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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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