Paul Whetstone wrote:
Sorry but I'm just getting a little time to follow these forums. Paul last had his annual done by us here at Texas Rotax and Light Sport Aircraft, LLC. We are an authorized Rotax IRC just north of San Antonio, Texas. I had written an article that is posted on our website, www.txlightsportaircraft.com under the service section that talks about this very problem and explains what we now do to the Rotax exhaust system on a regular basis. I sent that to Paul and he confirmed my logic and findings. He is not the only iS engine we have found that destroys mufflers. All cylinders rising in EGTs should be taken seriously. The aft cylinders may even be damaged. Hope the little article helps. A dongle would have helped diagnose this but he was way away from San Antonio. I applaud Paul for his persistence and this should be watched on a regular basis.
Thanks Paul, your article was right on the money. Unfortunately we had found the issue accidentally a couple of days prior to receiving it. Had we not spotted the small crack we would not have pulled the muffler and found the baffle pieces rattling around in it. A little earlier in the thread I asked how this could be inspected. Unfortunately that seems to be pretty difficult without pulling the muffler. And even then there is only so much that will be visible.
I did have a BUDS dongle and pulled the logs. These were sent to multiple experts to review, but nothing definitive was found. Everything that was common to the engine and not being managed by redundant sensors was checked (fuel system, air system, grounds). The low RPM problem showed no faults at all. We even had a loaner ECU sent in to check the system. Perhaps the signs in the logs were missed. It would be helpful to know that those would be.
I can add that the new muffler system used by Rotax is miles ahead of what was on my engine (2015 time frame). It is clearly built like a tank where the other seemed quite delicate. Anyone trying to weld the original gave no guarantees as the walls were so thin. If an old muffler is still working it would be hard to spend the money to replace it. But the new muffler may be worth the piece of mind.
Looking way back this issue seems to have started with the Kitfox original construction. The hole in the cowling was too small from the beginning. At startup the engine moves quite a bit and the exhaust pipe was bumping against the cowling hole. There were marks where this was happening on both sides of the exhaust pipe. Eventually the thin wall construction of the muffler just gave way. This caused a chain of issues as the muffler was welded for repair. In hindsight I should have simply replaced the muffler system. But when checking on a purchase I was told it would be a special order that would take months to get. And I was encouraged by many to simply get it welded.
Perhaps the moral of the story is if an engine won't make proper RPM's and everything else looks good with no faults, pull the muffler and check it.
