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Thread: Mikuni carbs

  1. #1
    blegan's Avatar
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    Mikuni carbs

    I am rebuilding a rack of mikuni BN 38s, 94 slt750 while cleaning I found defective jet coverblock check valves. The kit doesnt come with that,& Im using genuine mikuni kits. having trouble finding these little boogers. does any one know anything about these?
    Thanks Brian


  2. #2
    Rasta Mon Condoms We Be Jammin!!!!! TxVirageTx's Avatar
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    vlvesa

    get with brian at ultimate watercraft

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    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Mikuni rebuild kits DO have the clear plastic check valves included.

    Read the instructions sheet. It should tell the contents of the kit.
    You need to look for them carefully.

    They often are clung to the instructions from static cling.

    You have to open the rebuild kits carefully because those things are VERY hard to see.

  4. #4
    blegan's Avatar
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    Quote Originally Posted by xlint89 View Post
    Mikuni rebuild kits DO have the clear plastic check valves included.

    Read the instructions sheet. It should tell the contents of the kit.
    You need to look for them carefully.

    They often are clung to the instructions from static cling.

    You have to open the rebuild kits carefully because those things are VERY hard to see.
    different valve ,thanks though the more I get in to this fuel system the more I laugh. weak hoses, a wore out fuel pump,no restrictor ,bad pick up tubes . peices missing in carbs , full of goo ,broken reeds,autocock still in place, no seperator water gas,no in line filter, take vents & valve non existent, base gaskets ripped, I am almost rebuilding fuel sys.completely, Thats all right though Im gaining lots of knowledge.
    Brian
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    It's all good, were learning watching!. And an old ski needs rebuilding anyways, not to mention the auto-cock has to go!

    along with gas tank tubes and whatever else is loose or broken or clogged! good job finding all the bad areas. I'm sure it will run great after the whole system is gone thru. I have a water/fuel separator extra if needed.

    Did you find the screens from the tank tubes yet? there probably on the bottom of the tank. mine were on my 95 slt. but it still ran!. my tank tubes were just nasty looking and bloated.

    Make sure you put the correct length tubes were they go, the reserve is longer than the main feed line. or else you'll have no reserve tank!

    If your going to use a triple pump, Beerdart has the diagram and also remember the restrictor!.(i know you know already),,,and make the pulse line 12 inches or less and keep the pump half way up in the hull or else it could suck up junk oil/gas mess from the case.

  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by blegan View Post
    different valve ,thanks though the more I get in to this fuel system the more I laugh. weak hoses, a wore out fuel pump,no restrictor ,bad pick up tubes . peices missing in carbs , full of goo ,broken reeds,autocock still in place, no seperator water gas,no in line filter, take vents & valve non existent, base gaskets ripped, I am almost rebuilding fuel sys.completely, Thats all right though Im gaining lots of knowledge.
    Brian
    What are you talking about then?




    The only check valve is the clear plastic flap under the jet block.

    Nothing missing in your pic except for the filter.

  7. #7
    blegan's Avatar
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    rebuild

    Thanks for the offer on seperator, but I got one from john zigler that was in great shape & it does have a s.s.mesh filter, and it is going to be completely I dont want to have to fix same problem repeatedly
    Brian

  8. #8
    blegan's Avatar
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    Quote Originally Posted by xlint89 View Post
    What are you talking about then?




    The only check valve is the clear plastic flap under the jet block.

    Nothing missing in your pic except for the filter.
    There were some circle valves of some sort. You are exactly correct about it being the flap under block. sorry about confusion these are the first carbs that Ive rebuilt. I appreciate your help & patience.
    Thanks Brian

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    The circle valves are for the internal fuel pump for the 44mm's. They are exactly the same design as the external fuel pumps, but only a smaller version and integrated into the carb body.

    It's actually a really cool and simple design.

    Vaccum and pressure are applied to a plastic diaphragm inside the fuel pump through the pulse hose. (piston going up or down dictates + or - pressure)

    That movement of the diaphragm draws fuel through the first check valve which seals shut, on the - pull. Then forces the fuel through the second check valve on the + to feed the carbs. This happens every full revolution of the PTO cylinder because that's where the pulse fitting is. This is why you need to have good compression on the PTO cylinder, or your fuel pump will not be as strong as it should.

    The restrictor is needed to provide some resistance against the fuel pump to create fuel pressure. You need fuel pressure to help supply the carbs when running at WOT and the most fuel is needed.


  10. #10
    blegan's Avatar
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    finally figured it out

    Quote Originally Posted by xlint89 View Post
    The circle valves are for the internal fuel pump for the 44mm's. They are exactly the same design as the external fuel pumps, but only a smaller version and integrated into the carb body.

    It's actually a really cool and simple design.

    Vaccum and pressure are applied to a plastic diaphragm inside the fuel pump through the pulse hose. (piston going up or down dictates + or - pressure)

    That movement of the diaphragm draws fuel through the first check valve which seals shut, on the - pull. Then forces the fuel through the second check valve on the + to feed the carbs. This happens every full revolution of the PTO cylinder because that's where the pulse fitting is. This is why you need to have good compression on the PTO cylinder, or your fuel pump will not be as strong as it should.

    The restrictor is needed to provide some resistance against the fuel pump to create fuel pressure. You need fuel pressure to help supply the carbs when running at WOT and the most fuel is needed.

    AFTER PUTTING MY GLASSES ON & REALLY LOOKED AT DIAGRAM, i WAS ABLE TO GET PAST BEING CONFUSED, AND YES FOR A RESTRICTOR I HAVE A BRASS 1/4 BARBED CONNECTOR TAPPED TO SUGGESTED SIZE & A # 90 MAIN JET ABOUT 3 IN. PAST FUEL RETURN AT RACK.I ALSO HAVE A MIKUNI 3 OUTLET FUEL PUMP
    THANKS AGAIN BRIAN
    Last edited by blegan; 02-27-2010 at 12:15 PM. Reason: NOT DONE

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