TIO540-J2B no rise in RPM during shutdown

[gsimmer]

I have a TIO540-J2B in my Navajo. Had both the fuel servos overhauled over the winter. Ever since, the right engine has never had a good rise in rpm when the mixture is pulled. We have adjusted the idle mixture a couple clicks at a time and when you think all is working correctly the engine just shuts down without the rise in rpm after a couple flights. We have adjusted the mixture so rich that when the emergency boost pump is turned on for takeoff, if the engine is at idle it will flood the engine. A couple other things I noticed is while at idle the engine analyzer shows that engine at 6 gph while the left is at 4gph. If I turn on the boost pump on the right engine the gph drops to 4gph to match the left engine.The engine doesn't change how it is running with the emergency pump on or off. Also if I leave the boost pump on during shutdown I do get the rise in rpm. This plane has the mechanical fuel pump, an electric pump that runs all the time and the emergency pump. Is it possible that I am sucking in air somewhere leaning out the fuel as well as causing the totalizer to read higher than it really is. I would think 6gph at idle would flood out the engine and it doesn't. Both engines run great just no rise in rpm on shutdown on the right engine. Any help in troubleshooting this would be great.

[Tim Glubaskas]

Sorry we have been off the board for a few weeks -
If you still would like some help with this drop me an email and we will setup a time to chat about it if you think that would help

t

[gsimmer]

So I replaced the mechanical fuel pump and I thought everything was good. We set up the idle mixture and got the rise in RPM as expected. Flown it for almost a year. The engine runs real good ROP but LOP there has always been a slight miss. Today running LOP the engine started missing bad. Can't say it was backfiring but it was missing bad enough to shake the airframe. Did a LOP mag check on both mags and you could here the engine popping and backfiring. Doing a mag check ROP everything was good. Now having said that if the issue here was ignition I would think a mag check LOP would show one or more cylinders failing the mag check. I do get a rise in EGT on all cylinders. Could this be fuel related instead of ignition related. Servo was overhauled a year and a half ago. It has been suggested from the overhaul shop that maybe air is being introduced into the fuel system before it enters the servo maybe through one of the electric pumps. How do you T/S that.

[klausnw]

It's common for a hot spot in the cylinder to cause backfiring and roughness on both mags. Sometimes a spark plug will have a little carbon deposit on it or the carbon in the cylinder becomes an igniter. An intake system leak, fuel injector blockage and cylinder cracks also cause backfiring.