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  1. #1

    polaris 750 new pistons

    the middle piston has burn a hole. now i have read enough to know that this is a problem due to the fuel pump. but before i go and get all started with questions, and belive me i have many.

    the jet ski was gave to me for free, guy simply did'nt want it sitting around. He has had all 3 pistons replaced at one time or another, #1 looks new, the #2 is burned and #3 looks like #2 but in really good shape.

    I dont know the year or any info on it other then it's a polaris 750. I'll round up some more info and see if i can get a manual and where do i get parts for this? it's an older ski.. i looked threw the net and could'nt find the triple pump, and i'm really good with google.

    i think since i have no money in it i'll just start fresh, all new gaskets and parts, and delete the things that need to come out, looking like a project to me.. what do you think?

    thanks much
    jon


  2. #2
    i wanted to throw it out here that i'm really good a wrenching, but i'm lost on all the watercraft lingo, and the lack of 2 stroke knowage does'nt help. reeds? umm right..

    not to worry, i'm never skeerd and aways willing to learn. i need some manuals of this ski.

  3. #3
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Welcome to the Hulk Jon! You can find the manual and more here.

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome to the Hulk

    Definitely start by downloading the service manual

    Model year is the last two digits of the HIN number plate on the rear deck.

    For your Fuji engine, a good place to start would be this Fuji Engine web page.

  5. #5
    bnasty's Avatar
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    Can you post up some pictures of the pistons and cylinder heads pls?

  6. #6

    i think it's a 94 slt 750

    i'm going to guess that this is a 1994 polaris 750 slt. as you can see from the pictures it's in need of some tlc. free none the less and ran great untill the hole there in the middle piston.

    forgive me i dont know all the pwc lingo..
    i should have added a picture with all the pistons showing, #1 is new and is over sized, but does not have a number saying what size it is. the middle and last piston are marked with 0.75, guess these have also been bored. also looks like someone took a shot at t-ing into the fuel lines. it has the stock fuel pump.

    i got this ski just as it sits, no trailer and alread torn into.

    so basically everyone here knows 10x's more about this ski then i do at this point, and please be lingo friendly. i have no clue what mag, reeds, pto and so on are.

    i'm new to 2 stroke and marine engines all together.

    altho is needs some work, i think it's well worth fixing.

    again thanx a million,
    jon
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  7. #7
    Quote Originally Posted by bnasty View Post
    Can you post up some pictures of the pistons and cylinder heads pls?
    i'll get you some more pictures of the other cyl's and the heads too. they look alright, just that hole in the piston. then again.. i'm new to 2 stroke

  8. #8
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Lingo? No problem. We will be kind.
    Post up some more pics with the other domes off, fuel lines, and pump.
    The head gasket on the center is a little mis-positioned. The little shark fin tab on the gasket should be positioned under the water outlet port on the head. Turned ccw one bolt. The front cyl, is called the mag, for magneto, and the rear cyl is the pto for power take off.
    Typically if the are no size markings of the piston, it's standard size.

  9. #9
    Click avatar for tech links/info, donation request K447's Avatar
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    Arrow Cylinder naming, 2-stroke engine basics

    Quote Originally Posted by jsmith564 View Post
    i'm going to guess that this is a 1994 polaris 750 slt.

    ...looks like someone took a shot at t-ing into the fuel lines. it has the stock fuel pump.

    ...please be lingo friendly. i have no clue what mag, reeds, pto and so on are...
    We have all been where you are - unfamiliar lingo, unfamiliar mechanical things. Sometimes we forget, and over run new arrivals with too much technical stuff, too fast.

    I think there are some older threads around her that cover the basics. Perhaps someone else can post a few links

    The cylinders are always numbered and named starting at the front of the engine.

    Number 1 cylinder is at the front.

    Mounted down on the front end of the crankshaft is the flywheel housing, with the flywheel inside. Inside the flywheel is the Magneto, which generates the electrical power to run the electrical system, and signals the ignition to fire the spark plugs at the appropriate times. The front cylinder is often called the MAG cylinder, short for Magneto.

    The rear of the engine is the where the drive shaft connects. This is called the Power Take-Off end of the engine, or PTO. So PTO is the number 3 cylinder (on a three cylinder engine).

    The middle cylinder is the Center cylinder, or CEN.

    The tee connections in the fuel lines was a common attempt to 'fix' the weak fuel delivery problem, without replacing the single outlet style fuel pump. We now know that the tee fix wasn't enough, and the triple outlet fuel pump upgrade is the proper fix.

    There is some good info available describing how these 2-stroke engines work.

    Your Polaris engine is actually three single cylinder engines, working side by side, all driving a shared crank shaft. For many things on the engine, you will have three of them. In general, all three cylinders must be working the same, in unison.

    Below each carburetor is a curved intake manifold, that directs the air flow into the base of the engine. Mounted right where the air enters the engine are reed valves, which use thin flat strips of semi-flexible material. They look something like the flat reeds in a musical wind instrument.

    The air flow from the carb flexes the reeds open, and the air+fuel mixture enters the crankcase below the cylinder. The reeds then snap closed, and the air+fuel mixture is trapped, and then forced upwards into the upper part of the cylinder. Up there, it is compressed, spark ignited, and combusted to power the engine.

  10. #10
    thank you for being kind to me. i've been looking over the manual... alot of info in that thing.

    i was trying my best as guessing what the lingo refers to. thank you for clearing it up. I think i should be able to pick up quickly.

    i'll round up some pictures of all the mess. lol

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