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svanarts

Well Known Member
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 then 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?
 
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You say you just did your condition inspection. What did you all do? Something you worked on or adjusted may have been the cause. If you adjusted the timing, did you make sure you didn't time a mag before the impulse coupling triggered? You need to turn the prop beyond TDC, then back to 25 deg BTDC to properly adjust the mags. Did you get all the plug wires back to the correct cylinders? Are the plugs gapped correctly? Go back and recheck what you did to see if something is amiss.

Good luck,

Roberta
 
Make sure you have the plug wires correct. Sounds like you could have cross wired plugs.
 
I'd put my money on Mel's answer!

Mel said:
Make sure you have the plug wires correct. Sounds like you could have cross wired plugs.
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I was thinking maybe the backfire caused an intake leak but Mel's idea is WAY more likely.

And I see Roberta mentioned the same possibility.

Mark
 
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Good replies all. Everyone that I've talked to keeps pointing me back to the ignition system so that's where I'll start. This was a plain vanilla inspection, no adjustments were necessary, just cleaned the plugs and put them back in. I'll checked for crossed wires tomorrow when I go back. I'm really hoping it's something stupid like that. :)
 
4 cylinder monitoring

svanarts said:
Good replies all. Everyone that I've talked to keeps pointing me back to the ignition system so that's where I'll start. This was a plain vanilla inspection, no adjustments were necessary, just cleaned the plugs and put them back in. I'll checked for crossed wires tomorrow when I go back. I'm really hoping it's something stupid like that. :)
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Do you have 4 cylinder EGT/CHT monitoring? If you do, you could probably isolate a problem to a specific plug...

gil in Tucson
 
Check the plugs with a bright light and a magnifying glass. A tiny sliver of metal shorted out a new plug I installed. The sliver was about the size of a hair and very hard to see. It shorted the center electrode to a side electrode. Came that way on a new plug, seemed to be welded on.
 
Not sure if you have a baffel in your muffler but if you do always check it after a backfire. It can come loose and block your exhaust.
 
Just want to point out a couple of things

A "backfire" is when the fire goes backward. It's a fuel/air mixture being ignited in the intake somewhere.

An "afterfire" is when an fuel/air mixture is ignited in the exhaust.

The "afterfire" is normally louder than a backfire and sounds more like a shotgun.

I know this is getting picky. Most everyone calls an afterfire a backfire anyway. But for troubleshooting you sometimes need to know which one it is.

Someone correct me if I'm wrong here.

One more thing to mention, on the ignition leads, the caps that screw onto the spark plugs are marked T1, or T2 or B3 etc. It tells you what cylinder they go on! It doesn't really stand out and if no one has told you before you may not realize they are marked.

Mark
 
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If it has a carb check the venturi, I had a flight school plane that ilded terible . It had a backfire /carb fire and melted the aluminum venturi.. it idled as you described.. I canged it and it was AOK
 
kevinsky18 said:
Not sure if you have a baffel in your muffler but if you do always check it after a backfire. It can come loose and block your exhaust.
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Very few if any RV/ Lyc installations have mufflers.
 
If you can't find your problem following the other suggestions, you might check the gaskets on the intake tubes. A broken gasket can have symptoms like you suggest.

JT
 
MYSTERY SOLVED

Give Stephen a cigar. :)

Here's what happened:

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 the electrode gaps and shorted the plugs out. Luckily my friend could see it. We 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!

Thank you everyone for your suggestions!
 
Mark Burns said:
A "backfire" is when the fire goes backward. It's a fuel/air mixture being ignited in the intake somewhere.

An "afterfire" is when an fuel/air mixture is ignited in the exhaust.

The "afterfire" is normally louder than a backfire and sounds more like a shotgun.

I know this is getting picky. Most everyone calls an afterfire a backfire anyway. But for troubleshooting you sometimes need to know which one it is.

Someone correct me if I'm wrong here.
Click to expand...


Mark is right. If you had a backfire, the damage will be in the intake and most commonly in the carburetor. If it was an afterfire, the damage will be in the exhaust. Not being sure which it was, you need to check both. In either case, the likely cause in this situation was a mis-timed mag. The most common cause of a true backfire is the mixture being not rich enough during a start sequence.

Walter
 
svanarts said:
Give Stephen a cigar. :)

Here's what happened:

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 the electrode gaps and shorted the plugs out. Luckily my friend could see it. We 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!

Thank you everyone for your suggestions!
Click to expand...

:eek:
This scares the heck out of me for a different reason - FOD in the cylinder due to transporting abrasive on the spark plug! GOTTA check 'em to make sure they are clean!
 
I clean the plugs with mineral spirits followed by lacquer thinner before I blast them in the spark plug cleaner. This will remove any oily residue that might help the grit get stick up around the porcelein. After grit blasting they get blown out and recleaned in lacquer thinner and blown out some more. You definately do not want that grit in your engine.

Another point is I use the iridium, fine wire electrode, plugs. They are much easier to clean and adjust.

Glad you found the cause.

Roberta
 
HF grit

robertahegy said:
.....

After grit blasting they get blown out and recleaned in lacquer thinner and blown out some more. You definately do not want that grit in your engine.
....

Glad you found the cause.

Roberta
Click to expand...

I too have had this happen with the Harbor Freight plug cleaner supplied grit. It jams in there and will not solvent wash out or blow out.

A good visual inspection with a strong light is needed.

I solved the problem by switching to glass beads that are a much smaller diameter.

This is a caution for all purchasers or the HF plug cleaner

- buy new abrasive media!! You certainly don't want any of it transferred to your cylinders.... :eek:

gil in Tucson - I was lucky... I found it before the plug was reinstalled
 
Mostly irrelevant musings

Silicon carbide (SiC) abrasive is very sharp and very hard. It is also electrically conductive. (I don't know how I remembered that!) I imagine that it would severely erode the porcelain on a spark plug if used in a blaster. Aluminum oxide is not as hard or as sharp as SiC, nor is it conductive. I have used both in optical work. I wouldn't use either of them in a bead blaster unless I was working on a rusty steam locomotive. I think my plug blaster uses glass beads. Don't breath the dust! I doubt that a stray grain or two of Carbo, Alumina, or glass in a combustion chamber would hurt an engine. It would probably get blown right out through the exhaust. This discussion might justify one of those combination flashlight/magnifying glasses for inspecting plugs, hmmm? As someone recently said here, women buy jewelry, men buy tools. BTW, ATS is having a sale.
 
This may be common knowledge but was a surprise to me. An automotive engine re-builder explained to me you should never use petroleum solvents to wash a part that has been glass beaded. He said the microscopic glass that is left behind impregnates itself in the steel, aluminum, or cast iron part. Hot soapy water is the preferred way to get rid of any traces of the glass bead. Supposedly the petroleum solvents help the abrasive material stay attached to the cylinder walls and other parts which causes premature wear. This was a fairly large and successful business. Any other opinions?
 
Jeweler's loupe....

Hi guys,
Many of the NASCAR guys have jeweler's loupes........that little magnifier the cross-eyed jeweler uses to carefully look at your trade-in... :D . It's a ten power magnifier and you can count your fingerprints easily. Check out a jeweler's supply or even a jeweler for a source. I've seen Darrell Waltrip use one checking spark plugs.

Regards,
 
I've kept a jeweler's loop in my tool box for decades. It comes in handy more often than you would expect for more than just looking at spark plugs! You can get them in 10x and 20x. I've found the 10x works best for me.
 
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