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  1. #1

    GP1200R Running Rich after Carb Rebuild

    I've been late in posting this, but better late than never...

    During the off-season last year, I took the opportunity to rebuild the carbs in my 2000 GP1200R. I followed OSB's recipe EXACTLY. I installed aftermarket F/A's (chokes intact) and followed his exact specifications including both jets and adjuster turns and disabling the accel pump. I also did the common return mod and added a primer. Oh, and I installed a holeshot kit at the same time.

    I knew that because of my altitude (6000' ASL), I was likely to be rich. I asked for advice on adjustments here in this forum and no one replied. So instead of modifying OSB's recipe, I just decided to follow it knowing that I could be rich and adjust from there. After all, it's better to be rich than lean, right.

    Fast forward to the maiden voyage with the new carbs. It was awful. The ski was next to impossible to start and would die unless you sat and played with the throttle. It wouldn't get out of its own way when accelerating and you basically had to chop the throttle until it got up enough in RPM to take off. Even then, performance was poor. According to the dream-o-meter, I lost approximately 11 MPH in top speed from before the carb mods. The death knell came when my wife decided to take it out with her dad on the XL800. About half an hour later, I saw them off in the distance, him towing her. It died on her and she ran the battery dead trying to restart it. The ski hasn't been back out since because I haven't had time to play with it.

    I am thinking that I am very, very rich. Is this behavior consistent with running rich? If so, what should I start adjusting first and how much?

    I am probably going to make this a winter project. I am dreading taking that damned exhaust out again.

    EDIT: The engine already had the d-plate and chip before this project was ever undertaken.


  2. #2
    Ignition chop and read the plugs? Only way to know if your in the ballpark.

  3. #3
    Quote Originally Posted by Cat Tech View Post
    Ignition chop and read the plugs? Only way to know if your in the ballpark.
    Can you noob it down for me?

  4. #4
    Quote Originally Posted by Cat Tech View Post
    Ignition chop and read the plugs? Only way to know if your in the ballpark.
    And let's say for the sake of argument that I am rich. In what order would you start adjusting things (jets versus adjusters)?

  5. #5
    So I bought one of those Mikuni slider calculator things off Amazon. I haven't received it yet but from looking at the pictures it looks like 6000 feet means I need to go down 7.5 jet sizes on the main jet. That's wild.

    Question - would you think I would need to make a similar reduction on the pilot jet?

  6. #6
    Myself's Avatar
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    With starting and idling issues the main jet is not in the circuit so, yes, the pilot would also be very rich. Let's see a good pic of your spark plugs.

  7. #7
    Quote Originally Posted by Myself View Post
    With starting and idling issues the main jet is not in the circuit so, yes, the pilot would also be very rich. Let's see a good pic of your spark plugs.
    Finally got home. See attached. Click image for larger version. 

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  8. #8
    I had that problem on a ski and it was jetting

  9. #9
    Myself's Avatar
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    Those plugs look overall terrible. Also don't waste any more money on those E3's. If you want some better plugs try Iridium. The center plug also has no color around the thread ends. Possibly WAY rich or maybe a firing issue on that cylinder. Put in new plugs and fire it off. After we know it will run remove all plug wires. Then put on only one and try starting it. It should start and run on any one cylinder. If you have a no spark on one cylinder the whole thing will run crappy and appear to be very rich as the unspent fuel will be sucked back into adjacent cylinders during exhaust pulse pressure wave return.

  10. #10
    Quote Originally Posted by Myself View Post
    Those plugs look overall terrible. Also don't waste any more money on those E3's. If you want some better plugs try Iridium. The center plug also has no color around the thread ends. Possibly WAY rich or maybe a firing issue on that cylinder. Put in new plugs and fire it off. After we know it will run remove all plug wires. Then put on only one and try starting it. It should start and run on any one cylinder. If you have a no spark on one cylinder the whole thing will run crappy and appear to be very rich as the unspent fuel will be sucked back into adjacent cylinders during exhaust pulse pressure wave return.
    Thanks.

    The E3's were purchased during a sale. With instant rebate, they were about the same cost as NGK's. I don't spend money on spark plugs, they're all a gimmick. I prefer champion coppers myself.

    The ski will run, if that's what you're asking. I just blew it out for winter, so I started it like 5 days ago.

    Hadn't thought about running it on one cylinder. I don't believe I have anything mechanical going on in a single cylinder. The engine is solid mechanically, it was just rebuilt.

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