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Carbon Cub Rough Running Engine

I have chronicled my data in this thread. Result of a customer leaning his Carbon Cub SS in cruise flight how he had done his old Cessna for years and ended up burning an intake valve. Bobby Loper at ECI was a good source on the ignition and leaning conclusion.
 
I have chronicled my data in this thread. Result of a customer leaning his Carbon Cub SS in cruise flight how he had done his old Cessna for years and ended up burning an intake valve. Bobby Loper at ECI was a good source on the ignition and leaning conclusion.

Ok, but was the typical cruise power setting for that customer's airplane less than 60%?
 
I don't know. At the time he had no sort of engine monitoring system. Oil temp and pressure were it. Adding CHT and EGT told him what he needed to know to lean the engine without burning it up. What rpm is 60% on an O-340?
 
So what is the best way to lean a engine with electronic ignition?

If you use the max rpm: 2700, the 60% is 1620 rpm.
 
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An electronic ignition will burn a lean mixture where a conventional magneto will start to stumble. The old way of leaning till it stumbles and enrichen a bit does not work on electronic ignition, you will burn something.

Interestingly, and perhaps paradoxically, that is exactly the technique recommended in the CubCrafters SS Titan manual (O-340 with carb and electronic ignition):

Titan_340CC_1.09.15.pdf (I'm not trusted to post a full URL)

para 3.5.4 -

"4 Mixture (Without an EGT Gauge): The mixture should be slowly but deliberately leaned until engine roughness is noted. The mixture should then be enriched until the engine returns to smooth operation. The cylinder head temperatures should be monitored to ensure proper fuel/air mixture."

I don't have a position on this as one airplane I operate is 0-360 with carb and mags and the other is IO-360 with injection and electronic ignition. I lean the O-360 to the first sign of roughness then richen till it's smooth again. That engine has over 2.900 hours since overhaul. Most of the time the IO-360 is LOP and less than 60 % power just chugging along enjoying the view.
 
You should read their engine service manual. It references timing the mags and lots of other pages plagiarized right from the Lycoming overhaul manual that directly contradicts what you are looking at. Tribal knowledge ;)
 
"4 Mixture (Without an EGT Gauge): The mixture should be slowly but deliberately leaned until engine roughness is noted. The mixture should then be enriched until the engine returns to smooth operation. The cylinder head temperatures should be monitored to ensure proper fuel/air mixture."

I don't have a position on this as one airplane I operate is 0-360 with carb and mags and the other is IO-360 with injection and electronic ignition. I lean the O-360 to the first sign of roughness then richen till it's smooth again. That engine has over 2.900 hours since overhaul. Most of the time the IO-360 is LOP and less than 60 % power just chugging along enjoying the view.
My IO-360 with balanced injection and electronic ignition never gets rough when leaning. It just gradually loses power as the mixture is leaned, remaining smooth the entire time.
 
I have chronicled my data in this thread. Result of a customer leaning his Carbon Cub SS in cruise flight how he had done his old Cessna for years and ended up burning an intake valve. Bobby Loper at ECI was a good source on the ignition and leaning conclusion.

Steve, great thread and thanks. Nice to get some in depth info on the care and feeding of a Lightspeed ignition and what can happen with its use etc.

Short but to the point story on an intake valve failure of a bit larger proportion but just points out how much a bad intake can affect an engine. Pretty much apples to oranges engine wise but similar results. It’s just an engine after all.
Dead of winter about 1978 or so…C-46 tanker delivering heating oil 2K gallons a pop along the lower Yukon. Our old high time pilot Bob Rice in cruise but setting up for landing in Galena, done for the day. Cold, probably -30 or so, getting close to entering downwind and starts power reduction for gear extension. Gear still in the well when #1 (R-2800) backfires so violently it belches whitish blue fire out the intake scoop that reaches as far forward as the rear cockpit windows. That’s about 6-8 feet. Not once but at least 6 or more times so fast it was like a machine gun. Only quit when Bob pulled the throttle back in a huge power reduction. Gear down, mostly routine landing from there but engine definitely not doing much at that point. Airplane parked, called the boss, mechanics dispatched (myself and the bosses son).
Took some investigation but end results were: #8 (master rod cylinder) zero compression due to intake valve head missing, valve stem punched through the top of the head between the two valves, massive hole in the piston where the valve head had exited into the crankcase. Garbage engine, all in less than about 30 seconds. The interesting part, as was the case with the CC 340 engine, was the complete multiple ignition event of what amounted to the entire intake charge for the entire engine at once, in rapid succession, though the valve head wasn’t gone on the Lycoming and much less being ignited. Interestingly, while that was going on, it was also torching out of the crankcase breather line (1”) and burning a nasty spot on the tire that was just coming out of the wheel well. Got it hot enough to crispy a spot enough we had to change that tire also. Intake system compromised: definitely not a small problem. I’ll take a “routine” toasted exhaust valve any time over that.

Cheers, Mike
 
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