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  1. #1
    Join Date
    Oct 2006

    installing a big bore kit on a stock gpr1200


    just wondering how much work and modding is invloved in installing a ported big bore kit on a stock GP1200R (02).

    I found what looks like a reasonably perfect condition kit for sale somewhere and I am looking to add more power to my existing setup.

    I have a 13/19 prop not yet installed and have ordered a polate from Jim as of yesterday but I am wondering if it is worth the time and money to invest in this kit I found.

    It contains the following.

    complete 1390 top end kit ported by Lowell Hourning includeing gaskets

    the piston are GroupK

    porting all cyl.
    boreing & plateing all cyl.
    cutting head

    gas valve conversion kit

    3 balanced GroupK pistons

    3 oem wrist pin bearings

    3 oem wrist pins

    3 cylinder base gaskets

    3 power valve base gaskets

    exhaust manifold gasket

    oem bored to 87mm head gasket

    what sort of gains would i get installing something like this and what else would i have to get to make it work if anything?>

    I am struggling to find a decent workshop here in Sydney Australia that does this sort of thing at the moment so if anyone can make a reccomendation in this area please let me know, we are kinda starved here for this sort of thing.

  2. #2
    Me Hahn and Joe H204YOU's Avatar
    Join Date
    Jan 2006
    Panama City Beach Florida
    First thing would be to find out if the porting is for single or tripple pipes
    Well after noticing it has an exhaust gasket its probably single pipe porting,but I would say if your not real familiar with the GPR plateform you might have youre hands full jetting and getting it dialed in.IMHO I would shy away unless its a steal deal.
    Last edited by H204YOU; 07-05-2007 at 07:56 PM.

  3. #3
    Join Date
    Oct 2006
    whats a kit like that worth?

  4. #4
    spud's Avatar
    Join Date
    Jul 2006
    Oceanside, California
    Its a single pipe. Call Lowell and ask him about the jetting. Ask him if the pistons have been coated. How many hours are on your crank? You should have a trued and welded crank to play it safe.

    That is a great deal on the parts listed. You will need to get an aftermarket ignition high pressure pump and a custom dynafly impeller. Lowell will suggest the proper pitch. V-Force 3's work well with that engine too. Lowell does first class work and that engine will scream

    So once you get the engine kit you will need to invest about 1500 more to bring the ski to its potential.

    Jim can give you advice on trim tabs.

  5. #5

    Join Date
    Nov 2005
    North East Mo

    I am who is trying to sell it the link above should give a little more history then what I listed on Ebay
    I will try to give more detail about this motor and it history.
    It was originally created by Lowell for Scott as a 1400 tripple piper with pinned gas valves, Scott changed his mind and decided to go with a single pipe after all. (now on a pinned valve engine you don't raise the port height as you would on a working valve motor so you don't lose the low end power)
    Well in the process of things Scott took his boat down to Kerry.
    Kerry raises the port height up were it belong to make power with a single pipe, now you got a motor with a soft bottum end that starts comeing in hard at 4500 RPM.
    The crank let losse and destroys one cylinder and Scott sell the boat to me blown up, I send the motor out to Lowell and he frees the power valves and makes up another cylinder and hones the other two.
    So here we are is a Kerry motor or Lowell Hourning?
    What is it worth? You decide I paid Lowell $1397. for all is machine & port work and the GroupK pistons and some of the gaskets bearings and stuff. That does NOT! include the gas valves or figure in for the head and the core cylinder and a few other gaskets.

    The above why I try to get people to call me I don't like to typeing

    this is 11:40 pm and I need to go to work
    I will check back in the evening.

    There are tunner on this board that forgot more about jetski then I will ever know and are better qualified at anwsering your question then me.

    I am trying to be straight forward with what I got.
    Cell 660 988 2085

  6. #6
    just GOT TO DO IT! great lakes gpr 1200's Avatar
    Join Date
    May 2006
    muskegon michigan


    If you are not really into screwing around and screwing around with jetting and getting the impeller right.

    AND You want the power.... buy one from group k or lowell as a kit.. they will have it all ready for you. I bought the group k kit and it is great for lack of screwing around (the others may be too , But I have never had one so of those I do not know). you get the group k kit and bolt it on... all done.... break it in.... ride like hell!

  7. #7
    Join Date
    Oct 2006
    After speaking with Todd at a local place here I am having second thoughts about going big bore.

    I knew i was going to be due to for top end rebuild and so thats going to be first up before it spitts a piston out as it has 120 odd hours on it so far and when i bought it back home the other week it did not sound at all good

    mental note: never let freinds borrow your ski, i swear it was running OK last time i used it but i know its been used by someone else since then.

    I am looking at a few different mods atm and will make a decision of how to spend my allocated budget over the next few weeks. Unfortunatley for me there is no point in building a ski for glass conditions as it is something that I only see first thing each morning as I do not do any lake riding, its all open water so I need to keep that in mind ( wish i had known that before I ordered a plate from jim doh).

    anyway i guess i am going to have to find out the hard way like everyone else and learn slowly but surley what works for me and what does not.

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