Today's Message Index:
----------------------
1. 01:51 PM - Re: Hard Starting CJ (Harv)
2. 02:56 PM - Fuel oddity and the little check valve no one touches. (threein60)
3. 09:51 PM - Re: Fuel oddity and the little check valve no one touches. (Walter Lannon)
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| Subject: | Re: Hard Starting CJ |
Glad you sorted it out.
For ref could you post a pic of where the primer nozzle is located, this is something
I'd like to check as I'm sure other will also.
Cheers :D
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=467513#467513
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| Subject: | Fuel oddity and the little check valve no one touches. |
Just wanted to give everyone a heads up as to an issue that I found on my CJ while
doing the annual. After my annual was complete, I rolled the aircraft outside
to do a run and leak check. I realize this was the wrong time to do this
since snow was moving in, but I wanted it to be complete. I had the cowls off
and with the cold temps, I needed to pay special attention to get the temps
up before I performed my checks. After about 10 minutes at warm up RPMs, I ran
to 85% for a few minutes than shut down to check for leaks. No leaks noted!
So I wanted to perform a second run and continue my systems checks for the final
inspection. I performed the same engine warm up procedure as before and
when the temps were sufficient I added power. The engine accelerated to 50% and
died! Let me tell you, the engine dying on the ground is somehow just as alarming
as if I were in the air. I performed a restart again. My start procedure
is to pressure with my electrical pump and then prim with the electrical primer
first. I found out each time I hit the start button with the electric
pump on, the engine would start immediately but when I turned the electrical fuel
pump off, the engine out die a few seconds late. I also noted that I could
not accelerate past 50% with the electrical pump on. This is odd because it
is designed to supply more fuel while on the electric pump than the engine can
consume on takeoff. Sent the mechanical fuel pump to M14P for overhaul (They
do a great job) and no real issues found. The odd part was with the fuel strainer
opened, I could not get any fuel to flow when I blew air into the wing
vents.
Long story short, the fuel check valve under the floor that supplies fuel to the
wobble pump, or in this case an electric pump was somehow failing closed. When
I removed it, it looked fine but randomly I could force it to fail open and
closed by shaking it. I removed the flapper and filed away any edges on the
hinge line as well as lapped the valve flapper surface. I also, noticed that
the brass hinge pin had VERY slight bend in it. I replaced this brass hinge
pin with a new, slightly larger diameter brass pin and reassembled. This seems
to have fixed the problem. Just wanted to pass this oddity along if you ever
have a similar issue.
[Shocked]
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=467514#467514
Message 3
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| Subject: | Re: Fuel oddity and the little check valve no one touches. |
I agree that really is an oddity!
However I don't believe it has anything to do with the fuel inlet check
valve. That valve does not supply fuel to the auxiliary pump (wobble or
otherwise). The fuel comes directly from the header tank via the 90 deg.
fitting on the input side of the check valve.
The valve is a simple flapper type identical to the two in the header tank.
It opens or closes in direct response to fuel flow. It almost literally
cannot fail if the hinge
is correctly positioned at the top (critical), the hinge pin is not too
tight (or falls out) and the flapper is not glued closed from storage with
serious fuel contamination. Held in your hand the flapper must fall freely
in either direction.
The only purpose of the valve is to close under aux. pump pressure and
direct fuel to the carburettor rather than back to the aux. pump. In normal
operation it opens instantly on sensing the negative pressure differential
from engine fuel pump operation.
I wish I could give you some idea what the real problem is but at this point
I really don't know.
Am I correct in assuming this is an M14P conversion and you have a non
standard vent system? Do you know the output pressure and volume (GPH) of
your aux. fuel pump?
The pressure ideally should be the same or slightly less than your engine
driven pump (usually 0.3 - 0.4 Kg/ sq. cm. or 4-6 psi ). Excessive over
pressure or GPH could
cause some problems but does not seem to fit your description.
Walt
From: threein60
Sent: Wednesday, March 22, 2017 2:53 PM
Subject: Yak-List: Fuel oddity and the little check valve no one touches.
Just wanted to give everyone a heads up as to an issue that I found on my CJ
while doing the annual. After my annual was complete, I rolled the aircraft
outside to do a run and leak check. I realize this was the wrong time to do
this since snow was moving in, but I wanted it to be complete. I had the
cowls off and with the cold temps, I needed to pay special attention to get
the temps up before I performed my checks. After about 10 minutes at warm
up RPMs, I ran to 85% for a few minutes than shut down to check for leaks.
No leaks noted! So I wanted to perform a second run and continue my systems
checks for the final inspection. I performed the same engine warm up
procedure as before and when the temps were sufficient I added power. The
engine accelerated to 50% and died! Let me tell you, the engine dying on
the ground is somehow just as alarming as if I were in the air. I performed
a restart again. My start procedure is to pressure with my electrical pump
and then !
prim with the electrical primer first. I found out each time I hit the
start button with the electric pump on, the engine would start immediately
but when I turned the electrical fuel pump off, the engine out die a few
seconds late. I also noted that I could not accelerate past 50% with the
electrical pump on. This is odd because it is designed to supply more fuel
while on the electric pump than the engine can consume on takeoff. Sent the
mechanical fuel pump to M14P for overhaul (They do a great job) and no real
issues found. The odd part was with the fuel strainer opened, I could not
get any fuel to flow when I blew air into the wing vents.
Long story short, the fuel check valve under the floor that supplies fuel to
the wobble pump, or in this case an electric pump was somehow failing
closed. When I removed it, it looked fine but randomly I could force it to
fail open and closed by shaking it. I removed the flapper and filed away
any edges on the hinge line as well as lapped the valve flapper surface. I
also, noticed that the brass hinge pin had VERY slight bend in it. I
replaced this brass hinge pin with a new, slightly larger diameter brass pin
and reassembled. This seems to have fixed the problem. Just wanted to
pass this oddity along if you ever have a similar issue.
[Shocked]
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=467514#467514
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