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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?
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