Puff-Puff Sound from Keihin Carb (Honda CRF150F)

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  #1  
Old 12-02-14, 10:43 AM
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Puff-Puff Sound from Keihin Carb (Honda CRF150F)

The carb on my nephew's 2007 CRF150F makes a loud puff-puff sound in unison with the exhaust note. I took off the float bowl and cleaned the jets and most of the passages, but the sound is still present. Any clue what could be causing this abnormal sound? I should also mention that although the bike starts right up, the RPMs slowly die down and the engine cuts off. The only way to keep it idling is to turn the idle screw fully CW or hold the throttle open a bit. Air filter is clean, spark plug is good, jets are clean and fuel flow is good.
 
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  #2  
Old 12-02-14, 02:02 PM
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Do a compression test. It sounds like the intake valve is not sealing completely on the power and or exhaust stroke.

Slightly different subject, but if the bike is new to you or your nephew, do not use "energy conserving" oil. You have a wet clutch and that type of oil will cause slippage.
 
  #3  
Old 12-02-14, 06:03 PM
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He's had the bike for over a year and it was running just fine this past summer. It was only over Thanksgiving break that I realized it was running poorly. I cleaned the jets and put in some fresh gas and it started right up, but like I said, it won't idle on it's own and stumbles when cracking open the throttle, and the repetitive puff puff noise. When it was running, it would pop a lot on decel if that's any indication.
 
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