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  1. #1

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    1200 XLT dropping #1 cyl when on plane

    1200 XLL/XLT with an issue where it drops #1 cyl when coming on plane, takes off great then bogs a bit from losing #1. I have done many things with Yamaha's but have an issue now that is kicking my butt. 99 XLL, rebuilt by me including carbs and restrictor mod, ran 60 last summer until a no start in Aug. Found it was a bad CDI so it sat until winter. Bought a used CDI from I think someone on here and installed, started and sounded great. When put on water however, will start fine at full throttle then #1 cyl drops out. Replaced plug, checked spark, looked good so figured carb filter plugged from sitting with no stabil. Pulled carbs, no issues, went ahead and rejetted/FA's, pop off adjusted, changed fuel pump checks, ect like my other boats. Does not have a fuel switch, line runs straight thru filter then to carbs. Vent check valve switched out. No flapper in tank. Original lines. Sounds great on trailer but same crap on water. Pulled return line, fuel is coming out when running, but sounds/feels like running low on fuel and #1 cyl is last to get fuel cause its at end of line. Thinking maybe the used CDI was bad on #1 output swapped CDI with my other boat, no change. Temp and cat sensors check perfect, but how does limp mode work, just cut one cyl? Thing is runs well and snappy rev on trailer, and #1 cyl hot, but when on water for a few min #1 is cold. Any other ideas? Oh yeah, swapped out coil and plug wire too. Compression and reeds good.

    It has original Yamaha fuel lines, have anyone seen then go bad inside? Never had any issues in any other boats with Yamaha lines.
    Last edited by LT1GMC; 07-06-2014 at 04:19 PM.


  2. #2

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    Even though you went through carbs a while back you need to re check the small fuel filter inside each carb for trash on the fuel pump side. I have seen them get clogged pretty easy since they are so fine of filter in just a matter of weeks. and skis will run good at low rpms but when at wfo one carb can starve for fuel. Even if you have fuel returning to the tank they can still be clogged. Tommy Jordan

  3. #3

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    Thanks Tommy, but I just pulled them this week, the middle one had some of the gummy/sandy like stuff in the filter, but everything else was good. Changed the jetting/pop-off, removed accell pumps and added F/A while I had it apart.
    Quote Originally Posted by 2fast4u View Post
    Even though you went through carbs a while back you need to re check the small fuel filter inside each carb for trash on the fuel pump side. I have seen them get clogged pretty easy since they are so fine of filter in just a matter of weeks. and skis will run good at low rpms but when at wfo one carb can starve for fuel. Even if you have fuel returning to the tank they can still be clogged. Tommy Jordan

  4. #4
    Highlifeking's Avatar
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    Purhaps the powervalve on that cylinder is not operating- When the valve is closed you have bottom end, but if it wont open your top end will be lacking. Just a thought

  5. #5

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    Pulled cover on PV, working fine, actually checked that valve itself still was connected to its shaft. Ran new parallel fuel line and tee'd in supply between 1 and 2. No help.

  6. #6

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    Got it home and checked compression, 145-150 all cyl.

  7. #7
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    sounding like a case leak..everything else seems to be covered. might be easier to try another rack of carbs then to hunt down a case leak..just to narrow the scope a bit more.

  8. #8

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    Leak checked, none. Spark will jump 1/2" gap at 6000 on home made tester.
    Pulled #1 carb and FOUND THE PROBLEM! Since I had rebuilt carbs a couple of years ago, when I pulled them a couple of weeks ago tracking this problem I cleaned junk in #2 carb filter, cleaned pumps and checked check valves on all, installed new jets, and adjusted pop off. Did not pull needle and seats out, as they were new 2 yrs ago. So when I pulled the N/S today I found 3 chunks of metal like corrosion plugging up # 1 N/S on the bottom side. Let just enough fuel thru to idle but not rev when loaded. Sure cost me alot of time and trouble. Good lesson for all.

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