Fuel Pump Clue requested

Thanks Denny, Having built the machine from plans, I do speak
hombuilt.
And I agree with your list of potential problems.
However, I will send you a beer if you can point me to a vendor who
will sell me a new diaphram for the pump. I sure have not been able to
find one. Do you think there might be an automotive diaphragm that
would work?
At this point, my money is on the inlet check valve leaking.
Sometimes. At shut down, the pump seems to hold pressure between
itself and the carb.
I hate to replace the pump not knowing that it is the problem, but I
am running out of ideas.

Thanks
Tim.


On 18 Dec 2006 08:33:20 -0800, "Denny" wrote:

Not necessarily... The leak can be contained and yet the pressure will
be down...
There are other possibilities: worn eccentric on the cam, worn plunger
rod, bad spring on the regulator, etc... But if it had been fine and
suddenly the pressure turned up low it is likely something sudden such
as a cracked diaphragm...
Parts can be had from a number of repair shops and or vendors.. Look in
Trade-A-Plane... Check on Sacramento Air Ranch, as one source of
parts...
The first thing is to pull the pump and have someone who speaks
homebuilt aircraft help you inspect it... Usually something will be
apparent...

denny

Tim Hickey wrote:
Thanks, Don, Good advice. I will


Zenith CH-300 Driver.

In article ,
(Tim Hickey) wrote:

Thanks Denny, Having built the machine from plans, I do speak
hombuilt.
And I agree with your list of potential problems.
However, I will send you a beer if you can point me to a vendor who
will sell me a new diaphram for the pump. I sure have not been able to
find one. Do you think there might be an automotive diaphragm that
would work?
At this point, my money is on the inlet check valve leaking.
Sometimes. At shut down, the pump seems to hold pressure between
itself and the carb.
I hate to replace the pump not knowing that it is the problem, but I
am running out of ideas.

Thanks
Tim.

Bad news. IIRC, diaphragm-type fuel pumps are NOT rebuildable!
Apparently, FAA thinks that there is too much opportunity for failure in
rebuilt pumps of this type. Also, automotive diaphragms are thinner than
those in aircraft pumps.

If your check valve is leaking, you just MIGHT be able to substitute a
new automotive valve.



On 18 Dec 2006 08:33:20 -0800, "Denny" wrote:

Not necessarily... The leak can be contained and yet the pressure will
be down...
There are other possibilities: worn eccentric on the cam, worn plunger
rod, bad spring on the regulator, etc... But if it had been fine and
suddenly the pressure turned up low it is likely something sudden such
as a cracked diaphragm...
Parts can be had from a number of repair shops and or vendors.. Look in
Trade-A-Plane... Check on Sacramento Air Ranch, as one source of
parts...
The first thing is to pull the pump and have someone who speaks
homebuilt aircraft help you inspect it... Usually something will be
apparent...

denny

Tim Hickey wrote:
Thanks, Don, Good advice. I will


Zenith CH-300 Driver.

A leaking diaphragm will often allow fuel into the crankcase and
the oil level will rise, smell like fuel and get really thin.
More likely it's a faulty check valve, or if the engine is one
that's flown for short flights, the spring in the pump has corroded and
broken, reducing the output pressure. The spring is on the crankcase
side of the diaphragm and the corrosive moisture and blowby gases can
attack it. If this is the case, the magnetos should be looked at as
well. Their impulse couplngs can corrode and their springs might break,
retarding the timing to around zero BTDC and lowering power to some
useless level. A real danger with the Bendix dual magneto used on some
Lycs. Both mags are driven by the one gear and coupling.

Dan