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  1. #1

    Jetting Help Please

    Okay guys, just got done rebuilding the engine in my Gp1200r. New crank, New cylinder, Yada Yada. Engine is solid.

    Took it out last weekend. Ran great at WOT, very fat in the mid range. Pulled the carbs, double checked and made sure everything is at the same settings as before the motor blew. Took it out this weekend again, still super rich.

    Have to sit and chop the throttle multiple times before it picks up and goes.

    I'm running at 6500' elevation. Stock ski. Running 95 pilot, 117.5 main, 1 turn out low speed, 1.25 turns out high speed. 115g (gold spring), 1.2 needle/seat. Ski ran great before I lost a piston.

    Ideas for next things to check? I have pretty much no idea.


  2. #2
    Forgot to add. Stock airbox. Not too interested in going with aftermarket f/a's yet.

  3. #3
    I guess I should have also added that I rebuilt the carbs when I did the motor. Added t handles to the high and lows and did the balanced return mod with a 95 jet.

  4. #4
    I guess what I am getting at is that the adjusters are all in their pre-overhaul positions and I didn't touch any of the jets. So, aside from the fact that I rebuilt the carbs and did the balanced return mod, nothing is hardly any different than it was before the engine overhaul.

    Does the balanced return mod affect jetting at all? I was led to believe it didnt?

    Would installing a gasket wrong or some other assembly problem cause this issue? I didn't actually know the check valves had a concavity to them, so it's entirely possible I put one of those in wrong. However, my understanding is that the balanced return mod would make this unlikely to be a problem.

  5. #5
    Okay, had some time to tear into the carbs tonight. Upon initial disassembly, didn't see anything disconcerting. Checked the pop off pressures. Good news, bad news kinda deal.

    Good news, they were all within a psi or so of each other. Bad news, that pressure would be 90 psi.

    I've never heard of that high. Would that cause the issue?

    I thought I read it was supposed to be 65-75 psi on a bone stock Gp1200r.

    I also found a pump housing gasket that was backwards and bleeding pressure bad. Fixed that.

    Any ideas where to go from here?

  6. #6
    Well apparently it's not out of the ordinary to be that high. I found an old post from OSB where he said 1.2 N/S with 115g springs will give 90 psi or so on a stock gp1200r.

    So I guess now the question is would a leaking pump gasket cause the issues I was describing?

    I'm starting to wonder if I was lean and not rich. Lucky if I was.

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