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  1. #1
    Mongoose's Avatar
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    Big bore 800pv carb help please!!

    Hi,
    I am thinking of buying a big bore (groupk) top end with working powervalves from a good forum member, but I am struggling with the carbs.
    I need to stay with the stockers as I can't afford aftermarket ones at the moment.
    Are the oems ok for this top end?/(I assume yes because groupk use them on the 3 cyl)
    Where do I start with jetting? I havent got a clue, and I don't want to seize it!
    Do I leave the choke plates in?
    Do I run aftermarket FA's?
    Groupk not really interested as I don't live in the States. (Or I was unlucky and talked to the wrong person when I rang!)
    Any help would be great as Scittb is waiting for some money!!


  2. #2

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    Cool

    on the I series carb's group K always seem to leave choke plates in (suppose to be better signal @ 3/4 throttle)
    as for jetting how big is there big bore-most likely same piston were using for 1390 so you could that to start just set up FAT and go from there
    I tired to find the factory pipe jetting for there twin pipe set up,seem not made any more and jetting spec. are gone from there site

    later cd

  3. #3
    Moderator OsideBill's Avatar
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    GroupK also runs stock air box and stock jetting with adjustments to the screws only. I have found through talking to members here and doing a couple sets of these that the following jetting works well on the triple GK 1390's with aftermarket F/A's installed.

    120 Pilot Jet
    140 main Jet
    2.0 N&S
    Black 80gr Spring
    Start at 1-1/2 turns out on all screws and tune from there.

  4. #4
    Moderator OsideBill's Avatar
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    Quote Originally Posted by chip View Post
    on the I series carb's group K always seem to leave choke plates in (suppose to be better signal @ 3/4 throttle)
    as for jetting how big is there big bore-most likely same piston were using for 1390 so you could that to start just set up FAT and go from there
    I tired to find the factory pipe jetting for there twin pipe set up,seem not made any more and jetting spec. are gone from there site

    later cd
    CD here is a copy of those specs from FPP
    Attached Files Attached Files

  5. #5
    Mongoose's Avatar
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    Quote Originally Posted by OsideBill View Post
    GroupK also runs stock air box and stock jetting with adjustments to the screws only. I have found through talking to members here and doing a couple sets of these that the following jetting works well on the triple GK 1390's with aftermarket F/A's installed.

    120 Pilot Jet
    140 main Jet
    2.0 N&S
    Black 80gr Spring
    Start at 1-1/2 turns out on all screws and tune from there.
    Thanks Bill,
    That's exactly what I needed!
    Might get you to work on the stockers for me.

  6. #6
    quadzilla's Avatar
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    Cool Jetting..

    Hey Mr Mongoose..

    Congrat's on the top end..!!

    Think you'll find its not Group-K but infact a Lowell top end..

    Jetting will be a little bit different..

    Bill Is your Guy here..!!

    That topend on a WB3 will be something else..

    Gerry

  7. #7
    Check your PM's
    Thanks
    Scott

  8. #8
    Moderator OsideBill's Avatar
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    If it is Scott's Lowell top end, then yes it will be different jetting.

  9. #9

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    Cool

    Quote Originally Posted by OsideBill View Post
    CD here is a copy of those specs from FPP
    thanks mr bill

    later cd

  10. #10
    Mongoose's Avatar
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    Ok, It looks like it's Lowells work.
    What about jetting for that?
    How does it differ from groupK's -Im assuming Lowell uses group k's pistons-Is the porting more aggresive/comp higher etc?
    Also can somebody send me the instructions for grinding the cases please?

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