High Fuel Flow

[Doug Kimball]

Recently purchased a 61 - PA 24-250 and my fuel burn is running about 2 gal per hour higher than the power setting says it should be.

It is an o-540 with 110 SMOH and the carb was overhauled at major. I have checked the Fuel Flow computer and calibration seems to be accurate when checked against the fuel used on refill. 6 Cyl engine monitor does not show any single cylinder running out of tolerance indicating an intake leak on a cylinder.

I have tried high power and low settings. High altitude cruise and low and fuel flow always runs substantially higher than book. I know book could be unrealistic on the numbers but my son had a Saratoga and it burned sustainably less fuel per hour than the Comanche with a larger fuel injected engine.

Any ideas on where to look next?

Thanks,
Doug

[md11flyer]

Doug, how are you leaning the engine during cruise? If you cruise at say 8000 feet, when you are using the
book, setting your manifold pressure for the power you want, say 65%, can you not lean the engine to the book fuel flow?
And if you can't is it 2 gallons per hour more than book at all power setting? What are your speeds are they book values for the
power settings? You might have an incorrect reading manifold gauge.

Gary

[Doug Kimball]

Speeds are close to book if not on the low side. If you lean to book fuel flow the engine is extremely rough. I have been leaning to rough and then rich just a little .

[Clarence Beintema]

Hi Doug,

It may be that your fuel flow is correct, it could be that your tachometer and manifold pressure gauge are incorrect and you are actually running more power than you think. Book speed may not be attained even at higher power due to a poorly rigged or draggy airplane.

Clarence

[Andrew Foster]

We have a 61 250 with an 0-540. We have a JPI FS 450 fuel flow and an EI engine monitor. At 75% power and leaned to 50 rich of peak from the first cylinder to peak we average about 16 GPH on the JPI. This nets about 175 - 180 MPH. The fuel flow varies as the float bowl fills the carb. I can ball bark the mixture with a flow somewhere around 16-15 GPH and that will net best power. This at an altitude between say 6-10 k . Above that I lean with the engine monitor and fuel flow will reduce to 14-12 GPH. We only lean below 75% power.
However. Once the total flight is done, the average fuel flow is about 14 GPH, most likely because of the reduced flow during descent and approach. This corosponds to the book value of an average of 14.2 GPH.

Any 250 drivers out there with Fuel Injection?
We were thinking about the conversion and wondering what fuel savings we might see.

Thanks
Andrew

[Doug Kimball]

I greatly appreciate the suggestions. I will be checking the Tach and MF gauges for accuracy.

Thanks Andrew, for your observations. I will check things closer on the next flight.

Does anyone have any thoughts about Carb jets? In speaking with the Lycoming Engineer at Oshkosh, he brought up the idea that incorrect jets could have been installed at overhaul.
Doug