New sbt 657 running lean
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  1. #1
    PWCToday Regular
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    New sbt 657 running lean

    I had a crankshaft bearing go on my old motor which took out the rotary valve shaft, brass gear and the gear on the crankshaft. So I decided to get a "new" sbt motor. The old motor was running great until the bearing gave out. So when I took the only motor out I made marks on the stator and housing. The stator was turned all the way to the right ( timing retarded as much as possible)When I got the new I put the stator back on same position as old motor. And put everything back on and installed the motor. I followed the break in guide line with the 32-1 fuel and the 1/4 and half throttle deal. Once I got to half throttle I started noticing a little of a knocking noise when I would let off the throttle. Didnt think it sounded quite right but it concerned me a bit. When I got above 1/2 throttle I started to notice a ping noise every now an then. When I heard this I put the boat back on the trailer. I was out again today with new plugs and ran 3/4 throttle heard a few pings killed the motor and looked at plugs. They were very dry. So I figure I'm either running lean or spark timings off. My question is where do I look first? My spark timing shouldn't be off as its retarted as far as it can go. Can being a few degrees off on the rotory valve timing cause a lean condition? The throttle feels pretty normal. Should I look at the carbs, fuel pump and filters. I dont know where to start looking. Any help would be greatly appreciated. I do t want to blow up a new motor.

  2. #2
    PWCToday.com Is My Home Away From Home Bionic racing's Avatar
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    Re: New sbt 657 running lean

    Why did you retard the base timing ?

  3. #3
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    Re: New sbt 657 running lean

    Quote Originally Posted by Bionic racing View Post
    Why did you retard the base timing ?
    That's how it was on the the one the bearing went bad on.

  4. #4
    PWCToday.com Is My Home Away From Home Bionic racing's Avatar
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    Re: New sbt 657 running lean

    Five or four wire stator ? Lookin at stator , from the front of engine , rotated it clockwise or counter clockwise ?

  5. #5
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    Re: New sbt 657 running lean

    Quote Originally Posted by Bionic racing View Post
    Five or four wire stator ? Lookin at stator , from the front of engine , rotated it clockwise or counter clockwise ?
    5 wires rotated clockwise.

  6. #6
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    Re: New sbt 657 running lean

    I checked the carb filter and there was some debris in it but nothing crazy. I went out yesterday and messed with the low and high speed jet. That did not do anything to help with the ping and lean condition. It only took about 1 min for the plugs to be to hot to touch Today I rotated the stator counter clockwise and plan on going out tomorrow to see if that does anything. My question is can rotary valve timing being off cause a lean condition? I have carb rebuild kits on the way but I don't think thats the issue.

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