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

From: Sky2high@aol.com

To: lml@lancaironline.net

Sent: Thursday, April 23, 2009 19:40

Subject: [LML] Re: rough IO-320

Terrence ands Gary,

 

Arrrrrgh!  I forgot Klaus' warning about the need to carefully redo the idle mixture settings (especially if a switch was made from mags to the EI).  I was surprised how much leaner the idle setting had to be.  We must remember that at very low power settings (idle), the timing might be 34 or more DBTDC.  F/A ratios are very important in this regime.

 

Grayhawk

 

In a message dated 4/22/2009 8:27:28 A.M. Central Daylight Time, casey.gary@yahoo.com writes:

Terrance,

I agree with Grayhawk's suggestions.  Yes, the Plasma III is a "double-strike" ignition and helps some for starting and idling.  A CD ignition such as yours can help with firing fouled plugs, but the arc duration is so short (a few microseconds compared to a standard ignition's few milliseconds) that if conditions are not good there could still be a problem.  Sounds to me like the main problem is simple plug fouling caused by a new engine being run on the ground for extended periods.  I had the same problem and had to clean the plugs multiple times in the first couple of hours.  In fact, for the first flight I cleaned the plugs and then waited till the path to the runway was clear of traffic.  Cleaning the plugs when they are just wet with oil - they can be washed with gasoline and then blown off with compressed air, or use a propane torch to heat the insulator until it gets dry and white.  It took about 50 hours before I could taxi without concern of fouling.  I agree with your desire to have it "run perfectly" before first flight, but it's impossible to do a break-in on the ground, so it will keep burning oil.  One telltale of "leaky" rings is the compression test - if it is almost perfect (80/80) it is likely that there is so much oil getting past the rings the oil will seal during the compression test.  A good sign of a "broken-in" engine is compression readings of about 76.

Another thought - after the potential air leaks are corrected - is that the RSA system is generally calibrated well for higher power, but the idle adjustment can vary.  After the plugs are clean and it will idle, check the idle mixture - it should be richened just enough to get an rpm drop of maybe 50 rpm from max.  It might be that the idle mixture is off enough to make it rough at low rpm.

Gary Casey

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Almost ready to aviate, but taxiing with engine that has been getting increasingly rougher, even after overhauling the Bendix RSA and testing the Plasma II CDI ignitions okay.  En ine sat for years, labelled preserved, but for about 5 years not run  after complete rebuild by Performance Airmotive about 8 or 9 years ago. 

Now, taxied and othrwise run-up for less than  3 hours, is becoming increasingly less inclined to idle.,

Initially would idle smoothly down to about 650-700rpm...

Then the lower plugs fouled/carbon and oil...replaced with new plugs at 2 hrs.;

then in another hour of ground running, runs strongly at 1500-2500 rpm, and when below 1500 mostly aggressively lean, still the bottom plugs again fouled in less than an hour, and minimum idle speed increased to about 900 rpm, running so rich it fouled plugs even with agressive leaning... suspected fuel injection servo had dried and cracked diaphrams, having sat dry for many years, so had it overhauled (Kelly)...

Ran it two days ago, and the minimum idle speed without competely cutting out, was 1000 rpm. Runs strong at higher rpms.

Will run a compression test tomorrow..

I want this mill to run perfectly before I fly it.

Any comments or suggestion welcome.

Terrence

L235/320

N211AL KGRE

 

 

-----Inline Message Follows-----

Terrence,

 

Test the induction system for leaks.  The rubber hose type seals where the air distribution system leaves the sump are the most likely candidates, although the gaskets at each cylinder can break down also.

 

Make sure that the adapter and plug anti-seize is appropriate. Stuff such as the Permatex silver colored goop can foul plugs to the point of misfiring.  Use something like the Champion black antiseize.

 

I believe the difference between the Plasma II and III ignitions is that the III system extends the duration of the spark and that can help less than perfect ignition conditions.  Perhaps you should re-check the timing with a light.  Do you have the optional display that allows you to check MAP, RPM and timing?  Loose timing data wires (can cause misfiring) or bad RPM and MAP data to the Plasma controllers could result in erratic ignition.  Do you have the crank sensors or the mag drive sensors?  The connectors to the mag drive sensors are, uh, not, uh, perfect.

 

While the ignition can be a bit off and still result in apparent OK operation, the F/A ratio is most critical with induction system leaks being most evident by poor operation at low power. Misfiring leads to plug fouling.

 

Scott Krueger AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)

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