94 SL 750 is winning the battle...

[Tazass]

94 SL 750, new SBT engine, carbon tech reeds, removed choke plates, 35 lph 3 outlet pump, rebuilt carbs, POP was 16, now 12psi, lowspeed jet was 75, now 80. New flame arrest, Solars Xprop PA-SC-X (14-21).

Trying to get this darn thing running correctly since all the work ive done above. It runs great up to 4800rpm, but I can’t get it to reach max rpm, which I believe is around 6300rpm. The best I can do is 4800rpm, unless it hops out of the water, gives it a chance to reach about 5800rpm, and holds it. I have done everything there is to do with the high-speed screws, didn’t help at all.

I think its either the new SBT engine, witch the Polaris mechanic think has a twisted shaft. He wants me to pull it and bring it in so he can throw a degree wheel on it to tell for sure (free of charge). Since its a new engine and I really don’t want to pull it out, I did the test Bryan told me to do which is line the #1 @ TDC and checking to see if #2 and #3 are even. Did test many times, they looked dead even too me.

Or its the new Solars Xprop PA-SC-X (14-21), over propped or something. Should be a good impeller for that ski. Checks out on the site.

I am running out of ideas, patients and money!! HELP!! [img]graemlins/crying.gif[/img]

Thanks
Tim

[Wet Wolf]

Way overpropped, that application is for the 780 and 785 motors, I would go with a skat 12/17, or 13/18 swirl, or possibly a PA-CD (12/18).

[mikeSL650]

hi ,
what is the web site for solars prop, please?
Mike

[Wet Wolf]

heres the main page
http://www.solas.com
then go to pwc parts

[ July 04, 2002, 01:06 PM: Message edited by: Wet Wolf ]

[Skexies]

It wasn't until I raised compression and ported my SBT 750 that I started pushing the top end of my ST 13/18 swirl.

Now I'm just hitting the rev-limit, so either more prop or higher rev limit.... sigh... always something...

[SeaLion]

Did you ever put a 92 pipe on it? A Pro785 cdi will work. Get ready for a big bottom end boost from the timing advance down low.

[Skexies]

Nope, I never spent tons of time to track down the dry pipe. It seems to be doing very well with the factory pipe.

More bottom end? ack... I have to hang over the front while trimmed down and modulating the throtle when launching in order to try and keep it from flying out of the water.

I heard that the SL750 ignition curve is more advanced than the SL780, but I don't know in comparison to the pro785. I do have the pro785 cdi, but I have not installed it yet... I'm not in the mood for re-timing the mag so I can install it, and I also am lacking that dry pipe that needed the higher rev room.

Actually, I'm considering trying to run a steeper prop pitch [assuming the sl750 pipe's lower power band couples with the new prop well] to get the acceleration calmed down into "usable" a bit more and perhaps gain some top end without peaking the revs like I am now.

Of course, I don't want to make a mi$$$take with parts selection.

Hey, btw... NICE paint job. Love it!

[ July 23, 2002, 08:22 PM: Message edited by: Skexies ]

[jetranger]

Once again I'll quote the Factory service Manual.
Pitch on the stock sl750 (1993) is 17/20. Imho
there is no way you're over propped and
explains why you have so much bottom end.
Even the 1993 sl650 has a 15/18 pitch.
I doubt there is a big difference in power
between these years. If you really wan't to
max out this thing, it's time to look into
some EGT's, without them you may never get
your ski tuned right.

[SeaLion]

jetranger, Skexies has a 94 or 95 SL750. It is different than the 93 SL750 in that the pump, pipe and powerband are totally different. A 13/18 swirl is a great impeller for a 94-95 SL750. I guess with the porting, the rpm went up and he needs to prop up or get that pro785 cdi on there.
Skexies, the SL750 cdi is not advanced more than the Pro785 cdi down low. The Pro is at 32* at 3000rpm while the SL750 is 24*-25* at 3000rpm. The SLX780 cdi is at 28* at 3000rpm. The 94-95 SL750 however is ported stock to give good bottom end and mid range.

[Wet Wolf]

factory part # 5131371 pitch is 15/20. one of the few "progressive pitch" wierd looking wavy thing impellers that polaris actually listed the pitch of. the thing you have to remember is that its not just the final pitch of the prop that makes the difference. the spread between pitches also means a lot. the wider the spread, the more ponies you need to pull that big wheel through the midrange --TORQUE--
93 750 used a 17/20, 3 deg spread, easy to pull, made up for the inefficient pump. which had no midrange or low end, but at least the top speed was OK.
95 sl 750 used a 15/20, 5 deg spread which helped the low end performance (15 deg), the midrange performance (5 deg spread), top end was about the same (20deg)
polaris also made pn#5131092, and 8/20 (12 deg spread!!!!!)wild *** 4 blade that took a ton o tork to make work. if you didnt have enough, then it was like your rpm hit a brick wall.
i would think that a 14/21 might be a little much for the mods performed on Tazz' boat.

course that just my 2 cents worth, dont get me started on pumps

:D

[ August 10, 2002, 03:35 PM: Message edited by: Wet Wolf ]

[Skexies]

Sealion, wow, cool information on the CDIs.

Also, cool info props.

Yes, it was a 95 sl750, but I now have the extended pump setup on it along with the 6 vane stainless stator and the R&D intake grate. The compression was raised for 92+ octane, engine & cyls ported, [still staying with the SBT +1mm pistons], R&D intake, pro 785 carbs / manifold, 3/8" spacers, carbon tech reeds, TDR waterbox, and a triple probe egt.

Now that timing information makes me want to swap cdis if pushing a slightly larger prop works out... like a 14/19 or a 15/20 swirl... ahhh decisions decisions decisions...

[Skexies]

About tazass's deal.... sounds like if you hold the speed after out of the water, your engine setup doesn't have the torque needed to get up in the higher power range of the motor. Once you jump up out of the water.. you spin up into the power range and your motor can hold it.

I guess that would say, increase the torque of the motor or decrease the prop. ;)

[Wet Wolf]

Skexies, if your bangin the rev limiter, the AAT can pull your top rpm down far enough to make that stop. It will turn your over rev into speed without losing any of your low end and midrange. [img]smile.gif[/img]

[Skexies]

Hmmmmmm... AAT or 14/19? As it is, I have to modulate the throtle fairly heavily out of the hole so I don't pop out of the water and suck up air...

I thought maybe the 14/19 would bog me a bit more on the low side and give me more speed on the high side so I can be a bit more brainless on the gas. [img]graemlins/buck.gif[/img]

How much is the AAT?

[Wet Wolf]

an AAT for your boat is $190..... cheaper than a prop.