2Kid]

Image 4 tells the story. That light you can see between the edge of the impeller blades and the tube it resides in (wear ring) is excessive. The gap between these two is allowing cavitation as suggested in post 2.

You will need to have both your impeller and the housing (wear ring) professionally measured by an engineer to determine if either or both items are worn beyond their limits.

An otherwise sound impeller can have the edges of its blades welded and then machined back to the correct diameter. A company like Impros can do this for you. In fact, they can probably effectively recondition it to 'as new' for far less than a new impeller.

The wear ring is usually replaced as a whole unit. A stock Yamaha unit is expensive. Solas make a solid stainless steel replacement. Both SBT and WSM offer budget alternatives. I'd probably source this item from JetManiac and he can sort you out with your budget in mind.

 

[ejn1214]

Thank you. This is extremely helpful. So I see Impros is in CA, and I live in Wisconsin. Do you think there is somewhere around me that would do this sort of thing, or are you suggesting I would have to take off the part and ship it to them to measure and possibly recondition it? Thanks again for helping me out.

 

[jetx]

Before you go crazy and start shipping things away just measure the gap with a feeler gauge and that will tell you whether your in spec or not.

Also check the pump seal they are known spots to leak air...also the midshaft

Usually the impeller wears before the wear ring, and if you have sand in there that could be why you now have an issue, sucked up to much of it.

 

[ejn1214]

Before you go crazy and start shipping things away just measure the gap with a ************ gauge and that will tell you whether your in spec or not.

Also check the pump seal they are known spots to leak air...also the midshaft

Usually the impeller wears before the wear ring, and if you have sand in there that could be why you now have an issue, sucked up to much of it.

I'm still working on this problem. I do not think it's the wear ring or impeller, but you mention the pump seal and midshaft as places to check for leaks. How would I go about checking that and what I be able to fix that problem myself? My dad is rather mechanically inclined, but I'm not sure at this point if I should just take it into a Yamaha dealer. Any opinion on that?

 

[X2Kid]

Please put a feeler gauge between the impeller and wear ring and let us know the clearance. The point where the gap between them is greatest.

 

[DAG]

Wtf why is feel -er gauge a censored word? @SuperJETT

 

[SXIPro]

Wtf why is feel -er gauge a censored word? @SuperJETT

Same reason reach-around gauge is.

 

[X2Kid]

Yet screwdriver is OK?

 

[ejn1214]

Thanks for all the help so far. So I finally think we have something. I am not sure my terminology is correct but here it goes. I think the coupling halves appear to have separated. For clarity, the coupling half with the black isolator is on the midshaft/bearing side. The coupling half without the black isolator is on the engine shaft side. My question is how can the coupling halves be moved back together? Do they slide or move on the shafts? What needs to be loosened in order to put the coupling halves back together. The mid shaft bearing looks like it's in good shape. Thanks again for all the help.

 

[mike b]

Did you loosen your motor and slide it forward or just take the coupler cover (black plastic cover over top these two coupling halves) and take the picture. If you didn't move the motor and just took the picture I don't see how you have been riding the ski like this because the couplers need to be engaged in order to spin the prop. Unless your motor mounts are all broken and the motor slides around freely and when jumping they come back together but this seems far fetched.

Can you move the motor around with out unbolting anything? Yes these two couplers slide together and engage. If you are able to slide the motor either direction, especially to engage the couplers back to normal without unbolting anything then I would assume your motor mounts are all shot.

If you cannot move the motor around (picture looks like motor mounts are in normal position but hard to tell in pictures you have provided so far), then I would look into the midshaft (short shaft with other coupler and black dampener) and see if you can slide that around to line up and engage the couplers together. If you can move this then the midshaft bearings would be gone and spline engagement would be off.

Not sure since ski isn't right in front of me but something is way off on your ski. I haven't seen a working and riding ski with couplers not fully engaged like in those pictures. GOOD LUCK

 

[ejn1214]

I did not loosen the motor and just to make sure it wasn't loose, I just went into my garage and tried to see if it was loose (no movement). We just took the cover off and that's the picture you see. I have very limited technical knowledge, and while my dad is good with cars and is generally good with this type of thing (electrical engineer), this is our first experience with a pwc. So thanks for being so helpful and not condescending. BTW I just bought it last year and it was running perfect before this started to happen. I put it in the water a week ago and it had trouble starting but eventually did, ran ok for 20 seconds before the same issue. I never got it to accelerate again before I got it back to the dock, so maybe the problem was exasperated.

 

[Bayerj]

The midshaft slid back, it can move in the bearings it's sitting in. Gotta move it back forward, probably have to pull motor, pull midshaft, and use a press to get it back into spec, there is a thread on here that specifies the measurement

 

[smoofers]

The midshaft slid back, it can move in the bearings it's sitting in. Gotta move it back forward, probably have to pull motor, pull midshaft, and use a press to get it back into spec, there is a thread on here that specifies the measurement

This. You'll have to unbolt the motor and slide it forward at a minimum to pull the midshaft. Might as well just pull the motor. The pic below is straight from the service manual (I added the highlight). The "a" distance is the side that faces the jet pump.

 

[mike b]

Yeah if motor isn't loose and this happen I would guess midshaft bearing is toast or you had very weak engagement/alignment. Loosen motor, slide forward or removed and inspect midshaft to see if you can move it by hand. It should spin, but it shouldn't pull/push lengthwise.

Still not sure how midshaft would slide that much tho. If you had good spline engagement with driveshaft you wouldn't have a midshaft sliding around. I would inspect the splines. If your midshaft is moving up and back like it should not be you might have stripped splines. Bearing housing is cheap so I hope it's just that but inspect it all while you are in there.

 

[ejn1214]

So I planned to remove midshaft to see if it had slipped through the midshaft bearing at the hull exit. This seems like this would be a fairly time consuming task, and if removing it, I would perhaps just replace the midshaft bearing itself. Since we would probably replace the mid bearing any way, I decided to try to use 2 clamps to force the coupling halves together, and see where the slippage would be. I marked the midshaft side with magic marker, on the shaft to rear coupling half, and midshaft to midshaft bearing, t see where the slippage is occurring. I clamped the coupling halves together, and coupling halves came back to normal position. Marks on rear coupling half shaft looked like they did not slip. (Could still see the markings on the shaft.) I estimate the coupling halves moved together a distance of about 0.75 to 1" to become fully engaged.) At full separation, it probably moves 1 inch. By the way, the midshaft bearing to hull seal looked fine.

I did a test run. During first acceleration, had same issue almost immediately. Previously I could restart and go ok for a bit so the separation must be worse now. I viewed the midshaft coupling, and the coupling halves were separated again. It appears that the front half coupling must have moved forward on the engine shaft, or the engine shaft moved forward, in engine bearing. (Doubtful that the engine bearing allowed slippage)
I tried to determine where the movement was coming from. (Midshaft to bearing slippage, Rear coupling have to midshaft slippage, Forward coupling half to engine shaft slippage, engine shaft slippage. I looked at tge coupling halves and did not see a key way, nor set screw. I am wondering how the coupling is secured to shaft (Press fit / interference fit)?

So my questions are:
1. In general, how to solve the problem of the coupling halve/s moving and separating?
2. Assuming the front coupling half is moving (With respect to rear coupling) how is the front half coupling secured to the engine shaft. Key way? Spine Shaft? If key way, is there a set screw? How do I correct the situation, where the half coupling is apparently sliding on the engine shaft?. Also, the engine mounts seem proper, and there is no sign that the engine has shifted.

I included a picture of the couplings with clamps and then a picture of the couplings after riding it and getting the separation again. Thanks again for all the help.