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Old 10-20-2019, 01:43 PM
n518jh n518jh is offline
Join Date: Jan 2015
Location: Sun City West, AZ
Posts: 41
Default Run Up drops of 140-200 RPMs

Lately I have been having trouble starting my RV-12 (2009 Engine delivery). My mechanic seems to think it is bad Ignition Modules. I had a soft start since the beginning, now 400 hrs. The current soft start went bad (didn't start when installed, started when disconnected.)

In the last set of start ups, the drops when A only or B only were 200 and 130 respectively. Would that support the thought of bad ignition modules, or should something else be tried before ordering new? Help please, those new modules are apparently expensive. Mark 518JH

Last edited by n518jh : 10-20-2019 at 01:45 PM.
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Old 10-20-2019, 03:36 PM
NinerBikes NinerBikes is online now
Join Date: Dec 2018
Location: Granada Hills
Posts: 757

If it starts and runs, and then at 4000 rpms, you are seeing those kind of rpm drops instead of 80 to 90 rpm, for each, I would suspect something in the ignition system. Go through each item in the ignition system, one by one, until you eliminate the problem.

Capacitors, condensers, spark plug wires, and new plugs are where I would first check. Last would be ignition modules.
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Old 10-20-2019, 05:16 PM
Piper J3's Avatar
Piper J3 Piper J3 is offline
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,025

Maybe this...
Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 610

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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Old 10-20-2019, 09:22 PM
RFSchaller RFSchaller is offline
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,792

As I recall ROTAX allows up to 300 RPM drop with a delta of 115 RPM, so your numbers would be within limits, but in almost 1000 hours and 7 years I have never seen greater than 100 RPM drop and a delta of 50 RPM.
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Old 10-21-2019, 10:29 PM
n518jh n518jh is offline
Join Date: Jan 2015
Location: Sun City West, AZ
Posts: 41
Default Erratic starting and large RPM drop

I will take your advices. Thanks. Will report on progress. The non start is the biggest problem.On advice I ran a hair dryer on the ignition modules and coils for about a minute, and the engine started, after several non start tries. Does that indicate anything? Once started it will restart with no problem.

Another comment was the in the 2005-8 years, a number of ignition modules were shipped that eventually caused non-start problems. Anyone have information on that perspective (my engine shipped in 2009), Mark
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Old 10-22-2019, 05:46 AM
Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,657
Default I ordered my kit day one

I had both ign modules fail between 400 - 500 hours. Back then they had a program where they would sell you two new YELLOW strip ones for much less than normal retail. Have 1,370 hours now. Not a problem again.
John Bender
Flying RV-12 - Serial #120036
Paid in May ( 5-2020 )
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Old 10-22-2019, 12:54 PM
Cammie Patch Cammie Patch is offline
Join Date: Oct 2018
Location: Boise, ID
Posts: 35

Those RPM drops are normal. At 4000, the engine is at it's leanest position. In the summer you will get less RPM drop, since the combustion is happier. In the winter, it would prefer more fuel, thus the higher drop.

Mag drop issues tend to point to carburetor issues more than ignition issues overall.
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