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Keldog

Member
Strange thing happened twice now when shutting down from a flight. Idle in towards hangar after taxiing at about 2000 rpm's for 2 minutes, idle back to 1800 rpm's before shutdown, then off avionics, off Ignition A, off Ignition B, off master. Instead of immediately coming to a halt as normal, the engine continued to stumble on very roughly. Not sure what to do, I pulled the choke out and it finally rotated to a stop. First time it did it about 3 weeks ago, I thought maybe bad ground on one of the ignitions. So I took off the top cowl, checked all the connections on both modules and followed ground wires to eventual source to confirm all is tight. All good. Taxi to run up to check for normal rpm drop/delta of both ignitions; all good. Flew since first instance 4 times now with no more issues on shut down. Sunday flew to KTVL for breakfast with the better half and again....stumble on shut down; had to engage choke to get it shut down. After breakfast, started up fine, flew back home, same issue on shut down at home hangar.

Instinctively; I think I know what you guys are going to tell me to do; but thought it best to describe in detail what I experienced first.

Advice and direction is greatly appreciated!
2011 RV12 # 120201 395 hours
 
Sounds like one of the CD ignitions is not shutting off. Could be bad panel switch or intermittent connection to main panel.

Try shutting off one ignition at a time in cruise flight. You should notice a reduction in RPM when each ignition is shut off.

Try shutting down engine ignitions instead of A then B - try B then A.

Try shutting Master Switch off then shut ignitions per above...
 
My RV-12 experienced an intermittent internal failure of one of the panel-mounted ignition switches. It is a relatively easy fix with a new switch being available from Van's.
 
I believe your idle speed should be set to 1650 rpm or less.

I turn off one ignition system at a time, with throttle set at the idle stop.

This makes the shut down of rotation of the prop much less violent when the rotation stops through the gear box.
 
What spec are you using as a reference for the 912ULS? If idle speed is too low it is hard on the gearbox and causes wear.

You are correct, uneven firing pulses at low speed is bad for the gearbox. Yes, set idle for ~ 1600 so engine can be slowed sufficiently in the air for good aerodynamic braking when prop is being back-driven in a glide. When engine is being back-driven the gear mesh is loaded heavily in one direction and gears run smooth. As airplane touches down the pilot must advance throttle to operate in green arc on the ground. Gears and rotating elements (bearings) can take a lot of abuse if rotating at high speed. Envision wheel bearings on a car hitting a huge pot hole. As long as wheel in rotating, rollers/ bearing race are OK. Now hit a bearing with hammer during installation and you have added small flats on the rollers and bearing will fail.

I start and warm my engine at ~ 2700 RPM so that initial uneven running of cold engine appears smooth for the gearbox. My shutdown procedure is idle slightly above 2000 RPM when switching off ignitions. Engine has over 600TT and gearbox is like new. Relative “health” of gears and drive dogs on overload clutch can be “inspected” by feel and sound when burping the engine for oil level check. Turn the prop slowly and feel for backlash in the drive dogs when compression goes over TDC. Also rock the prop back/forth to feel gear mesh. Make a good mental picture for future comparison.
 
Operator's manual

You might want to read the operator's manual and see what it says about dieseling and proper shut down procedure. I have not looked at the procedure lately so I can't remember the instructions. The idle on my engine is set about 1600-1650, but I don't ever operate that low. Try not to let it get below 1950revs at any time. My shut down procedure is to reduce idle to 1950 momentarily, then back to min idle and quickly shut off one ignition, watch for rpm drop, and quickly shut down second ign. Engine temperature and fuel quality/octane can also cause run-on/dieseling.
 
My experience - -

I had the same thing 2 - 3 years ago. Finally found the small connector with the two 'kill' wires must of had a little corrosion. Put electric cleaner spray on connector halves. Then dielectric grease. Fixed it. Simple to try.
 
Thanks for the responses guys. A few answers to questions raised and another question:
JBPILOT and DHEAL - I think you're both talking about the same thing.(?) Is access for the switches from the front instrument panel or from the top through the avionics bay?
DBRuth and RFScaller - plane doesn't run hot and what is dieseling? I run 91 octane mogas 90% of the time and 100LL cross country. Occasionally i suppose I could have up to a 50/50 mix of the two in the tank as well.
Piper J3 - I will try the 3 tests in your reply from yesterday.

And here I thought all responses would point me towards the dreaded floats!
 
Carb floats are far down the list. Dieseling is when an engine continues to run (stammer) when ignition is shut off. This happens usually because of carbon build up in combustion chamber and hot carbon continues to ignite fuel haphazardly. I doubt very seriously if this is your problem. I have never heard of dieseling in Rotax engines.

Your problem points to ignition not shutting off well…
 
I doubt it is dieseling -- it sounds more like an electrical issue. As I recall (it's been a while back), I replaced my ignition switch by removing the ignition/starter switch panel while sitting in the left seat. You can then remove the errant switch from it's push-in connections on the module. It is easier to mechanically release the defective switch from the module if you break off the tiny locking tabs on the defective switch that hold the switch body in place. The replacement switch can then be snapped into place.

Alternatively, you could remove the avionics cover panel for a bit easier access but I did not find that to be necessary.
 
Many (most?) RV-12s have a faston splice in the ignition wires on the forward side of the firewall.
I think that is what JBPILOT was referring to.
Find those splices, unplug and plug together those connectors several times to wear away corrosion.
Apply grease and plug back together. The splices should not pull apart easily.
Turn the ignition switches on and off several times to wear away any corrosion on the contacts.
 
It should be easy enough to test the switch with a multimeter to verify if that is the problem.
 
Dieseling

Hello

I had the very same issue in Italy I get bad Benzina.
The engine run up was not smooth the full power for taking off maximum 4800 and going down and oil and weather get hot. Abort the teak off and taxi back.
If I shut down the engine it stops not as usual. The engine slows down as a big continental.
We searched the whole Sunday. In the end we changed the 20 gallons to a good quality of Benzina.

Daniel, Switzerland

RV12 670 real flight hours
 
Joe described what I was commenting on - -

The connector I was suggesting is under the top engine cowl on the legacy RV-12. White plastic as I recall.
 
Strange thing happened twice now when shutting down from a flight. Idle in towards hangar after taxiing at about 2000 rpm's for 2 minutes, idle back to 1800 rpm's before shutdown, then off avionics, off Ignition A, off Ignition B, off master. Instead of immediately coming to a halt as normal, the engine continued to stumble on very roughly. Not sure what to do, I pulled the choke out and it finally rotated to a stop. First time it did it about 3 weeks ago, I thought maybe bad ground on one of the ignitions. So I took off the top cowl, checked all the connections on both modules and followed ground wires to eventual source to confirm all is tight. All good. Taxi to run up to check for normal rpm drop/delta of both ignitions; all good. Flew since first instance 4 times now with no more issues on shut down. Sunday flew to KTVL for breakfast with the better half and again....stumble on shut down; had to engage choke to get it shut down. After breakfast, started up fine, flew back home, same issue on shut down at home hangar.

Instinctively; I think I know what you guys are going to tell me to do; but thought it best to describe in detail what I experienced first.

Advice and direction is greatly appreciated!
2011 RV12 # 120201 395 hours

Are you buying a good, FRESH, name brand, known quality of Premium unleaded Mogas, not the old stuff down at the local Mom and Pop store? Old fuel loses it's octane rating rather quickly. Try to buy from a gas station that does a lot of volume in sales of gasoline.
 
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