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  1. #1
    97 Kawasaki STX 1100
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    A little help please! Polaris SL750

    Hey guys, just a little history first.... For those of you that don't know or remember me...PTO cylinder melted 3 pistons before I finally figured I had a bad index....

    After spending $ after $ on pistons I fixed the crank and put it back together with a used piston I picked up on eBay... Unfortunately I didn't buy new rings. The cylinder and piston are not a matched set.

    The mag and center have good compression 120 psi I never split them up or touched those cylinders. They both still look great, but the rear has 100 psi...

    Ski has been running now 3 day trips as is. Just added ocean pro filters FA and jetted carbs 102.5 as indicated in the instructions....

    I pulled the plugs I'm attaching pic looks like the PTO is running rich probably not getting good burn do to low compression... Just wanted someone to look at my pics and give me there 2 since to see if you agree or disagree with me...

    My plan is to pull the PTO cylinder back off now that I know the ski is running and hasn't melted anything and replace the rings on that rear cylinder. I'll put a light hone thru the cylinder, through the new rings on. My time and a few gaskets no biggie....

    Please see pics. I placed a small hand held flashlight in each cylinder. Looks like I have a couple small circular areas clean on the edges of the pistons as I should... I'll know more when I pull that head....

    Just give me your 2 cents please let me know if you agree or disagree and or if you have any other ideas. I did want to mention after adding the ocean pro and rejetting I noticed after running full throttle the engine would bog and hesitate when I'd try to re-accelerate. I'd stop to a idle and give it gas and the engine would continue to bog. I let it sit idle a little longer then it would take off.

    I'm assuming the engine is running a little rich at cruise and at idle a little lean so the plugs clean them selves at idle allowing me to take off again... Did not do this until after I rejetted and added ocean pro filters.... Let me add the the bog and hesitation was only after I slowed done. Full throttle ran great and even cruise. But after staying on full throttle for long periods of time once I would slow down and then re-accelerate is when it bogged and acted up... Pretty sure that fouled plug was the cause or just too rich period...

    Thanks in advance...
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  2. #2
    casey67's Avatar
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    My initial impression says the 2 plugs on the right are too cool,and probably lean.That other cylinder burn't up.
    What compression do you have ?

  3. #3
    97 Kawasaki STX 1100
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    Quote Originally Posted by casey67 View Post
    My initial impression says the 2 plugs on the right are too cool,and probably lean.That other cylinder burn't up.
    What compression do you have ?
    Starting from left to right. 100psi pto, 120 psi center, 120 psi mag. The one on the left has the low compression...

  4. #4
    WFO 4 LIFE nitrosportman's Avatar
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    man this sounds exactly like what im dealing with

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    I don't like "plug reading".

    How about a pic of the piston when you remove the head instead.....?

  6. #6
    97 Kawasaki STX 1100
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    Quote Originally Posted by xlint89 View Post
    I don't like "plug reading".

    How about a pic of the piston when you remove the head instead.....?
    Here you go. I just pulled the head and I went ahead and pulled the center head since Im here anyway.... This should clear up any question about how those 2 other plugs are running... Not sure what to think. Based on what Ive learned here Id say the center cylinder is perfect and the rear PTO is lean. Is this correct? Just doesnt make any sence to me. I was thinking my plug reading is rich but then again whats your piston wash gonna look like with low compression. Just to let you know also the pistom seams alittle loose in the cylinder compared to that center cylinder. I went ahead and mic.ed the cylinder. 69.75 It seams good so I went ahead and ordered a brand new piston (WSM)010-830K Usally that helps tighten those clearances... Heres some pics! The first one is my center cylinder the other 2 are my rear PTO.
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  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Cen is good, actually a tad rich. But I would leave it as is. (little room for error or poor fuel)

    PTO is LEAN!!!! You need about 1/2 turn OUT on your hi speed screws.

    Low compression on your PTO is not good. That's the signal that drives the fuel pump.

    Low compression = low signal

    Low signal = lower fuel pressure

    Low fuel pressure = piston failure


    Have you done a leak down test?

    Did you do the fuel system upgrades? Did you rebuild the carbs?

  8. #8
    97 Kawasaki STX 1100
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    Quote Originally Posted by xlint89 View Post
    Cen is good, actually a tad rich. But I would leave it as is. (little room for error or poor fuel)

    PTO is LEAN!!!! You need about 1/2 turn OUT on your hi speed screws.

    Low compression on your PTO is not good. That's the signal that drives the fuel pump.

    Low compression = low signal

    Low signal = lower fuel pressure

    Low fuel pressure = piston failure


    Have you done a leak down test?

    Did you do the fuel system upgrades? Did you rebuild the carbs?
    Yes to all your questions except the leak down which I really had no reason to suspect since the whole engine has been apart and resealed with all new seals front and rear etc.. Carbs rebuilt last yr and just had them apart again for a rejet 3 days ago. Index was checked during reassemble last yr. Ski has no hrs on it..

    You helped me with this ski last yr when I went thru several PTO pistons due to a PTO Index that was off. The whole ski has been disassembled, all new seals etc and a used Crank from a SL650 in great condition....

    I had reassembled the ski with a used piston for the PTO, purchased thru eBay and a set of used rings I had laying around. I was so aggravated with the amount of money I had already spent on pistons I didn't want to poor anymore money into it until I was sure.

    I haven't burnt any pistons so I'm ok spending a little now to get it to 100% now. The cylinder was one I had from melt down the last time I melted a hole in the piston but looked ok..

    That Rear PTO carb adjustment is set to factory 3/4 turn and has 102.5 main jets in it for the ocean pro Vortex FA . The ski was ran for about 1 1/2 hrs with the new jets installed.

    I'm guessing as I said earlier the problem is that used piston and rings.... I just purchased a new piston and ring set . What do you think? Is that gonna fix my problem or am I gonna still have a lean issue if I don't richen that PTO Carb?

    I may need to recheck my carb gaskets too since Ive had them off 2xs and reused the gaskets each time....

    Tell me whats the easiest way to do a leak down check and what areas will it check? If I had a vacuum leak on that rear cylinder could cause a lean issue.

    I do have all brand new rear engine seals and I'm very confident that wont be a issue. I did the work and I'm very meticulous. Ive been a automotive technician for over 20 yrs.

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    In all honesty, anytime you do any engine rebuild, you should do a leak down test. It costs you nothing and can prevent a major problem later.

    I'm not knocking your skills, but even the best have had an issue before. Sometimes they miss something and sometimes it's a faulty part. Being an auto tech, I'm SURE you've had bad parts come right out of the box before....

    Reason I ask about a leak down test is because the PTO crank seal is a "known" part to fail and cause major issues with running lean on that cyl.

    FYI: and that PTO is usually the most common to be out of index/phase because it's most common to have water ingested into that carb and causing hydrolock.

    Anyways.... What crank seals did you install? Most feel the OEM are the best available. One of those you get what you pay for type things with cheaper aftermarkets. Just like Mikuni carb rebuild kits, OEM crank seals are the only parts to use IMO.

    Leak Down test.

    http://www.greenhulk.net/forums/show...leak-down-test

    You can substitute the racquette balls for any type of block off plate.


    A piston or rings isn't really going to affect the amount of air fuel that enters the chamber, so I can't see that causing a lean situation.

    You're still going to have an issue unless you richen the carb settings. Fatten that boy up until we get this figured out. Safer to be rich and not damage a piston VS running it as is and holing another one.

    Do you have the restrictor installed into the return hose? (just thinking out loud)

  10. #10
    97 Kawasaki STX 1100
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    Quote Originally Posted by xlint89 View Post
    In all honesty, anytime you do any engine rebuild, you should do a leak down test. It costs you nothing and can prevent a major problem later.

    I'm not knocking your skills, but even the best have had an issue before. Sometimes they miss something and sometimes it's a faulty part. Being an auto tech, I'm SURE you've had bad parts come right out of the box before....

    Reason I ask about a leak down test is because the PTO crank seal is a "known" part to fail and cause major issues with running lean on that cyl.

    FYI: and that PTO is usually the most common to be out of index/phase because it's most common to have water ingested into that carb and causing hydrolock.

    Anyways.... What crank seals did you install? Most feel the OEM are the best available. One of those you get what you pay for type things with cheaper aftermarkets. Just like Mikuni carb rebuild kits, OEM crank seals are the only parts to use IMO.

    Leak Down test.

    http://www.greenhulk.net/forums/show...leak-down-test

    You can substitute the racquette balls for any type of block off plate.


    A piston or rings isn't really going to affect the amount of air fuel that enters the chamber, so I can't see that causing a lean situation.

    You're still going to have an issue unless you richen the carb settings. Fatten that boy up until we get this figured out. Safer to be rich and not damage a piston VS running it as is and holing another one.

    Do you have the restrictor installed into the return hose? (just thinking out loud)
    Hey I really appreciate your experience and willing ness to help.... I do have the restrictor in the return line.... Your right though If Im running lean in that cylinder I eather have a leak or carb issue.... Gonna have to figure it out..... Let me ask. So Im suppose to remove the carbs to do a leak test? and plug the intake with tennis balls? Where do I insert the air? Should I do a regular automotive leak down thru the spark plug hole? If so What do you want me to plug? Exhaust? carbs-intake? Is there a thread here telling me what exactly I need to do.... Im familiar with a leak down on a vehicle checking for intake valves, exhaust, head gaskets etc and I even have the tool........ WHat pressure should I imput in the engine. Where should it leak? Hope Im not asking dumb questions its just honestly Im a 4 stroke guy not a 2 stroke guy. Although I will be before long... LOL

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