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01-24-2015, 05:33 AM
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Join Date: Nov 2013
Location: Tampa, FL
Posts: 20
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Engine back firing
Got me stumped. After cleaning plugs and re installed them ran the engine everything was fine. Flew it one hour, stop for gas, started then did my run up before take off. 1700 rpm check my cs prop, ok. Switched of right mag drop off 75 rpms , then the left drop of 125 rpm at started back firing, turned back on rechecked the right again a 75 rpm drop then after a second it back fired. Repeated process once again same results. Ran the engine on both Mags to 2400 no back firing back to 1700 no issue with both mags but does occure on one mag. Any suggestion were to start and what sequence to start. Thank you in advance for any help.
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01-24-2015, 05:36 AM
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Join Date: Jan 2005
Location: SC
Posts: 12,887
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Since you "just cleaned the plugs*, I would check to make sure you didn't cross the wires.
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Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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01-24-2015, 05:37 AM
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Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,271
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First of all did you do this mag check full rich or leaned aggressively? Do you have an engine monitor with data logging.
Could be mag issues, or more likely plug issues. How old are the plugs, and when were they gapped and resistance tested last?
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David Brown
DYNON Authorised Dealer and Installer
The two best investments you can make, by any financial test, an EMS and APS!
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01-24-2015, 05:51 AM
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Join Date: Jul 2010
Location: Orlando, FL
Posts: 1,077
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Similar problem on my O-360...
Misfiring on one mag, combustion in exhaust pipe, aggressive leaning usually cleared it. A friend with a very, very good eye looked at the plugs and said "I think this may be the problem." All plugs looked the same to me, but I changed that one. Problem went away.
YMMV.
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Chris Smith
Maule M5-180C (Sold)
RV-6 O-360 CS (Sold)
RV-4 O-360 FP (Sold)
Full-time in the other type of RV....
Last edited by ccsmith51 : 01-24-2015 at 08:12 AM.
Reason: Changed backfiring to misfiring...
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01-24-2015, 06:18 AM
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Join Date: Aug 2007
Location: Carrollton, GA
Posts: 313
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Maybe check to see that you didn't accidentally get some anti-seize on one of the plugs. I did that once and caused problems.
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Jim Brown
RV6, Christen Eagle II(Sold)
ATP, CFII, A-IGI, A&P/IA
Carrollton, GA
Lyon?s Landing
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01-24-2015, 07:35 AM
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Join Date: Jan 2007
Location: Stuart, FL /Hartford, CT/Virgin Gorda,BVI
Posts: 3,122
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here is my thoughts. take off and climb out over the airport. then do another mag check and see if the mags are ok. go from there.
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Ed D'Arcy
RV6-A 5,200+ hrs, R-44 1,600 hrs, Helicycle 320 hrs, gyro sold,35,000 miles flown in 2015 
Stuart, Fl / S WINDSOR,Ct / Virgin Gorda, BVI - under major repair from hurricane damage
VAF #840 EAA AOPA FAC FABA QB SPA
addicted pickle ball player
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01-24-2015, 07:53 AM
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Join Date: Mar 2005
Location: DVT Phoenix
Posts: 1,187
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You might check to see if after cleaning and flying, a small piece of carbon didn?t flake loose and lodge between the electrodes on one plug. Have seen this happen before. Just a guess but-------------
Larry
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01-24-2015, 08:07 AM
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Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
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And, is it truly a backfire (combustion coming out the intake), or just a miss? If it's just missing while running on one mag, I'd also vote for fouled/defective plug or harness issue, as 1st line of attack.
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01-25-2015, 05:46 PM
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Join Date: Nov 2013
Location: Tampa, FL
Posts: 20
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Big thanks to all
Will try all that has been suggested. The plug wires are set in a manner I believe would be difficult to get wrong, however I would say it could never happen. I"ll check. Remove plugs and really inspect them closely. Thank you again to all for the advise.
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01-27-2015, 07:27 AM
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Join Date: Oct 2012
Location: Scottsdale, AZ
Posts: 150
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I use SavvyAnalysis to do periodic checks on my engine health. Uploading and viewing your data is free, but they charge a yearly fee if you want them to have someone look at it for potential problems. They do give a lot of good information on what to look for yourself though. Here is some info on doing an ignition stress test https://www.savvyanalysis.com/articl...ht-diagnostics
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