CCKB Engine Problem

[JBute 0]

Hello everyone: I am hoping that someone out there can help me solve a problem with an Onan CCKB engine that was brought to my shop today. I have not done anything with it yet. Problem is engine starts and runs nicely. It will rev to top rpms until it is fully warmed up. When warm it developes a dead miss on the left hand cylinder. Still runs okay on right side. If you slow it down below half speed the miss goes away. Also if you shut it off and restart it the miss is usually gone. Only happens when warmed up and operating at high speed. The owner has changed plug and left side plug wire before bringing it to me. He tells me the left side has spark to the plug even when missing. What would be the most logical place to start? When the plug is removed from left side after miss developes it is not oil fouled, but is wet with gas.I am thinking some type of valve probem perhaps. Has anyone ever had a twin cylinder engine do this? What did you do to fix it? Any help would be appreciated!! Thanks Much!!! Jim Bute

[MPH 12]

First I suspect the coil peters out when it gets hot. If not, might have a valve to too little clearance on the tappet, thus not closing good once warmed up good.

[Guest]

Remove the point box cover and observe while running the engine at RPM's that normally produces the miss.

[UCD 14]

Check intake runner and intake gasket on that cylinder.

[Marty-MN 0]

a new point box, plunger and points took care of a similar problem on one of mine. difference is mine would sometimes miss on left and another time the right or might run good.