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03-21-2011, 05:09 PM #1
- Join Date
- Oct 2006
- Cleveland OH
What you need to know about Polaris 650 750 780 785's
First I'd like to welcome you to Greenhulk.net
Chances are you're new to PWC or are just looking for tips or tricks to maintain/repair your Fuji powered (blue engine) 650 750 780 and 785 (black) PWC.
Please take the time to read all the great info posted on this site in the tech section before starting a new thread and asking questions that have most likely been asked before.
Fuji engines were used in Polaris PWC from 1992-1997.
You may read terminology you don't understand. This will help you out.
When referring to cylinders (cyls) you have the MAG or front of the boat cylinder. It's labeled that because the magneto is mounted in front of it, and the flywheel is attached to it.
CEN or center is obvious in the middle
PTO stands for Power take Off and is the cyl closest to the rear. (Don't ask me why it's labeled that )
FA or Flame Arrestor is what most would call the air filter. It doesn't actually filter the air, it actaully prevents fire from shooting out the carb in case of a backfire. Air filters aren't needed as you normally don't have dusty conditions over water.
PULSE FITTING or PULSE HOSE. This is a fitting on the engine case with a hose that goes to the fuel pump and operates it by using positive and negative pressures.
STATOR gets confusing. 1 stator is actually the magneto, but we call it the electrical stator. And the other stator is actaully the section of the jet pump that the impeller mounts to and has the vanes for straightening out the water after the impeller swirls it.
CDI stands for Capacitator Discharge Ignition and is the small black box inside the electrical box that controls your engine timing. The entire electrical box is not known as the CDI.
Multi Function Display or MFD. Digital dash/instrument that displays your fuel, and oil levels, trim position if you have that, overheat and low voltage warnings, clock, speed, tachometer, hours on unit, and some display the maximum speed and RPM for the most recent ride. Also know as the "Dream O Meter" because they tend to display higher top speeds than actual GPS readings.
COMPRESSION TEST is the amount of PSI a piston will create when using a compression gauge. Used to determine cylinder condition. Low compression would be considered 110 PSI or less. Good compression should be around 120-135 PSI. High compression would be around 145 PSI and up requiring premium fuel or better.
LIMP MODE is when your MFD is reading low oil, low fuel, overheat, or low power (battery not charging) and it restricts the engine from going faster than 4200 RPM. It does this in an effort to get you back to the dock by conserving fuel, keeping temperature down, and using as little oil as possible. 650 and 750's DO NOT have Limp Mode, only the 780 and 785's that use the Fuji engine have this option.
LEAK DOWN TEST is when you seal the engine air tight and place it under a vacuum using a hand held gauge. You're basically looking for air leaks inside the engine that can cause piston damage.
PISTON WASH is a means of determining how much fuel a piston is getting while the engine is running. It's an actual observation you can see with the eye and is used to help "tune" an engine for peak performance or reliability.
RICH is when you have too much fuel for the amount of air inside the combustion chamber that results in poor performance and fuel economy.
LEAN is when you have too little fuel for the amount of air inside the combustion chamber. This makes temperatures rise and pistons will actually melt or erode if ran like this continously.
CRANK INDEX or PHASE is referring to the 3 pistons in relation to position of one another. Ideally each piston should be EXACTLY 120* apart on a 3 cylinder.
HYDROLOCK is when you get enough water or fuel (any type of liquid) inside the combustion chamber. Liquids don't compress as the piston comes to the top on the cyl., so usually the piston, or connecting rod will fail, or the crankshaft will twist and come out of phase/index. Often happens when a ski is rolled over in the wrong direction, water is sucked into the carburetor, or the engine case fills up with fuel or oil.
DETONATION is a cause of piston failure. http://www.greenhulk.net/forums/show...highlight=deto
Please refer to this link when looking for a picture of the autocock that is to be removed, or the restrictor located inside the return hose. Post #2 http://www.greenhulk.net/forums/show...urndown-Basics
Please refer to this link when looking for pictures of the fuel system or carburetor manual.
Due to their age alone, the fuel system should be updated or upgraded.
1992-1995 most models had fuel hoses that were inside the fuel tank that are notorious for rotting and falling off.
Fuel hoses may look fine on the exterior, however, they tend to fail from the inside-out. Clogging and restricting the fuel passages that can lead to major engine damage.
Your fuel hoses are 1/4" I.D. and 20' usually takes care of a 2 seater ski. (about $20) They should be of good quality, not the cheap clear hose you buy off Ebay. I personally prefer the braided reinforced fuel hoses you get from an auto parts store, (DO NOT buy the $5 ft hose for fuel injection) but many others like to use a quality clear fuel line from a reputable supplier. Keep in mind that there is a hose that goes from the engine pulse fitting to the fuel pump, and that should be replaced as well. Keep that hose as short as possible (no longer than 12") and making sure there are no kinks or bends in any of the lines.
In the 1994 and 1995 650 and 750 PWC, there is a small brass restrictor found inside the return hose going from the carbs back to the fuel tank. Also in that pic above (link posted earlier) is the Autocock, and it is to be removed per a Polaris bulletin, and the hose capped air tight. They were prone to failure and causing piston damage.
The brass restrictor is located approxiamtely 1" past the last carburetor inside the fuel hose. This MUST be re-installed in order to create fuel pressure. If you do not have 1, one can easily be made from a carburetor jet and a brass hose connector. Post #4 http://www.greenhulk.net/forums/show...highlight=made
If your ski came with external fuel filters, just replace them. They are cheap enough and it's good insurance. (about $8 ea)
The petcock or fuel shut off valve should be inspected/rebuilt/or replaced all together. There are rubber parts and O rings inside that get brittle, swell, or physically move which can cause fuel starvation and lead to damage. A Sea Doo selector valve ($15) will fit fine, it's just the arrow direction will be off.
Newer models have a fuel filter built into the water seperator. They also have an orange ring that floats as an indicator if water is present inside the fuel. Older models have just the water seperator with no ring or fuel filter, so you must actually look for water in the bottom of the bowl. Inspect both of the them periodically. (water is heavier than gas, therefore it sinks to the bottom of the bowl)
Your 650 and 750's used a round (35L per hr) single outlet fuel pump. The internals get worn and cause you to lose fuel pressure leading to piston failure. I recommend you install a new triple outlet fuel pump. What that does is restores lost fuel pressure due to age, and also supplies each carburetor individually VS. the single that feeds the first carb, then the second, and finally the third. The new round triple outlet (35L per hr) can be bought for around $35. See above link for new hose routing.
The 780 engines came standard with a pentagon shaped High Output (65L per hr) triple outlet fuel pump. Anyone with a 780 should just rebuild VS. replace their fuel pump. A rebuild kit costs around $20 while a new pump runs around $65. Please note that you should only use GENUINE MINKUI parts when rebuilding. It's quality stuff that's lasted for many years. Now is not the time to try and save a few dollars on cheaper aftermarket parts.
Pro 785's use 44mm carbs that have the fuel pumps integrated in the end carburetors. The surplus fuel from both carbs then feed the CEN and the excess returns back to the fuel tank. The Super BN 38/44mm rebuild kits (same as the 650/750/780 use) will have the parts for the fuel pumps included with them.
Carburetors at this age should be rebuilt. Them looking clean inside, or pouring carb cleaner in the fuel tank isn't going to do squat. You need to open up the carbs, replace the old parts, clean the fuel passages, and replace the internal filters on the back side. Yes, there are filters INSIDE the carbs as well. You will need 3 genuine Mikuni carb rebuild kits for a Super BN 38/44mm carburetor, (around $45 ea) which is what you have. 1 kit handles 1 carb, and you have 3 carbs. Not included in the kit is the needle and seat, of which you will again need to buy 3 of. They are a size 2.0 "push in" type for a Mikuni Super BN. (around $15 ea)
Finally there are 2 fuel tank vents that located just below the steering console or hood. 1 allows air INTO the fuel tank and is "T" into the vent hose. Almost looks as if there should be a hose attached to it, but there isn't. And the other is mounted directly into the rubber grommet inside the console that vents out to the atmosphere. It should release any excess pressure built up inside the fuel tank. (opens at 1.5 PSI) If this valve fails to open, you can have excess pressure inside the fuel tank that will force fuel into the engine if you fail to turn the petcock (fuel selector valve) to the off position.
You should only use a good quality TCW III 2 stroke oil or a fully synthetic oil specific for your application in your PWC. Not all oils can be used in oil injection units, so pay attention to what you buy.
If you use the stock oil injection system, make sure to replace the 1/8" I.D. oil hose and clamps. Many costly engine failures occur because of a $.06 hose clamp broke or the hose cracked/kinked/fell off.
You should replace the oil filter just because of age as well. (about $8 ea)
If you choose to remove the oil pump and go with premix, you should remove the oil pump and the internal gears. You can buy a block off plate, or make one just as easy from a piece of aluminum laying around the house. Just be sure it's sealed air tight after you install it.
You will want to run the premix at a ratio of 40:1 under normal conditions and 32:1 using regular (non synthetic) oil when breaking in new piston rings. Synthetic is too slick to properly seat the rings.
Then you have 3 choices of what to do to prevent the MFD from warning of low oil.
1. Leave the oil tank full and clamp off the oil hose.
2. Tie the oil sender float in the "up" position and store it out of the way.
3. Install a 40 ohm resistor between the oil sender wires. This works great if you do it inside the elec. box.
Last edited by xlint89; 03-22-2011 at 09:35 PM.
03-21-2011, 05:40 PM #2
Stick it. Thanks for taking the time to help.
03-21-2011, 06:33 PM #3
Telling him to stick it????? thats not very nice........
03-21-2011, 08:41 PM #4
- Join Date
- Jul 2007
- Toronto, Canada
In addition to the excellent information posted here, click on the signature links below for even more useful info.
Last edited by K447; 05-17-2011 at 10:29 AM.
03-22-2011, 09:29 PM #5
- Join Date
- Oct 2006
- Cleveland OH
Please refer to this link for burnt, cracked, melted, or a hole in piston.
Most of the causes listed in that link could be solved by performing the fuel system upgrades. Things like the obstruction in fuel lines, restrictor missing, and dirty carbs or filters can be easily resolved.
Incorrect Carb Adjustments can lead to a poor performing engine or possible piston damge. Please refer to the settings for your year and model ski.
Post #12 is not complete, but covers alot of the models. http://www.greenhulk.net/forums/show...es-Carbs/page2
Wrong spark plug heat range. NGK runs backwards from most other manufacturers. The lower number is actually hotter. Some of the older models recommend using the NGK BPR7ES spark plug. We have found the BPR8ES works just as well, and gives a little more room for error as far as heat related piston damage.
Engine Timing can cause engine damage from excessive heat due to too far advanced ignition timing. An incorrectly installed magneto/electrical stator or a different CDI from another model may advance the timing. Refer to a repair manual for proper testing procedure.
Out of Phase Crankshaft. Your crank is press fit together, not a single piece and bolted together like a car. What that means is a hydrolocked engine or an obstruction (stick or rock) that gets lodged in the jet pump can twist the crank. If that happens, the piston that came out of phase can get damaged for no apparent reason. There are easy tests that can be done with the engine inside the hull. Post #4 http://www.greenhulk.net/forums/show...redneck+method
Air Leaks inside the engine lean the air/fuel mixture out to the point it runs hotter and damges pistons or may even lead to detonation. A leak down test will tell if your engine is sealed air tight. http://www.greenhulk.net/forums/show...ight=leak+test
Piston Wash is a great indicator of a potential problem. It can show you if you're running lean on fuel and heading towards piston damage, or if you're running rich and not getting peak performance. It's as easy as removing the spark plug and placing a very small (usually flexible) flashlight or borescope into the cylinder. Remove the spark plugs and plastic engine coupler cover. Turn the engine over by hand until the desired piston is at it's lowest point. Insert the light/scope into the hole and take a look at your piston dome. http://www.greenhulk.net/forums/show...ht=piston+wash
Another common problem seems to be the ground wire inside the wiring harnes melts down. First make sure your battery cables are tight and have clean connections on both the battery and the engine plate where the ground wire connects. Most models should have a plastic cover between the battery and the aluminum elec box. If you do not, get one or place something nonconductive between them. It appears the aluminum box may short out between the battery terminals and cause the ground wire to melt.
Multi Function Display doesn't turn on. Inside the elec box is a 1/4 amp fuse, check that with a multi tester. Sometimes it's hard to see the break in the fuse. Replace it with another 1/4 amp fuse ONLY. (can be found at radio Shack) Anything higher will damage the expensive MFD unit.
MFD always reads low fuel even with a full tank. The float inside the pick up tube gets saturated over time and doesn't float. You can buy a replacement float for around $25.
Limp Mode is when the red light blinks on the MFD and the engine won't rev over 4200 RPM. It's activated by low oil, low fuel, overheat, or low power. Correcting the problem will get you back up and running, but there is a way to bypass the limp mode. If you go inside the elec box and remove the gray wire from the elec. board it will bypass the rev limiter. THIS HOWEVER IS NOT A FIX!!!!!! Bypassing the limiter leaves you open for catastrophic engine failure, or running out of fuel. Both of which can leave you stranded out on the water. Once again, FIX THE PROBLEM and re-install the gray wire inside the box.
Weak Spark can often be cured by removing the spark plug boots and trimming the plug wires back about 1/4" or so to expose clean wire. Then rescrew (the boot terminal is threaded) the boot back on and zip tie it in place.
Stalling, hesitation, surging, or making the engine run better by pulling the choke can normally be fixed by rebuilding the carburetors. Fuel sytem issues are the #1 problem with these skis.
Ski revs up but doesn't go anywhere. First check your intake area by the jet pump for debris. Next if you have a rubber dampned engine coupler (black) under the plastic cover, look for signs of rubber shavings. Due to age, the driveshaft will slip inside the rubber, and won't transfer power to the impeller. Finally inspect the drive shaft splines on both ends for signs of wear (pointed or damaged), and check the engine coupler and impeller splines too. DO NOT put your finger inside them. You may get a nasty metal splinter if they are bad.
05-17-2011, 07:26 AM #6
- Join Date
- May 2011
THANK YOU SO VERY MUCH APPRECIATED!!!! Doesn't look promising before Memorial Day weekend !
I'm on the East of End of Long Island.
05-28-2011, 10:52 PM #7
- Join Date
- May 2011
i am having some trouble with my 1994 polaris sl 750 ski, i bought it yesterday from a guy that said it ran fine i took it out today and got on the water it did run but you it was just putting along when id try to get on it it would shut off or slow down it would go about 15MPH tops any body know what it could be? it also will not just idle without giving it gas or it will shut off? this is my first ski ive always messed with fourwheelers and dirtbikes so im kinda of new to the whole seadoo thing would like to know if you had some tips or some direction i could go! thanks!
05-28-2011, 11:19 PM #8
- Join Date
- Jul 2007
- Toronto, Canada
06-21-2011, 12:39 PM #9
- Join Date
- Mar 2009
Same old wiring problem..
I has burned some wires from the electricalbox to the stator/starter on my SL750 from 95..
I was just wondering if you guys know wheater a box+wiring from a 93 will fit on a 95..??
thanks in advance..
JP :: Denmark
06-21-2011, 05:16 PM #10
- Join Date
- Oct 2006
- Cleveland OH
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