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Discussion Starter #1
I've been working on my CB350 for about the last couple of months. I had blown the left cylinder about a month ago and replaced the engine with a Craigslist find. The new motor was very clean. It came with carbs, coils and wiring. I installed the motor and did a full tuneup on it. Cam chain adjustment, valve clearances, ignition points/timing, cleaned the advancer, carbs cleaned and floats adjusted. I could never get the bike to run properly. I eventually identified an air leak at the left carb boot. I was certain that it would solve my high and erratic idle, and it did to a degree. But the bike still wouldn't idle very smoothly. The idles would rise dramatically 4 - 5K rpm as the engine warmed up.

Anyways, after rechecking my valve clearances and timing(which was a PITA with the idle being all over the place), I decided to buy a compression gauge and check the compression. I found that the left cylinder has about 128 psi and the right was about at spec at 170. I put a few drops of oil in the left cyl and checked it again. It came up to about 167. So I'm thinking that it's not the valves. I'm going to start pulling the motor this week. I've worked on my own bikes for the past 5 years, but have never had to crack open a motor. What should I be looking for?
 

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Sensei
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27,163 Posts
Stuck rings..... Time for new ones my friend......You won't know for sure what /or If anything else needs attention until you open her up....
 

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Discussion Starter #4
Thanks for the replies. I will be pulling the motor today.

Btw, here are some pics of the old motor for your viewing pleasure.




 

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That's a textbook pre-detonation hole, my friend.
Caused either by severely advanced timing, or (more likely) extended use of sleazy low-octane fuel......
 

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tbpmusic said:
or (more likely) extended use of sleazy low-octane fuel......
I am now mixing 1/4 gallon of 111 leaded race gas to a tank of 91 octane unleaded pump fuel in my CL350.
 
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