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IO-240 B4B: Rough idle and left mag drop

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FlyboyTR

Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama

Posted: Mon Jun 16, 2008 5:42 am Post subject: IO-240 B4B: Rough idle and left mag drop

My IO-240 now has 425 hours.  In the past it would only drop about 30 RPM on mag check at 1,700 RPM.  Even at idle speed there was almost no change in RPM, sound or vibration when switching from both to L or R mag.  It has always idled extremely smooth at idle on either mag.



Three weeks ago I noticed the engine was idling rough.  On the next flight, I had about 120-150 RPM drop on the left mag (at 1,700 RPM).  The roughness at idle has gotten worse.  At idle, the engine will almost die when switched to the left mag only...and sounds really ragged!



Here's what I have done so far:

Cleaned plugs, regapped to .019", pressure tested plugs, tested all eight spark plug leads, checked engine timing (off by 2.5 degrees), removed and inspected left mag.  No pitting or issues noted with points.  Reinstalled everything, timing set to within 1/4 degree ("B" series engine is 26 degrees).   I also removed the injectors (for good measure) and give them an hour in the ultrasonic parts cleaner.



Engine only drops about 100 RPM on left mag (at) 1,700 RPM (better) but still runs rough at idle and still will almost die when running only on the left mag at idle.  



I am at a loss at this point.  The plugs are still within their wear limits.  I have ordered new plugs (Champion RHM38E) just to rule out a plug issue...even though they pressure tested perfectly!



Your comments or suggestions would be sincerely appreciated.  Thanks!



Travis

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_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website)

RBartholomeee(at)comcast.
Guest

Posted: Mon Jun 16, 2008 1:23 pm Post subject: IO-240 B4B: Rough idle and left mag drop

The first thing to do is run the engine on the bad mag only and find the

cold cylinder.  If you don't have 4 temp gauges spray wd40 on the exhaust

pipes to find the 3 hot ones.  Then you can switch the plugs and even the

wires with one of the good cylinders.  If this doesn't help I would chech

the compression and look at the exhaust valve if it is low.



                         Roger (at) MD43  C150-E



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FlyboyTR

Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama

Posted: Mon Jun 16, 2008 6:20 pm Post subject: Re: IO-240 B4B: Rough idle and left mag drop

Roger,

Thanks for the reply.  I have full cylinder management.  There was less than 30 degrees between all cylinders while running on the left mag!  I tried at idle, 1200, 1700 & 2000 RPM.  I tried your suggestion prior to starting with the other stuff.



I was sure I could find a cold cylinder.  However...I have not checked for compression loss......not sure why!  On my last annual in September, all were 78/80.  



Travis

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_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website)

RBartholomeee(at)comcast.
Guest

Posted: Tue Jun 17, 2008 3:40 am Post subject: IO-240 B4B: Rough idle and left mag drop

Btw I had a hell of a problem like you did and couldn't find it with my

installed analog exhaust gas temp.  The plugs checked out under pressure

testing and we finally put know good plugs in the cylinder and it fixed the

problem.



                   Roger



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FlyboyTR

Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama

Posted: Tue Jun 17, 2008 3:44 am Post subject: Re: IO-240 B4B: Rough idle and left mag drop

I believe that new plugs (even thought the old ones checked out fine) are my next step.  I will also check the compression at the same time.  Good suggestion.  Thanks again.



Travis

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_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website)

FlyboyTR

Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama

Posted: Sun Jul 06, 2008 7:12 am Post subject: Re: IO-240 B4B: Rough idle and left mag drop

I installed new Champion spark plugs, gaped to approximately .018".  I also readjusted the idle speed fuel pressure per the new Service Bulletin.  The engine is certainly running better, but still a little rough on just the left mag at idle and slightly more RPM drop at mag check at 1,700 RPM than the right mag...but better overall.



At this point I believe I will run it until I get another noticeable change.  Thanks to everyone for the suggestions.



Travis

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_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website)

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