dean.psiropoulos(at)veriz
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 Posted: Tue Sep 15, 2009 9:11 pm Post subject: RV-List Digest: 20 Msgs - 09/14/09 |
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Interesting you should mention this Walt:
I have a similar problem with my RV-6A. A little history, the airplane was
signed off about a year ago and the first flight was right after
Thanksgiving. It ended with a dead engine during landing when over the
runway. Richening the mixture made it only slightly better so I began a 5
month quest to figure out why the engine didn't want to idle. I had some
feedback from people who said my problem was that I chose to use a wood prop
on an 0-360 engine WITH fuel injection. I was a bit skeptical and also had
feedback about checking for an intake leak so I went searching for a
possible problem there. I did find an intake leak, the hose clamp on the
number 1 cylinder intake tube at the sump. I tightened the hose clamp there
and also the intake tube bolts at the cylinder head (they weren't leaking
but were not at the correct torque). That helped only a little and didn't
cure the problem of the engine not wanting to idle when hot.
So I took up the advice of the "get a metal prop" crowd and bought a FP
Sensenich. It added lots of inertia (40 pounds vs wood at 15 pounds), which
would keep the engine turning over long enough to grab some throttle when it
wanted to quit but, it was a $2100.00 experiment that did NOT fix the
problem. So, I did what I should have done in the first place and checked
EVERYTHING in the fuel and ignition systems for problems. To make a long
story short, I discovered a sticky flow divider in the fuel injection
system. I talked to Don Rivera at Airflow Performance (mfgr of my injection
system) and he had me return the flow divider for repair. Once repaired, I
was able to lean the mixture to the proper fuel flow at idle and the engine
ran great, no stumbling or wanting to quit at idle with the metal prop. Don
did warn me that these systems will NOT always idle like a car and, that
engine stumbling would probably occur occasionally, especially when taxiing
after landing on a hot day.
After the flow divider was fixed I was always curious if the wood prop would
work now that the engine ran properly but didn't have the energy to do the
swap. Then, when Sensenich sent me a service letter requesting I return the
metal prop for radiographic inspection, I reinstalled the wood prop and have
been flying with it for a while. I also am experiencing a bit of a stumble
when taxiing back to the hangar after I land very similar to what you are
describing. I attribute it to what Don told me when he repaired my flow
divider. These FI systems are continuous flow types operated by atmospheric
pressure with no fuel returned to the tank during operation. The flow
divider and capillary tubes get hot because the engine is hot after you land
and the slow speed means cool air is NOT flowing over these parts (and the
fuel flow rate through the system is much lower). All that heat goes into
those stainless lines and the flow divider which, causes the occasional
bubble in the fuel which, results in the engine stumble you are
experiencing.
When I hear the engine stumbling I give a bit of throttle, what I don't like
is that I sometimes forget to retard the throttle and end up dragging the
brakes. Since I have the metal prop back in my possession now I'll
re-install it next time I have the cowling off but, for now, I like the
light weight and smoothness of the wood prop so I've been very happy flying
with it.
How long have you had this problem? If it wasn't a problem before and only
started giving you trouble recently (after several tens or hundreds of hours
of trouble free flying) then I'd say the intake leak is the most likely
suspect. If you just installed the prop and it has been giving you problems
from day one, then it may very well be what I describe above and you'll just
have to live with it. It's been an interesting education for me and I'm
just happy to be able to pass on my experiences now that everything is
working on my airplane. Let me know what you find out.
Dean Psiropoulos
RV-6A N197DM
Finally finishing Phase I
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