Kevin, your plane is old enough that you could have sloshed the tanks.  Do your tanks have slosh sealant?  If so it could be coming off about now.  Mine has started to wrinkle and split in some places.  It's now time for me to pull my tanks, they were built in the mid 90's.

Mike
Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR
13B in gestation mode, RD-1C, EC-2


At 17:15 2005-07-23, you wrote:

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?
Kevin Lane  Portland, OR
e-mail-> n3773@comcast.net

----- Original Message -----

From: Ed Anderson

To: Rotary motors in aircraft

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 -----

From: kevin lane

To: Rotary motors in aircraft

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?

Kevin Lane  Portland, OR

e-mail-> n3773@comcast.net

----- Original