Rough running engine after backfire

svanarts · Post by **svanarts** » Sat Apr 14, 2007 6:54 pm

I'm not much of an engine guy so any advice would be helpful.

A little background first: this is an O320-D2A from Aerosport Power and has always run great. Has a standard MS carb and Slick Mags.

Today I started my engine after doing my annual condition inspection. The engine took quite a few cranks to get going. Then it backfired and started but ran pretty rough. Sounded like it was missing. I ran it for a little while but the roughness never left. I tried a run up and it still sounded rough. I did a mag check; ran REALLY rough like almost wanting to quit when I switched to the right mag. The engine didn't sound any different on the left mag than it did with both mags. Any ideas of what I can check? Did I break something?

Leighton · Post by **Leighton** » Sat Apr 14, 2007 7:06 pm

my experience with lycs is TVO-435's and HO-360's, which isnt much but i'll chip in my buck oh five anyway.

Check the easy stuff first.

Spark Plugs.

Failing that i would consider pulling the pushrods, check to see if they're bent. If the pushrods are bent it'll make the engine run like a chaff cutter.

While your there check the exhaust valves to see how much slop is in them.

of course it could be something even simpler again.

Leighton.

jim_geo · Post by **jim_geo** » Sat Apr 14, 2007 8:07 pm

Sounds like your mags are out of adjustment. Or perhaps the spark wires are not quite right.

svanarts · Post by **svanarts** » Sat Apr 14, 2007 8:55 pm

I've had other suggestions about checking the spark plug wires. They are pretty hard to get wrong on my plane but heck, I wouldn't put anything past me!

I'll be going out tomorrow afternoon to re-check the obvious things. Just weird how before annual the engine ran like a top but now it runs like a Model T. I'll double check the wires tomorrow after church.

Wicked Stick · Post by **Wicked Stick** » Sat Apr 14, 2007 9:05 pm

Scott,

Before you do anything, trace back your steps of the condition inspection.
Did you remove or change anything related to the ignition system ? (other than remove and clean plugs)

Also, how many hours are on the mags ? If it's over 500, It's pretty much the norm to remove them and inspect the points, and the impulse coupling, etc for wear.

It sounds to me like somethings either out of time, or not working properly.

Keep us posted.

svanarts · Post by **svanarts** » Sat Apr 14, 2007 9:34 pm

The engine and accessories only have 250 hours or so racked up. So everything is pretty much still new. I'm really hoping it was just something stupid and I forgot to hook something up. I'm going to get a second set of eyeballs out there tomorrow. I'll definitely check back in with what it was.

captain_john · Post by **captain_john** » Sun Apr 15, 2007 7:00 am

I have heard the same thing as WS about the mags. They can go belly up fairly early in the game. Having it happen at annual could be just a strange coinicedence.

Of course, check everything that you put your hands on first. Then start checking other stuff. But of course, you already knew that.

Good luck! Let us know what it was.

CJ

Wicked Stick · Post by **Wicked Stick** » Sun Apr 15, 2007 12:11 pm

I tried to suggest possible causes based on 6 plus years of ownership on a 1976 Grumman AA-1B and what my A&P IA has taught me over the years.

Not knowing how many hours you had on them, I just thought I'd share my experiences. Hope you find the cause is something simple, and it will be airworthy again soon.

svanarts · Post by **svanarts** » Sun Apr 15, 2007 10:56 pm

MYSTERY SOLVED

It was an ignition problem; specifically the spark plugs. When I cleaned them I used a friend's Harbor Freight spark plug cleaner. The abrasive material used in it is just large to jam between the electrodes on an aviation spark plug. And guess what... the abrasive material is conductive! I couldn't see it but a few little granules of this stuff wedged itself in my plugs and shorted the plugs out.

A friend and I spent about 15 minutes with a fine steel wire digging them out. When I reinstalled the plugs the engine fired up and ran great again!

So lesson learned, I'm buying a real-live aviation spark plug cleaner for my next condition inspection.

JohnR · Post by **JohnR** » Mon Apr 16, 2007 9:16 am

Scott,

Glad you found the problem! I guess the ignition related suggestions were at least heading you in the right direction. Thanks for posting your findings so we can all learn from it.

svanarts · Post by **svanarts** » Tue Apr 17, 2007 12:06 am

All the suggestions were absolutely helpful. I was really hoping the problem just something stupid and I was right!

dons · Post by **dons** » Tue Apr 17, 2007 11:16 am

I wouldn't call that one exactly 'stupid'. When I stare at two wires for 5 minutes and can't get my brain to see they are backwards, that's a stupid cause. You had to do some detective work and actually find something subtle that had gone wrong in the process, that's being careful and learning from something that didn't go quite as planned. Sharing it with the rest of us so we can learn as well is just plain professional.