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Rear Cylinder Miss Fire! (SOLVED)

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Rear Cylinder Miss Fire! (SOLVED)

PostAuthor: Quarterbiker » Wed Jan 01, 2020 11:25 am

After much trouble shooting and following symptoms from normal procedures of diagnosis i finally found the problem. A small leak in the fuel pump was allowing fuel to pool in the vacuum line that runs to the intake manifold this was causing a rich condition and miss fire at idle and low RPM. higher engine speeds the bike ran fine. This was a slow developing problem, i first noticed the bike was getting slower to start and the mileage was dropping then the last couple of days it became hard to start and noticeable the rear cylinder was not running so it was time to find the problem

I call this engine a Happy Motor because it normally jumps right to life!

These symptoms could also be a week coil, fouled or worn out plug, carb problem, ECU problem. tight or sticking valve, low compression, cracked manifold and a few other things. I checked all of those before finding the problem. This vacuum controlled fuel pump is a first for me and others that i asked, it never crossed my mind this could cause Only the rear cylinder to miss fire! It has 1 carb and a shared manifold! Anyway for those that experience this problem and cant find the answer it might very well be the fuel pump.

I purchased a 22 dollar one from Amazon.

During this head scratching experience i discovered my valves were a bit tight, so check them every 5k miles or so. Hope this helps!

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Re: Rear Cylinder Miss Fire!

PostAuthor: mark75 » Wed Jan 01, 2020 5:00 pm

Glad you found the issue. Thanks for sharing.

I am going to mark as "SOLVED" to help others searching.
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