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ed - I like this concept, that the flow
is adequate for 1700rpm but not 2200, and that the initial 2200 rpm lasts until
the excess bowl fuel is gone. I did notice that I when I bypassed the
mechanical pump and ran strictly off the facet that I could shut off the pump
and nothing changed for a while even though the fuel pressure was zero.(when
running at 900 rpm). I think it is time to check filters and pickup tubes,
which makes more sense to me than putting the second mag back on!
you know, I've joked
about never, ever in 7 years, 850 hrs., finding any water in my fuel, since I
keep the plane inside. what a killer if all I needed was a damn fuel
filter!
my fuel pressure is
measured right before it enters the carb. my fuel system is tank(l/r),
filter(l/r), fuel selector switch, fuel flow meter, facet electric aux pump,
mechanical pump, fuel pressure regulator, fuel pressure meter, carb.(w/screen
filter)(mp4spa).
in theory then, if I
ran the engine at say, 1700, it should never cut out, or if at 2000 it should
take longer to reach the starvation point. heck of a time to be breaking
in new rings, no?
----- Original Message -----
Sent: Saturday, July 23, 2005 4:55
PM
Subject: [FlyRotary] Re: Lycoming
debugging test - -HELP!
Know next to nothing about Lycomings,
Kevin.
But, here are a few thoughts, you mention that you can
get the drop on the ground if you run it a minute of so at full power or in
the air around 300'. Two thoughts come to mind -
1. Fuel flow problem
2. Temperature induced problem
3. 2 possibly causing 1.
If you have adequate fuel to go with the air flow then
power/rpm should be maintained. So if the ignition is not the problem it
would seem it would have to be fuel flow. Where do you measure you fuel
pressure? If you are reading more fuel pressure now than previous, that
could imply fuel flow is less and therefore pressure is higher (before the
restriction). But, since it seems to act the same whether on 2 psi or
higher (although your message only mentions 2 psi) perhaps pressure is not the
key. Are your pumps in parallel or series? Could there be a leak
through or around one of the pumps. Have you tried it with both pumps
on?
It sounds like to me that you are getting adequate fuel
flow to support 2000 rpm for a limited amount of time and then for some reason
the fuel flow decreases. Since you have changed the carb, I would tend
to look at the fuel pumps or for a crimp/restriction in the fuel line
someplace. For instance, if you had a fuel filter that was partially
plugged up at lower rpm (requiring less fuel flow), there might be sufficient
flow to support 1700 rpm continuously. However, at Higher power
settings, the fuel being drawn out of the carb bowl may not be replaced (by
your fuel line) at a rate sufficient to support 2000 rpm. So once your
fuel out of your carb bowl is drawn down to the sustainable lower fuel flow
(1700 rpm), the power drops off and fuel requirement drops off to that
supportable Level. Sure sounds like a fuel problem to me, but then again
I know nothing about Lycomings.
Good Luck
Ed A
----- Original Message -----
Sent: Saturday, July 23, 2005 4:33
PM
Subject: [FlyRotary] Lycoming debugging
test - -HELP!
I realize that this isn't exactly the
right forum, but you guys seem to have excellent debugging skills. my
local RV group is totally worthless ("I find the carnauba wax doesn't show
fingerprints as much as the....")(except Mike!) the on-field mechanics
are sick of me coming by.
my O-320 RV-6A is
having RAG (rpm attention getter) problems. it runs fine until about
300' on take-off, then the rpm's drop to like 1700 (from 2200).
switching mags to electronic ignition(Rose) makes no difference.
mixture no diff. pulling the throttle it will seem to run fine at
1700rpm. I have 4 new cyls that I am attempting to break in.
ground run ups can only go like 2 minutes before CHT's exceed 400
degrees. I discovered I can get the rpm drop on the ground if I run it
a minute or so full power. cht's will typically approach 415 degrees
when the drop takes place. I don't know if the temp is significant or
not, it does seem that way. I have a brand new slick left mag.
rose checked the electronic ignition and could find nothing wrong, even put
it in an oven to test. I installed a new carb since the old one showed
signs of leakage (and I'm at whits end). no change. my fuel
pressure has been showing 8psi this last year, up from 6 psi when originally
installed.(no idea why) I installed a pressure regulator in-line which
works like a charm. I can dial whatever pressure I like. 2 psi
makes no difference. I bypassed the mechanical fuel pump and ran it
just on the facet electric. 2 psi, no difference. I discovered
that you can run the carb for maybe 30 secs with no fuel pressure while it
burns off the bowl gas. premier engines suggested induction leak making the
engine run lean. no leaks detected cold or hot engine. (pressurized
intake with vacuum, sprayed soapy water)
if the engine
didn't run right to start with then many explanations would hold. but
it runs fine for several minutes. it runs the same under mag or
electronic ignition both before and after the problem kicks in.
everyone really wants to blame the rose ignition, but I'm not seeing any
connection. with such a quick run-up my oil temp barely registers, so
I doubt parts are seizing. I have new mineral oil in it for breakin
right now. there is a bit of MMO in the fuel too I believe, left over
from a mechanics "what the hell" attempt from way back. my cyls are
all new, rebuilts, so no valve problems. I checked the push rod
lengths when I reinstalled them. the engine isn't missing when
the problems occurs, it simply won't run faster and it seems to prefer the
throttle pulled back to match the rpm it is putting out. I can't
figure out any more lean mixture scenarios to try. the new carb runs
just like the old one did. I recently replaced the mag harness with a
much newer, used one. I tested it and it was fine. the plugs are
all new, but again, no diff between mag and elec ignition. if I flip
the ignition to R and shut off the elect ig then the engine quits as would
be expected, no wiring problems.
fuel, spark, air,
timing, that's all there is. this damn lycoming lawn mower has me
stumped. my engine has been running fine up until this (hey, we all
have "cracked" cylinders, get out your microscope and look!). you guys
have any ideas?
----- Original
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