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  1. #1

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    Intake gasket needed on SLT 750?

    I just bought two hulls and 4 boxes of parts that were supposed to be a pair of '94 SLT 750's. I got them together and actually got them running. However, I ran into 2 issues that I need help with. It seems that someone before me changed the stock airbox out to a 780 style open box. In doing so, they disconnected and plugged the oil lines going to the base of the carbs, and attached the oil lines to the ports on the air box. However, everything I see says the oil injectors are built into the air box. These are not. They are a separate piece, like a spacer under the airbox. I can not find a reference to them anywhere. My first question is, are they supposed to have gaskets under and/or over them? They have none. If they need gaskets, what model of ski do I order them for?

    My second issue is that I went to the lake this weekend. I got this ski started, but it just wouldn't go. After tinkering with the carbs for about 3 hours, I got it screaming. It ran great all afternoon. We put it up on the trailer that night and went to camp. When we woke up in the morning, it would not even turn over. It turned out to be that two of the cylinders and apparently the entire crankcase was filled with gas. We dumped about 2 quarts out. What could possibly cause this? When I built the ski, I replaced all gas lines and installed a new triple outlet pump.


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk.

    Anything below the carb should have a gasket. Try making your own from gasket material from an auto parts store for $5.

    Pics would also help.

    Fuel tank vent not installed, or clogged would pressurize the fuel and push it into the carbs, if the petcock was left open.

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome to the hulk

    Sounds like you had something of a puzzle to put together. Do you have the Polaris Service Manual?

    Does the flooded machine have a fuel selector valve (fuel shut off valve)? If it is left on, and pressure builds in the tank, it can force fuel into the engine through the carbs.

    The fuel tank has two one-way venting check valves. One allows air into the fuel tank, and just hangs off a tee inside the hull.

    The other vent valve allows excess air pressure out of the tank, and is connected through a hose to a fitting that vents outside the hull.

    Make sure you have these two valves installed, and that they are oriented in the correct direction. There is a little arrow head, that indicates flow direction. Vent in from inside the hull, and vent out to the outside.

    There is one more of these, that allows air into the oil tank.

    If you have these valves in backwards, or they are missing, or incorrectly hooked up to the fuel tank, then the fuel tank can over pressurize.

  4. #4

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    Exclamation Follow up with pics

    Here are the pics of the oil injectors. The first one was cover removed but spark arrester in place. The second one is air box off, but injectors in place. The third one I am holding one of the injectors in my hand. This ski had the gaskets on both sides of the injectors, so I guess I have to try and figure out what ski they came off so I can get the right ones.

    I am a firm believer in manuals, and that was one of the first things I did. I am still looking for an operators manual. Both skis have the vent in the tank on the vent line, but no other vent. The four lines coming out of the tank are: 1. Main line going to selector valve. 2. Reserve line going to selector valve. 3. Return line going to return (upper) rail of carb rack. 4. Vent line going to a small vent below steering, under hood. This one has the valve installed inside the tank. There is a small vent on the oil tank, bout nothing else on the fuel tanks. If I need to put one in, where would I tee it to? The return line? Can't go on main or reserve, as vacuum would be pulled away from the tank, can't go on vent line, as one-way valve (out only) would negate the effect of letting air in.

    Putting them together wasn't bad at all, as I'm a fair-to-middlin' mechanic. The toughest part was that even though I had four boxes of parts, I came to find out that there were still several parts missing. Had to figure out what WASN'T there and track it down. Tough job for a big ol' ugly Polock.

    You guys rock. Thanks for the help and all the great thousands of posts I've been trying to sift through.
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  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Looking at the 1994 fuel system diagram (below), I see it predates the deletion of the auto-fuel-cock, and doesn't have the two vent valves that the 1995 model has (second diagram).

    I would suggest you use the 1995 layout, as it reflects an improved design.


    As you can see in the 1995 diagram below, both fuel tank vents are tee'd into the same vent connection on the fuel tank.


    At the very least, delete the auto-cock, as it was identified by Polaris as causing problems.

    You might also want to peruse the Service Bulletins for the 1994 (and 1995) SLT 750. You may find other issues that need to be updated or changed.

    1994 Polaris Service Bulletins
    PWC-94-01 1. Spark Plug Caps Improperly Installed on the Coil High Tension Leads
    2. Insufficient Torque on Cylinder Head Nuts
    3. Spark Plug Type Listed Incorrectly in Owner's Manual
    PWC-94-02 Retention of the air Intake Duct Drain Hose
    PWC-94-03 1. Fiberglass Gel Coat Surface Crazing (Spider Webbing)
    2. A Limited Number of 1994 SLTs may need Fiberglass Trimmed from
    the area below the rub rails in the rear corners
    PWC-94-04 Possible Water Leak on SLT Drive Shaft Through-hull Fitting
    PWC-94-05 Engine Cooling Water Inlet Hose
    PWC-94-06 1. Exhaust Manifold Fasteners
    2. Prevention of Water Leakage
    PWC-94-07 1994 SLT Seat and Compartment Door Seals
    PWC-94-08 Front Seat Latch Plate Wear Into Gel Coat on some 1994 SLTs
    PWC-94-09 All 1994 SL650, SL750 & SLT, Fuel Tank Drop Tube Retaining Cap
    PWC-94-10 1994 SL750 Power Trim Nozzle Fasteners
    PWC-94-11 1. 1994 SLT Water Leaks at Steering and Reverse Cable
    2. All 1994 Watercraft. Rear Muffler Bracket may wear through water supply hose
    PWC-94-12 All 1994 Watercraft. Possible water ingestion through the air intake
    PWC-94-13 1994 SLT Fuel Tank Vent Relocation



  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    The pics are of the 650/750 performance Flame Arrestor upgrade from Polaris. Regular Super BN 38mm car gaskets will work.

  7. #7

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    Cool. One of the skis already had the autocock removed, and I pulled the other one out when I installed the new fuel lines. As I said earlier, I had researched thousands of posts and was well aware of the problems they were causing. Hoping to get back to the skis in 3 or 4 weeks, got too much to do right now. 3 cars, 2 generators and a camper A/C sitting in the driveway that people have brought over for me to fix.

    My plans are to check the crank index (since two cylinders were full of gas when we tried to start it), pull and rebuild the carbs, check the reed valves, add the vent to the fuel tank and recheck timing. Sound like a decent plan?

  8. #8
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Sounds good.

  9. #9

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    Oooopppsss

    Well, got started on it. Pulled the carbs, pulled the reeds. The reeds, I believe, have had it. They are not burned, cracked or chipped, but some of them are out to about .035. Book says .015. Some of them are 'bent'. If you hold them up and look down the top edge, they are bowed out at the ends. Is this normal?

    I did a rough check of the crank index with a dial caliper. The index seems to be OK. Then I decided to pull the heads. Dang it. The mag and pto cylinders are running a little bit rich?, but other wise are in great shape. The center cylinder is toast. Very lean? and physical damage is massive. Both the head and piston are pitted and gouged. Some of the gouges are very small in size, but very deep. Maybe 2.5mm long and almost 2mm deep. Looks like somone sharpened up a small flat tip screwdriver and drove it into the head with a 5 lb. hammer. Most of the pits look like miniature craters, very smooth and even. I'm kind of lost on this one. I sure would appreciate some help. I'm good with cars and generators, but 2-strokes are somewhat foreign to me.

    Another thing I noticed is that the water ports in the cylinders and heads had an awful lot of black RTV in them. Is this normal or did the guy I bought them from screw them up?

    I hope the pics are good enough for you. The layout is pto on the left, mag on the right. Thanks.
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  10. #10

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    Also, the piston has scratched the cylinder very badly. Can it just be resleeved, or do I need to repolace the whole jug? The scratches are very deep, I doubt they can be bored out. Can I just rebuild the one cylinder, or is it recommended to do the whole top end? How about a list of places to obtain the parts from, who is reliable?

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