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The O360-A4K on my ’79 Tiger was been running rough from 1000-1500 RPM especially in the morning. The mechanic and I reamed all four exhaust valve guides. This made it a little better but not back to normal. The mechanic said it was the carburetor so I got a re-manufactured HA6 from Western Skyways. Still not right. The magnetos are 50 hours in service since new and the wiring harness is about 100 hours since new.The mag drop is 75/75 at 1800 rpm. Carb heat check at 1800 RPM was -50RPM. On the ground the roughness is between 1000 and 1300 RPM. In the air, it is rough between 2000 and 2150. In the descent yesterday I heard one backfiring event after the throttle was retarded. The primer o-rings were replaced last week. Any ideas on what to do next would be greatly appreciated.
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Don’t know if this will help. I had a 71 Piper Comanche 260C. I had a similar problem that when I first started it it was rough then after flying it for about 1/2 – 1 hour it would be smooth. No one could give me an answer, not Lycoming or anyone in our group. After spending a lot of my time and money overhauling may parts it was the exhaust valves ( they had carbon build up ).After it got hot they expanded and ran smooth. You can have the exhaust valves removed and honked or overhaul the cylinders. I would have a shop borescope the cylinders and check. Cheaper to hone them. Hope this is some help. I now have a 79 Tiger really like it and a lot less to maintain.
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