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  1. #1
    cyrillefrenchy's Avatar
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    yamaha high pop off pressure

    hello carb experts, I noticed after rebuilding a few sets of carbs some have pretty high pop off pressure , like 60/65 psi+, should I leave em like that or try to lower pop off pressure around 45psi or less, we are talking about all stock engines.
    thanks


  2. #2
    What motor? If this happens to be a 65U, one of the gurus recommends a 55 psi popoff. Need to know what motor if it isnt the 65u

  3. #3

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    I was always under the impression that the PWC manufactures began running high(er) pop off pressures because the EPA would rate their emmisions somewhere at 3/4 throttle. A high pop off pressure ensures that the engine runs lean at 3/4 throttle and puts out the least emissions yet still runs safely. But with a little time and a dirty/partially plugged carburetor you can be subjected to a seized cylinder caused in the mid range.

    I've also read that a higher pop off pressure aids in low end tuning because it is more difficult for the needle and seats to leak. 3 cylinder engines vibrate a lot and are prone to leaking at the needle and seats.... a juiced up 65U is notorious for it.

  4. #4
    cheatin' piston popper addicted's Avatar
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    like salty said, it all depends on the motor. 2 cylinders don't shake as much as a triple and can usually run lower popoff. most triples need it high. Do realize though that the popoff pressure is not the actual pressure that the fuel pump needs to put out to feed the carbs. its just a way of measuring it.

  5. #5
    cyrillefrenchy's Avatar
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    sorry guys, it is a suv 1200 65u so should I lower the pop off round 55 psi?
    I am rebuilding the engine with 3 new pistons 1mm over due to huge water leak by the midshaft housing, saltwater has corroded the 2 rear crank seals, everything will be all new.
    thanks

  6. #6
    cheatin' piston popper addicted's Avatar
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    I forget the specs for the 65u but 55 is definately in the right ballpark. Much lower and it loads up real bad at idle because the needles are being forced to leak from the vibration.

  7. #7
    Look up a thread started by birdgod. Osidebill posted his "recipe for success" there for the mikuni 44 triples (search that term). He was quite the carb guru.

    While u are in there, double the tiny clear tongue shaped check valve as per his recipe. Stops the dribble in the carb throats nicely.

    55psi is his recommendation.

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  9. #9
    cyrillefrenchy's Avatar
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    very helpful, thanks
    I never drove the ski as I bought it with water damaged crankshaft due to mid shaft housing leak and water damaging rear crank seals.
    waiting for crank and bored cylinders to come in

  10. #10
    Yamaha artisan Cutlass's Avatar
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    55 psi with aftermarket flame arrestor. Use the stock 60-70psi (can't remember the exact number) with a stock airbox.

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