O200A Right Ignition System ROUGH!

[MBDiagMan]

Just got the plane together after annual. Before annual the left mag was losing about 150 RPM during runup check, but the right side would lose less than fifty. I found a bottom (Left mag runs the bottom) plug with a bridged gap, so that was explained.

We put four of the cleaned and tested plugs in the bottom and new plugs in the top. Timing on both mags was spot on.

Got it back together and fired it up last night. It now runs great on the left, but REALLY rough on the right mag.

In years of troubleshooting all sorts of things I have often found that trouble after working on something can often be solved by going back to the last thing you did. We didn't touch either mag beyond checking timing.

With new plugs for the right and not touching the mags, it would seem that this would leave the wires. Gonna check them tonight if my IA hasn't checked them during the day before I get there.

Anything not making sense?

Thanks for experience sharing.

 

[taters]

ya check the wires and make sure they are seated correctly and in the right place ...you could have a bad new plug (if it was dropped) usually one plug isnt enough to make it run REALLY rough though

 

[Dan Thomas]

ya check the wires and make sure they are seated correctly and in the right place ...you could have a bad new plug (if it was dropped) usually one plug isnt enough to make it run REALLY rough though

One bad plug, on one mag, on a four-banger, will be rough.

And yes, reversed leads will make it run really badly. Usually happens between adjacent plugs. The nuts are numbered and should be checked.

Dan

 

[MBDiagMan]

I ran down the firing order last night to ensure that there were no switched leads. Although I know for sure that I didn't drop one of the new plugs, they are not wrapped such that they would be totally protected if dropped while in the package, so the possibility of the shipper dropping them is indeed a factor.

Thanks very much for the responses. I'm anxious to pry myself away from the office and get out there to see what's up.

Have a good weekend.

 

[MBDiagMan]

You guys were right. It turned out to be a spark plug. It runs really sweet on either mag now.

Thanks very much for sharing your experience!

 

[BigBadLou]

Glad you found your problem. How did you actually discover it?
Normally, if one mag runs worse than the other, swapping plugs between mags can be a good indicator as to where the problem is. (for future reference to anybody who's got a similar problem)

 

[Howard Wilson]

Yup, new spark plugs can be bad. Had an IA once tell me " you can drop a plug twice. Once on the floor and once in the trash" ;-)

 

[MBDiagMan]

My IA took the new plugs to his tester and found the offender.

In response to Howard's comment, I did indeed drop one of the bottom plugs. I dropped it the second time in the trash, but then I pulled it out of the trash and used a three corner file to make a thread chaser. I ground the connector end off of it to ensure that no one ever tried to use it as a spark plug and put it in my toolbox.

The plane is annualled now, gone over with a fine tooth comb. Engine runs so sweet I can't believe it. The punishment now is that I have an ear infection and can't fly it. My IA offered to go up with me, but he's not a tailwheel guy. If I got spatially disoriented I am sure he could get us down and we could walk away, but the thought of the possibility of ground looping her is an ugly one.