impeller has 1/8" rotational slop, please advise.

[Project101]

wifes 650 sx has rotational slop on the impeller, up and down is tight but rotational is 1/8" shes been riding that way for about 8hrs.
has anyone had this happen before?
if so was it in the prop or the driveshaft or both. i won't be home for a month so I'm trying to order parts so I can knock it out when I get home and we can ride.
any info would be great.

Thanks

 

[Harbor]

Are you sure the slop is not from the driveshaft and mid shaft splines ?

Hows the coupler rubber ?

My wife’s SX rattled a lot at idle on the work stand, I assume it was from slop in the mid shaft and driveshaft splines. but worked fine And still does after many years

I never tried rotating the driveshaft to check slop though

 

[Project101]

Are you sure the slop is not from the driveshaft and mid shaft splines ?

Hows the coupler rubber ?

My wife’s SX rattled a lot at idle on the work stand, I assume it was from slop in the mid shaft and driveshaft splines. but worked fine And still does after many years

I never tried rotating the driveshaft to check slop though

Yeah it’s definitely the shaft or impeller splines or a combo of both .If I twist the drive shaft and hold the impeller it rotates. And 1/8” inch , it’s def rotational slop. And that funny cuz it’s my wife’s ski aswell and what made me check was how rattly it was on the stand. She has put at least 8hrs on it and it seems fine. But I need that thing to keep running! So we can have “good bonding” so she rides her ski not mine lol.

 

[kevbo]

All 650s had short splines and the seals weren't as good, they tend to wear fast after the grease is washed out. Run it until the splines strip, it will probably go a long time. If you want to fix it right, have a 750 impeller machined to fit a 650 pump and use a 750 ss/xi driveshaft. Its rare to find bad 750 shafts where its impossible to find good 650 shafts.

 

[Project101]

so is it the shaft or impeller spines?

 

[Project101]

*splines*

 

[wmazz]

I wouldn't worry about it. Some impellers make more noise than others. The
o-ring or boot will reduce the noise, but on many old Skat Trak impeller people
have left the o-ring out.

Does it have the stock aluminum impeller?


Bill M.

All brands have their own distinct drive line sound. What kind of maintenance
have you done in the past?

 

[Project101]

I wouldn't worry about it. Some impellers make more noise than others. The
o-ring or boot will reduce the noise, but on many old Skat Trak impeller people
have left the o-ring out.

Does it have the stock aluminum impeller?


Bill M.

All brands have their own distinct drive line sound. What kind of maintenance
have you done in the past?

It has a skat 6

 

[kevbo]

Both splines wear. The problem was a combination of Skats use of a loose fitting O-ring for a seal and the owners failure to maintain clean/lubed splines. Solas had much better seals and would last forever provided everything was installed properly.

 

[Project101]

It has a skat 6

I have done no manitince on this ski I got it for my wife about 8hrs of use ago

I wouldn't worry about it. Some impellers make more noise than others. The
o-ring or boot will reduce the noise, but on many old Skat Trak impeller people
have left the o-ring out.

Does it have the stock aluminum impeller?


Bill M.

All brands have their own distinct drive line sound. What kind of maintenance
have you done in the past?

I have not done any maintenance on this ski so far. Got it for my wife about 8hours of use ago.

 

[wmazz]

There have been 3 generations of Skat Trak JS650 impellers. The straight pitch
impellers were the 1st gen, and they are obsolete (a failure). The 2nd gen was
a 3 degree variable pitch, and it was not much different. The 3rd gen was the
8 degree variable pitch 8/16 and it is a very good impeller.

Your wife's ski will run fine, if you keep it stock.

But if you add a pipe, exh manifold, and larger carb, use the 8/16.


Bill M.

A 9/17 is acceptable for a pipe, exh manifold, and larger carb.

Do you want to discuss maintenance?

 

[Project101]

There have been 3 generations of Skat Trak JS650 impellers. The straight pitch
impellers were the 1st gen, and they are obsolete (a failure). The 2nd gen was
a 3 degree variable pitch, and it was not much different. The 3rd gen was the
8 degree variable pitch 8/16 and it is a very good impeller.

Your wife's ski will run fine, if you keep it stock.

But if you add a pipe, and larger carb, use the 8/16.


Bill M.

wifes ski has a few mods,
sbn 44
west coast intake
west coast exhaust manifold
west coast exhaust
west coast water box
worx top loader
ocean pro cone/nozzle.
skat 6 impller.
she's telling me she wants more bottom end, so if I end up with a different impeller would the 8/16 still be a good choice?

 

[wmazz]

The 16 is too much impeller for your set-up. It is acting like a rev-limiter and is
loading down the engine like an old car going up a steep hill. Because it is like
a hill, it is creating more heat, and possibly detonation. All it needs to push it over
the edge (maybe) is a high compression head.

During the late 80's and early 90's JS 650's used to blow up all the time. The big
differences is better impellers, and Ocean Pro heads are (thankfully) difficult to
find. Your 16' impeller loads the engine down to about ~5500rpm. So the engine
never reaches peak HP rpm, unless it is cavitating or jumping a wake.

The 8/16, or 9/17 would be a big improvement. So would rejetting the 44SBN
with reverse jetting and a high pop-off (2.0 & 115gr), it will increase power and
acceleration.


Bill M.

 

[Project101]

Thanks for the great advise i just ordered a pop gauge and was looking up a rebuild kit. (it wont idle or start easy) i assumed it needed to be rebuilt and rejetted. I'm not tracking the term reverse jetting. can you please explain?

 

[wmazz]

What have you already done to try to fix the idle and starting?

Do you know the jet specs and screw settings?


Bill M.

 

[Project101]

What have you already done to try to fix the idle and starting?

Do you know the jet specs and screw settings?


Bill M.

No I haven’t touched it yet. Just wasn’t tracking the term reverse jetting.
When and if I rebuild it I will write down what it currently has for settings.
As my base.

 

[wmazz]

There is 2 types Reverse Jetting: Low Pop-off (for racers) & High Pop-Off ( for everyone).
I prefer a high pop-off.

If you added the main jet and low jet on a hypothetical dual 40mm SBN-i carbs with
a 75 low jet and a 150 main -> 75 + 150 = 225. Any combo of low and main that add
up to 225 will possibly work.

Now lets say the hypothetical dual 40mm SBN-i carbs have 1.5mm seats and 80gr springs.
Roughly 4 low jets = 1 spring size.

Now lets increase the pop-off to ~55psi, by using a 115gr spring with the 1.5 mm needle
& seat (N&S). The 1.5 N&S is capable of flowing all the fuel the fuel pump is capable of
outputting to the carb (without causing any starvation).

Now rearrange the jetting to work with the new high pop-off, and you get: 55 psi pop-
off, 95 low jet, 130 main jet, 1.5 N&S, 115gr spring (95 + 130 = 225).

The result is more power and acceleration that is comparable to ~100cc increase in
displacement.

For a few SeaDoo models, (650, 720's with dual 38sbn-i carbs), the stock jetting used
to dribble out the main jets because they had a small venturi and an even smaller main
jet booster with an 80gr spring. These models used to load up badly in 5mph zones, and
by increasing the pop-off, and rearranging the jetting, I fixed the 5mph zone problems
and increased the power. I used the stock 1.2mm N&S, with 115gr springs, and a 76psi
pop-off.

On the race X2's I help with, we run dual 40's (stock SX800 carbs), with 1.5 N&S, 115gr
spring and 55psi pop-off. It is fast, stock 800cc bore & stroke, and has a #1 plate for the
western region.


Bill M.

 

[Project101]

Holy moly bill! , thats awsome . I will have to read that probly 10 more times to fully understand. I won’t be able to put my handS on the ski Till Labor Day.. military owns me for a bit longer. Thanks so much!

 

[kevbo]

A Single 44 on a 650 that is over loaded probably wont like 50+lbs of pop-off. That combo will have the weakest signal of anything except maybe a single carb rotax. It will end up reverse jetted with that.

 

[wmazz]

A Single 44 on a 650 that is over loaded probably wont like 50+lbs of pop-off.

You might be right, but a reverse jetted 650 sbn uses 2.0, 115gr, 32 psi. pop-off.
But if I had the time I wouldn't mind getting a 130gr spring from a ~97' 951
(white engine) and trying it. All you need is the right size low jet (~145).

All you need for reverse jetting is a proven good jet specs, and then you can
convert it. I prefer starting with a specs that use 1.5, or 2.0, with 80 gr springs.

For example: A single 46sbn for a 750 Kawi may have specs of, 120 low, 160
high, 2.0 seat & 80gr spring.

Using my guidelines for reverse jetting: 2.0 seat, 115gr spring, (+8 sizes) 140
low jet, (-8 sizes) 140 main jet.

When do you need to reduce the pop-off: When the carb doesn't transition from
the low speed circuit to the high speed circuit. How often does that happen? SO
why is the pop-off such a common topic. And why do I see people rejetting their
carbs pop-off first, instead of starting at the bottom and working up. The pilot
circuit and low speed circuit overlap with the high speed circuit.

If you use the "Idle Drop Test," you can set your seat, spring, pilot circuit, and low
speed circuit all at the same time. Then all there is to worry about is the main jet.

You can take the basic principals of what I laid out and apply them to single,
dual Mikuni sbn's. For example if you had a set dual (pos) Buckshots, and you
want more performance from them: Reverse jet them with 2.0 seats/115gr springs,
~140 low jets and (main jets - 20). It works great.

Another advantage of running a high pop-off vs a low pop-off is you don't
have problems with the engine loading up on the line, there is no reason to
lower the fuel pressure. With a high pop-off you end up with a consistent carb
that behaves as expected.


Bill M.


I used the highest pop-off example (1.2 w/115gr) because of all the bad info out
there on the dangers of a "High Pop-Off."

I used the 750 X2 example of small carbs as a successful alternative to big carbs.
People seem to gravitate to the idea that bigger is better. Bigger pipes is another
dumb idea.