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  1. #1
    Buplaux's Avatar
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    Feb 2014
    Zionsville, IN

    why does two identicle gp1200r with same carb setting have differnt a/f ratio

    Join DateZionsville, IN

    Help with Identicle gp1200r skis with same carb setting but different a/f ratios?

    First post*i have pair 2000 gp1200r i purchased this winter for a project. 80 hrs on both. One lost oil line with previous owner so i completely rebuilt that one. Both went to premix, both have had carb return mod done, all carbs have been completly rebuilt with mikuni parts, stock air box and jetting and d-plate in both. Compression on both skis was good and even across the board (original one was a little lower than rebuit ski but to be expected). Both skis run flawlessly with no bogging or dead spots anywhere in throttle range. Here is my question.. Why does original engine run leaner (according to the plug chop) than the rebuilt engine with carb settings exactly the same? I realize small crank seal leak could be possible but the plugs are all exactly same for all three cyl. Figured they would be diff according to where leak in relation to cylinder may be if that was the case? I set needle arms correct height and kept original springs in all carbs. I dont know pop off but should be somewhat irrelevant because wot plug chop shows same results. Could it be simply because the compression is lower on this ski the pulse is effecting fuel pressure and also a/f ratio? It isnt lean to where i will melt (very light tan) anything but for sure leaner than the chocolate colored plugs on the rebuilt engine. Thoughts on why the difference?
    Thanks, Jeff

  2. #2
    Bad main seals?

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