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  1. #1

    Gp1200 Non-PV Jetting

    I just put my ski together for the first time yesterday. It starts and runs alright but i'm wondering if i need to change the jetting from stock. Here is the list of aftermarket and modified parts on the motor:

    K&N Air Filters
    Filter adapters
    Choke plate block off plugs
    Primer kit
    Premix @ 32:1 ( for break in . Plan on going to 50:1 )
    Maxima 927 castor two stroke oil
    Very conservative porting on the cyl jugs by Jim Sechler ( Hydroplane racer )
    Cyl's bored to 84.5mm
    Prox Pistons

    Not sure on the exhaust pipe it may be an 1100 exhaust pipeClick image for larger version. 

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    Here are some pictures of the motor outside and inside the ski


  2. #2
    Yamaha artisan Cutlass's Avatar
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    Yes you need to make some changes. But it really depends on the porting job. If the ports have not been raised or lowered (ie just "cleaned up"), the following recommendation from a previous post I made, might work or get you close.

    A stock/mostly stock engine GP1200 with flame arrestors and premix, should use the 115 gram spring with the 1.5 NS to get a pop off of around 50 to 55 psi. the pilots jets should be 100 across all 3 carbs and the highs should all be the stock 135.
    Run the low speed screws all at 1 1/4 out and the highs at 1 1/2 out.
    Thats exactly how I run mine and it runs perfect. My minor mods are: chokes removed, flame arrestors, .5mm overbore, very minor case porting/clean up. I run oil injection. Mine runs rich, but not rich enough to give me any problems. Your premix gas will slightly lean out the A/F ratio but should still be very safe. Do some minor adjustment if you feel you need to.

  3. #3
    Thank you Cutlass !

    I do not own a pop off gauge. What Kind of jetting do you recommend for roughly 750 ft and premix at 50:1 ? Here are the plugs from 6 gallons of fuel during breakin at 32:1.Click image for larger version. 

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  4. #4
    Yamaha artisan Cutlass's Avatar
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    750 foot above sea level? Same. 750 isn't high enough to warrant anything different. if said 3000 or 5000, then I'd start thinking about different jets.

  5. #5
    Yamaha artisan Cutlass's Avatar
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    Do you have any specific details about the porting job done to your cylinders? That could really affect the jetting needs. Maybe the person who ported it has a recommended jetting?

  6. #6
    Ill get some more info on the porting. Currently Jim is out of the country on business. I ran it today with the main screws pulled out to two turns at 50:1 fuel ratio and ran a 58.8 on the GPS. Im going to pull the plugs when the motor is completely cool in the morning. I also keep blowing the first hose clamp off the U pipe boot. Im thinking there is too much pressure under that rubber boot and its moving the hose clamps off. Any ideas?

  7. #7
    Yamaha artisan Cutlass's Avatar
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    I've never heard of anyone having that problem. I doubt its too much pressure. Maybe something is misaligned or the pipe is greasy and allowing the boot to slide off

  8. #8
    The hose clamps are on as tight as i can get them with a 1/4th inch ratchet without breaking the rubber and it pushes the hose clamp off the front every time I run it hard. Also I clean everything off with brake cleaner before I put it together and it keeps pushing the hose clamp off. The 1/2 line that runs off the top of the expansion chamber is reduced to 3/8. I have 2 water outbounds besides the stock ones. One off the front of the head and one off the center cyl. Im going to try to put a pisser off the rear cyl hose too try to alleviate some of the pressure to the boot and see if that helps.

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