strange cavitation issue sportster 150

[Johnny63]

I bought a sportster 150 215scic last year and the performance was ok at best. i usually do a tear down and inspection of the driveline at the end of the season so I figured I would find some issues. First major issue was this boat had obviously sat for long periods of time in salt water. The reverse bucket bracket was corroded to the venturi nozzle and jet pump assembly. Finally after getting all that out I noticed the jet pump house was full of holes around the perimeter caused by corrosion. So I replaced everything with new parts which included:
bellows with bearings
carbon seal , hat and bellows
driveshaft
jet pump assembly
venturi
reverse bracket and bucket
impeller ( solas 14/19)

The boat struggles to get on plane, i swapped out the neoprene seal for a riva one thinking that might help, no luck. if I can get on plane it rides fine. the entire driveline is new. i cant figure it out, i had it apart multiple times looking for anything. I'm totally stumped.

 

[MacSeaDoo]

Check the alignment of the pump bucket in forward. It should be clear out of the pump flow. If it is in the flow it greatly affects getting on plane but becomes less so as you are on plane.

Just a thought.

FYI here is a photo of my 150 pump in forward position.

 

[POPPS]

Pic is dark,,,when you say the housing is full of holes,,,can you post that pic?

 

[Johnny63]

Pic is dark,,,when you say the housing is full of holes,,,can you post that pic?

I no longer have the old pump housing, it was almost corroded in half around the perimeter

 

[MacSeaDoo]

Curious on how you made out?

 

[Johnny63]

Still have the issues, replaced wear ring again and put in new OEM impeller. One thing I did notice was that the stainless hat was off center from the carbon seal. My next step is to try an engine alignment, and new carbon seal. The bore of the seal is not touching the shaft but it is off center by at least 1/8 inch. I had the boat out yesterday and was able to get on plane by catching other boats wakes or by steering back and forth as i accelerated essentially doing a tight S pattern. Once on plane it was a rocket.

 

[MacSeaDoo]

Do you have a photo of the carbon seal and alignment?

What happens when you try to get on plane? Just a ton of cavitation?

If you do have cavitation, anything that can introduce turbulence to the water stream will cause this.

1..check the grate and ride plate to make sure they are properly sealed as if they are not, they will allow the feed of water from areas outside the normal stream. A simple test here would be to seal all the seams with ducktape and see if that changes it. This would be the seams around the grate and ride plate.

2.. you mention the bucket was so corroded. What does the grate look like?

3.. if you did have a misaligned shift, your carbon seal will not sit right and can be a place of air being drawn into the the water stream on the suction side of the pump. Any air will be catastrophic to the laminar flow of the water, basically causing cavitation.

Does the carbon seal leak?. Because if it does leak water in large amounts, it will most likely introduce air from the hull.

Here, just put the boat on the trailer and fill the hull with water. Watch for it leaking under the grate.

 

[Johnny63]

thanks for the reply.

1. the ride plate and grate are both sealed good

2. the grate is in excellent condition

3. see picture this looks like an indication something is off. also looing from the back with the pump off i noticed seeing more of the hat on the starboard side.

4. the carbon seal does not leak water into the hull, very minimum if at all. ( i did not do your water test, this is merely from monitoring the engine bay while at the lake in operation and while floating )

 

[Johnny63]

ok so I did an engine alignment, went over everything thoroughly again. in testing the boat I was able to get on plane easily by starting out and then making a hairpin turn to the right. I would be on plane but facing 180 degrees from my starting direction. at low speeds it feels like I am riding on severely underinflated tires.

 

[Ajent]

ok so I did an engine alignment, went over everything thoroughly again. in testing the boat I was able to get on plane easily by starting out and then making a hairpin turn to the right. I would be on plane but facing 180 degrees from my starting direction. at low speeds it feels like I am riding on severely underinflated tires.

When you're trying to get on plane, what are your rpms doing? Flying up to the rev limiter or staying low?

 

[Johnny63]

When you're trying to get on plane, what are your rpms doing? Flying up to the rev limiter or staying low?

Shoot up to rev limiter.

 

[spinyard]

put some heavy duty zipties around the driveshaft bellows boot right behind the carbon seal, the thrust is pushing it back allowing air in there, causing your cavitation, the idea it to put more tension on that bellows boot

 

[Johnny63]

put some heavy duty zipties around the driveshaft bellows boot right behind the carbon seal, the thrust is pushing it back allowing air in there, causing your cavitation, the idea it to put more tension on that bellows boot

I will try that tomorrow and report back.

 

[MacSeaDoo]

If the alignment is off, it will round out the shaft side of the carbon seal.

Do you have a go pro?

When I was searching for the source of my water leak, I zip tied a flat led flashlight to a stick with my go pro and took video while underway.

It quickly pointed out my problem, which was not the carbon seal.

 

[Johnny63]

If the alignment is off, it will round out the shaft side of the carbon seal.

Do you have a go pro?

When I was searching for the source of my water leak, I zip tied a flat led flashlight to a stick with my go pro and took video while underway.

It quickly pointed out my problem, which was not the carbon seal.

A week ago I had it all apart again, carbon seal looked mint. The shaft is not hitting the inner diameter of the seal. Last weekend while testing on the lake the bilge never came in. Went home and filled water in the bilge with a hose and it kicked on so I know it works.

Unfortunately I do not have a GoPro but I have thought about coming up with a way to see under the boat when all this is going on.

 

[slimbobaggins]

Did you ever find the source of your cavitation?

 

[Johnny63]

Did you ever find the source of your cavitation?

not even close, I'm ready to just give up. never had a situation like this before ever.

 

[POPPS]

The drive shaft does not appear to be centered?

 

[Johnny63]

The drive shaft does not appear to be centered?

It is more important that the engine and pump are aligned.

 

[Srt]

I have a Sportster 4tec with cavitation problems as well. I can get it on plane and moving fast if I ease it up slowly, but if I hammer the throttle before it's on plane, it just cavitates.

Did you make any progress on figuring out your problem?

 

[Johnny63]

I have a Sportster 4tec with cavitation problems as well. I can get it on plane and moving fast if I ease it up slowly, but if I hammer the throttle before it's on plane, it just cavitates.

Did you make any progress on figuring out your proble

I did not . Unless i can physically see something I can not test until spring.

 

[TheDirtyBrit]

Did you try the zip tie trick around the bellows? I had a bad cavitation issue on my 180 and I put a fat zip tie (as suggested above) around the narrow part of the bellow (it basically spreads the bellow out more and puts a bit more pressure forward onto the carbon seal). I found it made a big difference. Now I know I need to replace the bellow/carbon seal when I get time. The idea behind it is that as the bellow gets old, it loses its spring and allows the carbon seal to ever so slightly pull back from the metal mating surface when you throttle up. It really doesn’t take much air to ruin the pump performance.

 

[Johnny63]

Did you try the zip tie trick around the bellows? I had a bad cavitation issue on my 180 and I put a fat zip tie (as suggested above) around the narrow part of the bellow (it basically spreads the bellow out more and puts a bit more pressure forward onto the carbon seal). I found it made a big difference. Now I know I need to replace the bellow/carbon seal when I get time. The idea behind it is that as the bellow gets old, it loses its spring and allows the carbon seal to ever so slightly pull back from the metal mating surface when you throttle up. It really doesn’t take much air to ruin the pump performance.

Tried that, I work in HVAC and used the large zip ties used for attaching flexible duct, no change.

 

[TheDirtyBrit]

Oh okay. One more thing, Is the rubber spacer/bung attached to the end of the driveshaft going into the engine? If it’s missing, it could cause the shaft to move forward slightly and break the seal? just throwing stuff out to maybe help!!

 

[Johnny63]

Oh okay. One more thing, Is the rubber spacer/bung attached to the end of the driveshaft going into the engine? If it’s missing, it could cause the shaft to move forward slightly and break the seal? just throwing stuff out to maybe help!!

the bumper is there, i'm wondering though if the engine needs to be slid aft somewhat. i cant find a spec anywhere as far as front to back positioning of the engine. could be a mount issue, still lost at this point.