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  1. #1

    Breaking Gp1200r Speed Record NO Overbore

    Hello everyone!

    So like it says in the title, I'm looking to break the speed record without over boring the cylinders to 1390. I will list what I have, and I am hoping I can get some help from people who know what they're doing, or if I can have phone numbers of people who DO know what they are doing. Heres what I know I have:

    Rebuilt top end (wiseco sleeves, pistons)
    RIVA head w/ 41CC domes, 3 separate heads (135PSI across the board)
    Solas (13/19) impeller
    RIVA pump cone
    Riva Intake grate
    Riva Rideplate
    Impeller housing w/ plastic wear ring (better seal)
    Stinger 3 exhaust w/ extra pisser mounted on rear
    Riva Flame Arresters
    VF3 reeds
    Riva nozzle(not sure what type, exactly)
    Riva sponsons
    Used to have riva comp, blew up on me. Stock Comp as of now.

    My carbs are currently stock
    117.5 mains
    95 pilot
    1.2 n/s
    75PSI pop-off

    I want to get every mph out of this, part of a bet. Is there any way to trick the computer out of the rev limiter?

    Also, I would like to rejet my carbs as necessary. If someone could give me all of the sizes the recommend, pop-off, and high+low adjustments, I would love you!
    I know I'm not very far off, because all thats left is the carb! Maybe one day I'll get a triple pipe, but I want it to be reliable as well.

    If anyone can give me any more tips or tricks to how to make this ski go FAST, I would really appreciate it!
    BTW, my goal(shooting high) is 85 MPH on glass water.

  2. #2
    powerstroke specialist mikegp's Avatar
    Join Date
    Mar 2011
    85 is never going to happen unless you run triple pipes, on the other hand my own opinon , i will increase comp at list to 150, also i saw a advent ecu on ebay a week ago.

  3. #3
    The ECU I know only changes the rev limit. Is there a way to put a kind of false readout onto the tacho going to the computer to decrease RPM to just the right amount? A resistor of some sorts? This would surely bypass the computer greatly. And as far as I know, 86 is possible without triple pipes. 86-90 is where the triple pipes and overbore are a must.
    Let me know guys, I want to win this bet. Im no novice to mechanical/electrical, so shoot me ideas and I'll consider and try them!

    PS. I have a friend who is running 94 GPS on his gp1200r, just needs to get the speed confirmed. I'm looking towards those kinds of numbers.

  4. #4

    Join Date
    Jun 2014
    MS Gulf Coast/Abbeville, LA
    your friend with the gp1200r isnt in biloxi MS is he?

  5. #5
    Nope! He is in florida. He said running 80 maybe is something special in Jersey but its commonplace in florida

  6. #6
    Altezza01's Avatar
    Join Date
    Jun 2007
    Destin, FL
    There's a few things that I see wrong with your setup right off the bat that will have to be changed.....
    1200cc will need to be 1300cc
    135 psi head won't cut it.
    Flame arresters are gonna have to be swapped out with something like Ross nemo tb's.
    The stinger is only good on holeshot and will kill top end.
    that prop is way too small.
    You'll have to run a 800 intake grate.
    That ride plate needs to be modified by Jim's performance.
    The riva sponsons are only good for turning. Ditch them for oem stepped sponsons.
    You're also going to need porting.

    Even with all the correct mods and hull setup you'll most likely be yielding 80-82.

    You should look at the 2 stroke speed data base and see where other skis stand.

  7. #7

    Join Date
    Aug 2006
    You are not going to go past the stock rev limiter range with a stock ported engine unless you got triple pipes, or underprop it which will slow you down. The tach gets it signal FROM the CDI, which is where the rev limiter is located, internally.
    You can get to 70-71 with proper carb jetting, flame arrestors, 150 psi compression, fast ride plate and good boat setup. Another 10 mph is a tall order on a stock bore even with porting.

  8. #8
    I can do most of the modifications myself. Modified how exactly? I know that trimming the edge of the plate out 5 degrees will give about a .7 to 1 mph gain. The 1300cc isnt possible, hence the without overbore(will only add 4 mph anyway). What size domes do you recommend, what fuel? How should i bend the prop/what should I replace to?
    I heard the 800 is prone to failure, hence why i got 1200. Its a loss of 1mph i know, but Id prefer to keep my grate, or cut it/bend slightly. I think I'm going to manufacture my own sponsons, something more hydrodynamic while still having grab. I care about HIGH, not low. The sponsons are practically out of the water on glass anyway, so not an issue with top end. I've seen the database, and showed it to my friend, and he said those are all poor numbers. The flame arresters are easy to get, might upgrade to that.Stinger - i know its no good for top end, but compared to stock which adds a solid 10 lbs its an improvement. Triple pipe is out of the question at the moment!

    I've seen this ski go 90.2 without a triple pipe, although it was a 1390. My friend told me that 190 CCs will only give you another 4-5 mph being useful only past 86 mph, so if you ran 86 with 1200, youll run 90-91 with 1390, and 92-93 with the triple pipe.

    I still need info on the carbs though! The engine is half the story, the carbs are the other half thats a pain in the a$$.

    Thanks for all the help guys!

    Like i said, I'm out to win a bet. I'll do anything to actually get to the numbers I want.

  9. #9
    Altezza01's Avatar
    Join Date
    Jun 2007
    Destin, FL
    I think you need to do more research on mods and how much speed you gain from them. Being a 1200 I say you won't even hit 77 mph. I'm guessing more like 73-74.

  10. #10
    I've successfully hit 76 with mods on there right now. My question, will rejetting carbs allow better breathing?

    Also, I need something for the rev limiter. I know there is a bypass I just dont know exactly what is needed.

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