Engine backfiring through the exhaust

[Jeff J]

I have an O-200 with a couple of hours and 3 years since overhaul popping through the exhaust on both sides during a mag check on either mag. It would clear up if I brought the power up and leaned it out but the last time I flew it it starting popping with a power loss during climb out. The spark plugs in 3 & 4 are surprisingly clean while 1 & 2 are black. Number 4 has a bad exhaust valve leak. I removed it and spent nearly an hour lapping the valve but it still leaks as bad as before. The other 3 cylinders test in the high seventies. The valves all move with prop rotation. Intake parts all look good.

I am sending the cylinder with the bad valve to the shop. I have flown behind a lot of leaky exhaust valves and never had one pop like that in flight so I think there may still be a problem with the other side and the uneven fuel burn has me concerned.

Any ideas?

 

[lycominglou]

 

[Jeff J]

 

[Jeff J]

 

[bob turner]

 

[reileyr]

 

[JimC]

 

[Jeff J]

 

[Jeff J]

 

[Jeff J]