Hey all hoping someone has seen this issue. Here is my series of events. 

  • 3300 engine runs perfectly smoothly 
  • upon annual inspection I find the scat tube going from air filter to carburetor has failed at the very spot the carb and scat tube meet, meaning I had been drawing raw air into the carb.
  • I replace the scat tube and I get a very rough running engine at high rpm, a known problem published by Jabiru where the scat tube creates disturbed air just before entering the carb. 
  • I replace the scat tube with the crosshairs air intake tube sold by Arion Aircraft which smooths out the airflow just before entering the carb.
  • now I have engine max rpm issues where i have these issues,
    • I can’t reach max RPM, even when I push throttle to the wall, I hit about 2800. 
    • even at 2800 I have engine roughness and not the smooth high rpm the Jabiru is capable of, though it smooths out at lesser RPM around 2300-2500. 
    • i am missing some power, I can’t cruise at my normal speed, it’s not climbing or cruising like it did.
  • In other news, my EGT has taken a nosedive, down to 300-400. Yes this could be related. It could be a bad gauge which do go bad often. Any correlation?

Questions

  • Is my air filter dirty? I’ll check soon but the massive drop in performance makes this seem odd given the FWF kit was done about 30 hours ago.
  • Do I need different carb jets/needles now that I have a different air intake journey? 
  • is there another issue like jammed spark plugs (which were fine at annual) or some other issue that I’m not thinking of?

any thoughts are appreciated, it’s driving me crazy. 

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To wrap up this thread, I ordered 2 new jets from Bing and have experimented with these. I had a 250, I went to a 245, and this raised by EGT's to their proper level and I am again at full RPM with additional power at the top end.

Yes I understand I only know EGT's for my front two cylinders (a problem Im working on) but at least now my EGTs' are indicating that Im burning at the temp Jabiru specs. 

Additionally, the belly of the plane is cleaner, indicating a cleaner burn from the cylinder. 

I am getting more power for less fuel burn. Life is good. 

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