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Old 12-14-2011, 02:46 PM
sirlegin's Avatar
sirlegin sirlegin is offline
Join Date: Feb 2006
Location: Keller, Texas
Posts: 326
Default Rough engine at 1500-1700 rpms

This is an injected Lycoming OF-320. Catto 3 blade fixed pitch. 10 hours
The engine starts and idles nicely, however both on the ground and in the air when the throttle is advanced to 1500rpm the engine becomes rough and does not respond well to the throttle until 1800 rpms are reached and then the engine will play catch up and go to 2000 rpms.
While at 4500 ft and after about 35 minutes of flight I could get no rpm's above idle. I switched tanks from left to right with the boost pump on and after a little while, varying throttle settings, the rpm's came back. I had switched the tanks after 30 minutes from right to left about 5 minutes earlier. I think this was more coincidental rather than significant. When I did have rpm's I was also getting backfires. There was no holding a set rpm and surges of 1 to 300 rpm on any setting above 1200 rpm was the norm. There was alot of throttle movement with no reaction from the engine.
The engine never made full power and at best WOT at cruise was 2500 rpm.
I ran it up back at the hangar and the same dead zone at 1500 to 1700 rpm was evident but none of the other inflight symptoms.
I have changed the injectors, sealed induction leaks, cleaned fuel filters and have run out of idea's.
Below is a graph of the MAP vs engine rpm's and there is a definate lack at the dead zone area. 1500-1700 rpm's.
I have a K&N filter which was recently cleaned and re oiled, perhaps too much oil?
Any thoughts would be greatly appreciated.

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