“On High Boost for about 10 seconds, I got about a
pint of fuel out the sniffle valve. Hmmmmm, it’s not supposed to do
that.”
Oh yes it is suppose to do that
if you have a newer Continental Engine. Continental changed the fuel pump
design a few years ago and if the engine is NOT running, the mixture is in full
cut off and the boost pump is on……this will NOT prevent fuel from
pouring out of the sniffle valve. This change made by Continental
prevents me from using my standard hot start procedure of letting the fuel circulate
for 30 seconds while the throttle is wide open, the mixture in cut off and the
high boost on. Now the fuel pours out on the ground……not good.
Craig Berland
IV-P
On climb out to 14,500’ yesterday I was having trouble
leaning to 1300 degrees. The mixture knob was extra sensitive so I
favored the rich side. I had just topped off with 40 gal. from an
above ground tank that was probably around 80 to 85 degrees. Low
boost was used from takeoff to about 1500’ agl., RPM was reduced to
2500 and leaning began. Normally, maintaining 1300 degrees on the
hottest cyl. in the climb (per The Advanced Pilot Course) is easy.
(On the previous flight to 15,500’ for 2.5 hours I noticed it did
not lean normally but I was able to go LOP and it held the fuel flow @ 9.8
gph. No fuel had been added and temp on the ground was about 70 degrees.)
When we reached 14,500’, we accelerated in level off, reduced
RPM to 2300 and started to ease the mixture knob back to go Lean of Peak.
At 16.5 gal. per hr., slowly turning the Vernier about 1/8” as normal,
fuel flow jumped to 9 gph. with the engine faltering. I tried this twice
before concluding “this ain’t right”. I wish I
had thought to use Low Boost or to check Fuel Pressure, but I
didn’t. We were over the Sierras and headed for the nearest airport
but maintained altitude and finally circled down over home base. I
did not mess with the mixture on decent thinking a running engine was the best
option.
The control cable, bracket, arm and movement on the mixture
are OK. Testing for leaks, I had the mixture in idle cut off, throttle
open full. With Low Boost for about 10 seconds, no leaks. On
High Boost for about 10 seconds, I got about a pint of fuel out the sniffle
valve. Hmmmmm, it’s not supposed to do that.
Sounds like the Metering Unit, what do you think?
Steve Colwell Legacy IO-550N mostly stock, no
ram air or injector mods., 225 hours tt.