Lee. That might be that rich mixture fires out of the exhaust.
But this case here is totally clear. In a glide you are closing the throttle. But the prop windmills the engine. The engine now wants more fuel air mixture than it can get ( you closed the throttle) It creates a vacuum behind the throttle. If any yet so tiny air leak exists, now is the time to let air into the manifold. That extra air leans out the mixture to an extend that it does not fire in the combustion chamber but later when it comes into the exhaust where it is hot and bang bang you get some backfiring. ( A friend of mine blew up a muffler on his VW Beetle - I enriched the carburetor and all the firing was gone) The case is also clear because to replace the exhaust pipes one needs to take off one, if not both intake elbows. There is just not enough room to get in between with your wrenches. When putting it back on one can either forget to tighten completely, use the old gasket. Use a new gasket, but did not clean out the old gasket or use no gasket. Many possibilities are there. The lean condition on an engine cold start is due the fact that the cold engine has many places in the induction system where the fuel air mixture can condense, leaving the fuel on the intake walls rather than going into the cylinder. When one tries to overcome that with heavy priming and that maybe over and over, you'll most likely end up with a gasoline puddle in the engine compartment that is ready for ignition. That of course will ruin anyone's day. This is how I understand the whole thing. I might be wrong, I was wrong many times on this forum. Hartmut ----- Original Message ----- From: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] ; [email protected] Sent: Wednesday, October 24, 2007 12:16 PM Subject: Re: [ercoupe-tech] Backfiring on glide Hartmut, I believe that a rich fuel mixture causes backfiring in the exhaust. A lean mixture results in a backfire through the carburetor. Lean mixtures usually occur on a cold day and are the usual cause of an engine fire upon starting the engine. Something is causing the mixture to richen when the throttle is closed. Lee -- "Hartmut Beil" <[EMAIL PROTECTED]> wrote: John Backfiring happens when the mixture is too lean. If the exhaust stack has been replaced, the intake elbows might have been taken off as well. I would check for intake leaks at these elbows and for intake leaks in general. If the engine behaves otherwise normal that is. Any abnormality is one indicator more toward the problem. Hartmut ----- Original Message ----- From: John Roach To: [email protected] Sent: Wednesday, October 24, 2007 4:13 AM Subject: [ercoupe-tech] Backfiring on glide I recently replaced the exhaust stack on the pilot's side of the engine. Since that time, the engine seems to be backfiring when I close the throttle to land. I checked it today and the backfiring seems to start between 70 and 65 mph. The A&P has checked everything he can think of and has no idea what is causing the problem. I was flying with the canopy closed and wearing a headset today and even with my poor hearing it seemed disturbingly loud. Any opinions welcome. John Roach N 2427H _____________________________________________________________ Help others. Click here to begin a career in the healthcare industry.
