Hi group,
Here is another problem to solve. I have noticed a roughness at the middle range
of RPM on the 914 engine. During run-up, I have never gotten better than about
300 RPM drop - usually more. Bottom line - a not very satisfying run-up. It
has always been that way. I once had a problem with very rough running after
pulling the engine back to cruise power. That turned out to be a split in one
of the little rubber hoses coming off the airbox - a simple fix. In the last few
hours of running, I am getting a similar roughness, but much more subtle. On
today's flight, a mag check at about 25 inches and 5000 rpm reveals roughness
on each mag - equally. If I keep the 25 inches and increase the RPM to 5500,
the mag check is smooth. IT is very smooth at climb power of 35 inches and 5500
RPM. Also, I have been getting an increased shaking at taxi speed with the
rpm at about 2500, when the engine is cold. That is a new thing too.
Upon returning from OSH, I noticed green stain that appeared to be coming from
my drain lines from the airbox/carb catch bowl. To experiment, I put a catch
container
in the airbox drain line. I always thought it was putting out oil there,
but this morning inspection it became obvious it is fuel, not oil. There is
fuel in my airbox.
The way I understand the system, there is a line from the airbox to the airbox
pressure sensor and the fuel pressure regulator. That is how it maintains the
fuel pressure at 2 to 5 PSI above airbox pressure. There are also two more
connections
to the airbox going from the right side and the left side to a valve
of some sort and then from there to the carb float bowls - presumably to keep
them pressurized. There is an electrical connection that goes from this valve
to the computer, so I think it uses a different pressure tap from the airbox to
pressurize the carb float bowl depending on the throttle position. There is
a throttle position sensor on the port carb.
What if the proper pressure is not getting to the carbs - where there is too
much
fuel pressure, therefore causing the carb float bowl to overflow? That is what
they say in the operator's manual. What other way could fuel be getting into
the airbox? Has anyone ever seen such a thing on their 914 engine?
I never get easy problems. They always seem to be perplexing problems and always
on Friday night or Saturday morning so I have to wait 48 hours before I can
start to deal with them.
Thanks,
Dave
A227
Mini U2
232TT
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