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I'm pretty well versed in the operation of this system. Pretty simple. Nevertheless, I have run into an issue that has me perplexed. Hoping for some insight. I have replaced 3 prime start diaphragms within an 1 1/2 hours of operation. I've never seen this before. Once the diaphragm fails I get the typical flooding at idle, fuel in the water, rough idle symptoms. Replace the torn diaphragm and bingo, runs like a top again.....for about 30 minutes. Then symptoms return. Pull prime start cover and shewalla, failed diaphragm. I'm tired of buying $15 dollar diaphragms for 30 minutes runtime. Let me hear your thoughts. Thanks from the Southeast.
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Also, the electrics of the system have been verified. 12vdc applied to thermo and it reacted 1/4" over a 20 sec period. -
can you tell or show us how the diaphragm is failing?
pin hole, large hole,or maybe a rip?
I would think the pulse port might exert too much pressure if there is a lean sneeze, but cannot think of anything else that would damage if installed properlyComment
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Thanks 99yam40 for your reply. All the tares are the same. Moon shaped on the upper starboard side of the pump. Approximately 1" long. I will post a pic when I pull the last failed 1 out. But all fail the same as described above. Side note: this motor is now a premix. Oil injection deleted.Comment
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when I said lean sneeze, I was talking about too lean on fuel to air not oil.
I am not really sure which crankcase that diaphragm gets it's pulse from, or if it comes from the crankcase even.
but I do know the regular fuel pump on those 3 cylinder motors get it's pulse from #3 cylinder crank case.
if there is a lean condition to cause #3 to burn fuel in the crankcase it will damage the diaphragm.
Are you hearing a hiccup or something strange while running the motor?
are you sure you have all of the tubing hooked up correctlyComment
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I'm not as familiar with the Primestart as 99yam40, but is there a spring or something that is or should be behind the diaphragm that would limit the deflection of the diaphragm?.....maybe the lean sneeze caused excessive pressure as mentioned....but my 1999 C90 Yamaha still has it's original Primestart and I'm confident I've had at least a few lean sneezes in 20 years, so your problem seems to be a mystery to me....keep us posted with what you figure out and good luck!Comment
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No lean sneeze while running. I do get 1 occassionally while starting ,but nothing major. I've built many johnson and evinrude 2 stroke motors. Mostly restorations. But this thing has me confused. I am going to pull the carbs and possibly the reed valves for a visual inspection.Comment
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