August 26th 04, 12:45 PM
In rec.aviation.homebuilt Richard Riley > wrote:
: The engine has about 60 hours since new. My friend was the pilot for
: the last 4 hours or so. As he's been flying it he's been getting much
: higher fuel burn than he expected - cruise lean was 18-20 GPH. He's
: also seen higher oil temps than expected - 220-240.
: The mags were unchanged from their original factory timing, but it
: turns out they were set at 18 and 20 degrees.
: Any ideas here? He was running it at no more than 25" and 2500 RPM.
: I'd have thought all that fuel would have kept it cool.
: Richard Riley
Was the fuel flow (i.e. pressure) gauge calibrated? If it was reading high
and adjusted for that, it would run too lean. Was he verifying fuel burn by the
amount put in the tanks after a flight? I concluded that my Cherokee was running 5%
harder than indicated via tach and MP by the fuel I put in the tanks after the flight.
I calibrated the tach with a strobe and found it reading 50 rpm low.
Also, mismatched mags off like that will increase combustion temps and
pressures. I don't know what the standard setting is for that engine, but it doesn't
sound like they were advanced too far.... if anything retarded too much. Could have
cooked the exhaust valve from being too retarded and caused preignition.
Lots of possible options.
-Cory
--
************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering Ph.D. Graduate Student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************
: The engine has about 60 hours since new. My friend was the pilot for
: the last 4 hours or so. As he's been flying it he's been getting much
: higher fuel burn than he expected - cruise lean was 18-20 GPH. He's
: also seen higher oil temps than expected - 220-240.
: The mags were unchanged from their original factory timing, but it
: turns out they were set at 18 and 20 degrees.
: Any ideas here? He was running it at no more than 25" and 2500 RPM.
: I'd have thought all that fuel would have kept it cool.
: Richard Riley
Was the fuel flow (i.e. pressure) gauge calibrated? If it was reading high
and adjusted for that, it would run too lean. Was he verifying fuel burn by the
amount put in the tanks after a flight? I concluded that my Cherokee was running 5%
harder than indicated via tach and MP by the fuel I put in the tanks after the flight.
I calibrated the tach with a strobe and found it reading 50 rpm low.
Also, mismatched mags off like that will increase combustion temps and
pressures. I don't know what the standard setting is for that engine, but it doesn't
sound like they were advanced too far.... if anything retarded too much. Could have
cooked the exhaust valve from being too retarded and caused preignition.
Lots of possible options.
-Cory
--
************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering Ph.D. Graduate Student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************