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A mechanic and I are out of ideas trying to solve a three week old problem on the 85HP (converted from 75HP) engine on my 1946 415C, N2738H. Any advice and help anyone can give us would be greatly appreciated. The problem surfaced at run up with a 200RPM drop on the right mag. This was after 25 hours (about 25 flights with no problems of any kind) Left mag was normal with about 25-50 RPM drop. The right mag had 25 hours on it, the wiring harness and all 8 plugs had 25 hours. So far we have done the following: 1. We bought a rebuilt right mag from Aircraft Spruce to replace the one with 25 hours. Installed the new mag with no change; still a 200, or more, RPM drop on the right mag. Even had minor backfiring. We bypassed both key and p-leads with no change, still a 200 RPM drop on the right mag. Then we reversed the mags with no change, still the 200 RPM drop on the right mag. We concluded at this point that it was not a mag problem. 2. We installed 8 new plugs to replace the plugs that had 25 hours on them. No change, still a 200RPM drop on right mag. 3. About this time we ran the engine on the right mag long enough to identify the cold cylinder, #4. 4. We installed a new wiring harness to replace the 25hour harness. No change, still the same, or worse, RPM drop on the right mag and #4 was still cold. 5. We then again loosened the front cowling and removed the metal cover from the #4 cylinder plug and directly wired the wire to the plug without using the plug cover. This engine still has the small plugs on top. No change, still the excessive RPM drop on the right mag. 6. At this point we think we have eliminated as the problem the mags, the plugs, the wiring harness, the covers on the top plugs., the P-leads and the key system. And the engine/mags have been timed several times with the left mag showing no problem and the right mag continuing to show the excessive RPM drop, so we think we have eliminated timing as the problem. We also think that a problem internal to cylinder #4 would affect both mags and not just the right one. We have run out of ideas and really need your help. Any ideas/possibilities would be greatly appreciated. Thanks, Dennis Hatfield N2738H. ============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm
