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1967 Evinrude 18hp Fastwin low speed sputtering and missing
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<blockquote data-quote="Boat2fast" data-source="post: 353941" data-attributes="member: 13358"><p>Sometimes you can unplug one plug wire to see if the opposite cylinder will run the engine. Both cylinders should do an equally good job of running by themselves. If the engine runs on the top cylinder but won't run on the bottom one, then you have narrowed the problem down.</p><p></p><p> Popping or sneezing is from a lean condition. A bad crank seal is most often the culprit. Air leaking into the crankcase at idle(high vacuum)disrupts the fuel air mix for that cylinder. This causes the lean pop or sneeze. You have noted that the problem goes away at medium and full throttle. </p><p></p><p> The leak(s) don't affect fuel air mix at higher speeds because there is no vacuum in the crankcase...high air flow through the engine. The leaks are tiny compared to the amount of air flowing at higher speeds. The leaks are larger in comparison to the small amount of air going through the engine at idle. </p><p> </p><p>Other air leaks can be from the fuel pump, crankcase parting line, transfer port gaskets, etc.</p><p></p><p>Another thing that can happen sometimes is the fuel pump will leak fuel into the cylinder it's running off of. That will gag that cylinder with too much fuel. If you can suck air/fuel from the vacuum port on the back of the pump, it's leaking fuel into the crankcase.</p></blockquote><p></p>
[QUOTE="Boat2fast, post: 353941, member: 13358"] Sometimes you can unplug one plug wire to see if the opposite cylinder will run the engine. Both cylinders should do an equally good job of running by themselves. If the engine runs on the top cylinder but won't run on the bottom one, then you have narrowed the problem down. Popping or sneezing is from a lean condition. A bad crank seal is most often the culprit. Air leaking into the crankcase at idle(high vacuum)disrupts the fuel air mix for that cylinder. This causes the lean pop or sneeze. You have noted that the problem goes away at medium and full throttle. The leak(s) don't affect fuel air mix at higher speeds because there is no vacuum in the crankcase...high air flow through the engine. The leaks are tiny compared to the amount of air flowing at higher speeds. The leaks are larger in comparison to the small amount of air going through the engine at idle. Other air leaks can be from the fuel pump, crankcase parting line, transfer port gaskets, etc. Another thing that can happen sometimes is the fuel pump will leak fuel into the cylinder it's running off of. That will gag that cylinder with too much fuel. If you can suck air/fuel from the vacuum port on the back of the pump, it's leaking fuel into the crankcase. [/QUOTE]
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1967 Evinrude 18hp Fastwin low speed sputtering and missing
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