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  1. #1

    Yamaha SUV non-PV 3 cylinder with the top speed of a 2 cylinder????

    Posting this for a friend who has an SUV as well.

    99 Stock 1200 non-pv with rebuilt SBT...

    Setup: Rebuilt carbs (not sure if they are SBT kits or Mikuni but no leaks), compression checks out good at 120 across all 3, wear ring clnc. is .35mm so not bad at all for spec if memory. Carbs NOT checked for popoff yet but they were out of adjustment on the highs and low speed screws.

    His problem: He has a little low throttle bog but the main issue that we are trying to figure out is why he can only get it to 36mph at WOT when it should be doing in the low 50's like the rest of our skis.

    Is it possible that simply the high speed screw settings are not allowing him to achieve high end speed? I guess if they were turned in almost all the way that they would not allow enough fuel to pass right? The other carb possibility is that he does not know if the guy who cleaned them realized that the smaller jets in the carbs were staggered sizes. He may have mixed them up. The obvious solution is to pull them and take a look (and we will do this), I am just wondering if something so simple could cause a low-top end condition?

    Aside from that...any suggestions on where to look? Malfunctioning fuel pump on 1 cylinder causing only 2 to push?

  2. #2

    Join Date
    Aug 2006
    Sounds like one cyl not participating. You may want to check temps next to each cyl to see which one is weak. I worked on a 1100 venture one time that had a broken wire on a stator coil. It was broken inside the insulation, you could not see it, but when you pulled the wire it stretched. That boat had a light miss, and low top speed was the result. Another boat, a Superjet, had a broken down plug wire, it had burned the wire apart about 3" down from the coil. You could not tell from outside, but the wire was broken inside the insulation. It would run at dle, but cut out under load(higher voltage required to fire the plug when under load).
    Everybody looks at the carbs nowdays because bad fuel and etc. make them the #1 suspect, but don't forget the other things needed. Compression, spark, good reeds, no air leaks, fuel.

  3. #3
    Good Compression...check
    The rest...?

    Good read. I would have never thought about the wires in a million years. Sure does sound like a soldier down though with nearly exactly 2/3 of the speed I would expect out of his ski.

  4. #4

    Join Date
    Jul 2010
    Check if all the cylinder is working by running it till warm up and feel the cylinder. I used to have the polaris that only use 2 cylinders due to bad spark cable.

  5. #5
    what is the indication?that the non firing cylinder gets hot or is colder than the rest? since he does prexmix and has good compression i suppose thy symptom would be a hot cylinder if it is not getting fuel to lube it and if there is no spark it would be i guess one real simple thing he should do is put e fresh plugs in just in case there is a possibility of a bad spark plug?

  6. #6

    Join Date
    Jul 2010
    no spark = cool cylinder, the heat is generated by the burning of the fuel not by the friction of the ring against cylinder wall. if spark plug problem, then fuel still get into the cylinder and lube it, just not burning to generate power. Temperture feeling is just a quick test if you have no other tool with you. For me, i use the spark plug tester to test the spark.

    From there you check backward, the CDI, the the stator. For my SUV it was the stator, I got one very heap from a nice member here

  7. #7
    while helping my bud with this issue i took mine out to test it with fresh carbs to check them out. got the lidle adjusted under load with the tiny tach and the low end adjusted with the low screws. then, i couldnt get it up to speeds past thirty five...number keys not working on this cell phone i am using...

    it finally hit me. that damn sbt primer that i installed on the primer line is the cause. when i have the fuel selector in the prime position...the inline primer tee is too restrictive to allow proper fuel flow at wot. as soon as i put the selector in ... on ... it rocks and rolls. i bet him the first two rounds that this is his problem. he sent me a text saying they installed his primer tee after the fuel selector on the inbound side of the carb rack. he will reconfigure this and give er a try. will report back.

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