09-12-2011, 09:26 AM #1
1994 Polars 750 SLT Rebuild Project - Piston Wash
Top left is MAG, top right is CEN, bottom left is PTO. Running 32:1. Plugs were wet, but idled back to dock, did not do WOT plug chop. Top numbers were 46.8 MPH @ 6180 RPM. Having hesitation issues out of the hole, but plan on doing a carb rebuild over the winter. Fuel system fully updated. MAG and PTO Pistons were new. CEN was in the machine when I got it, and was already dark from previous owner with no signs of wash.......
09-12-2011, 09:43 AM #2
Im not a pro, but all are lean. Mag has some wash starting, maybe turn it up an 1/8, other two need at least an 1/8 turn, maybe closer to 1/4.
09-12-2011, 10:38 AM #3
Mag = a little lean. Give it an extra 1/8
Cen = Extremely lean. Give it an extra 3/8
PTO = Very Lean. Give it an extra 1/4
09-12-2011, 11:29 AM #4
Also applies to the other two with the new settings - will a new wash appear? Do i need to somehow "clean" the piston domes?
Thanks for all the input!
09-12-2011, 01:58 PM #5
Yes, over time a wash patter will develop. There is no need to chemically or mechanically clean the tops of the pistons.
If you're too rich it's no big deal.....you'll just be down on RPM. If you're too lean, watch out because you just might burn up a piston.
09-12-2011, 02:01 PM #6
If I was running at 6180 rpm, and make the changes suggested, what should the anticipated change in RPM be? Substantial or minor?
Can you give me a guess on what "over time" equates to in machine hours...... I want to check again, but don't want to pull the heads again until it has had enough time to generate a new wash pattern.....
Definately don't want to rebuild again, that's why I am trying to be careful.......
09-12-2011, 02:50 PM #7
Was this speed with a GPS, if so your speed is very good for that rpm, does machine have stock impeller in it? I wouldn't run anything richer than 40:1 ratio if premixing, remember on this ski the oil before did not run through the carbs as the later models, you are now running the oil & gas through jets meant for just gas, it isn't a big difference, but can be enough to lean out the fuel a little & todays fuel quality doesn't help. Also does the ski have to stock flame arrestor the one with the big opening to the back, if not then more fuel is needed. Fuel & fouled plugs still cheaper than pistons!
09-12-2011, 03:06 PM #8
Dream-O-meter. The pump is from a 95 SL and has a 4 blade impeller. It was dinged up and needed some filing so I was impressed with the readings, even if it was on the Dream-O-meter.
I am just now figuring out that the machine has an aftermarket FA kit on it. Has spacers with oil injectors and a one piece open sided element with blue cap. I have read that this may be an O/P FA kit and came with larger jets. However, I had to replace the carbs due to rusting, used one of the jets out of it to build a new restrictor for the fuel return, still have a spare, and simply couldn't get to the other one because of rust. I need to pull them apart now and find out what size jets the new carbs have in them. May need to up the jets to 102.5?? to go with the aftermarket FA.
09-12-2011, 07:00 PM #9
- Join Date
- Oct 2006
- Cleveland OH
KJ has really answered most of your Q's, and I agree 100%. Only thing I'd change is adding an additional 1/8 turn to his recommendations. You are WAY lean....
Lose the 32:1 premix and run 40:1. That'll fatten up your fuel as noted by Rlaceman
You're not going to see a huge gain in RPM when adjusted properly. That ski should run around 6300 RPM if the stock impeller for that ski is used.
No need to pop the heads if you wwant to take a quick peak at your wash, you can get a small flexible flash light through the plug hole to get a view of the piston tops at BDC.
You may not need to rejet if you make the adjustments and watch the wash.
It will clean the carbon off the old pistons, and it won't take too long to change either. Maybe an hr. or less of running should start to change the color.
09-12-2011, 11:00 PM #10
- Join Date
- Jul 2007
- Cedar Rapids,Iowa
Yep,yep and yep. The wash will start cleaning real fast, It's not just fuel, it's fuel on a hot surface. Think steam cleaning with hot acid.
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