Different Fuel flows - Front and rear

[Nick Bailey]

My fuel flows on front and rear vary about 3.5 gals between engines at WOT , very noticeable on climbout. Front is much lower. I had not been paying much attention to fuel flows on climb, but noticed that when I ground leaned, I could barely touch front engine fuel knob before losing power. Rear engine could be leaned back almost an inch of travel before losing power. I note that chts on front are slightly higher on climb, perhaps due to lower fuel flow. Can my A and P adjust these? Is there a setting which Continental recommends?

[Ernie Martin]

It's OK for there to be some difference in fuel flow, but yours seems excessive, especially the huge difference in leaning capabilities between the engines. These fuel injection engines need to be calibrated using special guages and following the manufacturer's recommendations. For those in northern latitudes (not you and me), I've heard that the calibration ought to be done twice a year, for cold and hot weather. Although I believe an A&P can do it, provided he/she has the specified guages and the procedure, I take it to a specialist who does it often, to make sure it's done right.

Ernie

[KyleTownsend]

Nick:

It sounds like the front engine is probably running excessively lean at full power settings. From what I understand, it is very important that you are getting red-line fuel flows at these power settings to insure sufficient detonation margin. I'm no expert, but I am plenty paranoid about these expensive engines. I would be reluctant to fly it at full power until I got this looked at.

[Walter Atkinson]

NIck:

Do you remember the engine run where we showed you the high ICPs and thetaPP close to TDC when the engine was ROP and not rich enough? As soon as the fuel flow was turned up above the redline, the ICPs went down and the thetaPP moved further from TDC. That is the problem with your front engine. GET IT FIXED. It is very easy to address (one screw) and should be done to lower the heat and stress that engine is enduring.

As to the fact that in twins the FF is rarely the same, that is true... BUT, they both should be adequate, which your front one is not.

The biggest problem with a twin is that you have two engines to *compare* with one another!!! <g>

Many pilots and mechanics will say that this engine is operating too lean. We know what they mean, but that is technically inaccurate as it is still a rich mixture. It is not a lean mixture. It would be less confusing and more accurate to say that your front engine is not running rich enough. Yes, it's semanitics, but it's a rather significant conceptual difference.