engine mis-fire during idle

Dan Thomas said:
We don't set points gap. We set the points to open at the E-gap, which gets them opening at the rotor position that gets the hottest spark. Anything else is less than ideal.
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Yup, you set that with a E-gap tool. Its still gets set, its still something to look at. Your point?
 
wilkersk said:
Yup, you set that with a E-gap tool. Its still gets set, its still something to look at. Your point?
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Some mechanics have used a feeler gauge to set the points to .010" or whatever. Some mag manuals would mention a gap range so they'd do that instead of using the proper rotor locating tool, and the E-gap would be off. Weaker spark. Less bang for your buck. And if the points were pitted (they always are, if not new) the gap was really off if the feeler gauge was used.
 
Dan Thomas said:
Some mag manuals would mention a gap range so they'd do that instead of using the proper rotor locating tool, and the E-gap would be off. .
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So, what is good enough?
 
steingar said:
I flew a 150 for years and never had such an issue.
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Some percentage of the mechanics in the thread are saying these engines should run like crap as normal behavior, and I’m wondering why none of the airplanes I’ve flown with that motor ever did...

I’m with you. And I flew more than one.

Mysteries abound. :)

I’m not buying that we had great maintenance either, because these were the cheapest possible rentals at the time at an airport FBO about to go bankrupt.

Unless I got luckier than I ever thought renting that trash... and over the years since then, I’ve learned renting trash airplanes at the lowest price is a really bad idea.

We must have had a secret super mechanic working for peanuts on those things.
 
denverpilot said:
Some percentage of the mechanics in the thread are saying these engines should run like crap as normal behavior, and I’m wondering why none of the airplanes I’ve flown with that motor ever did...

I’m with you. And I flew more than one.

Mysteries abound. :)

I’m not buying that we had great maintenance either, because these were the cheapest possible rentals at the time at an airport FBO about to go bankrupt.

Unless I got luckier than I ever thought renting that trash... and over the years since then, I’ve learned renting trash airplanes at the lowest price is a really bad idea.

We must have had a secret super mechanic working for peanuts on those things.
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Oh, the OP said it "runs like crap"? Well, ....that changes everything!
 
Tom-D said:
So, what is good enough?
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Using the right tool and following the manual. I always had much better performance out of any airplane I maintained or repaired when I did that. And I spent lots of time fixing problems incurred by folks who didn't do that.
 
wilkersk said:
OK, let's take this head-on:

Valve: Easy to check. leak-down test-does it leak? Borescope: is it burnt?

Magneto Points: A little more work, but, take the cap off, pull the mag, look at the points. Are they burnt? Is the gap set correctly?

Spark Plugs: Clean and test. How do they look? What is the internal resistance under load (spark plug tester)? Any cracked insulators?

All easy things to check. And, by the way, stuff your A&P should be doing at least every annual. But, if there were problems with any one of these things you mentioned, I'd think you'll have different symptoms. Backfiring when reducing throttle usually points to an over-lean condition. Since you're saying it happens at idle, I'd suspect Idle-mixture. And, you can chase your tail a bit getting that perfect for every day. Hence my suggestion that you might prefer a slightly rich idle-mixture setting.
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"Valve: Easy to check." You really think it's just this simple? It's not.

The O-200's are notorious for sticking valves. There's a bit more to diagnosing potential valve issues that your leak down test, or looking for the color signs, or other, of a valve, or it's seat, with your borescope. Apparently you forget that the majority of those sticking valves are due to coking or lead fouling of the valve guides. He could very easily be experiencing the symptoms leading to that stuck valve you might find with your leak down test. And good mechanics know there's a lot more that can be added to this "leave it alone" discussion.
 
Art Rose said:
"Valve: Easy to check." You really think it's just this simple? It's not.

The O-200's are notorious for sticking valves. There's a bit more to diagnosing potential valve issues that your leak down test, or looking for the color signs, or other, of a valve, or it's seat, with your borescope. Apparently you forget that the majority of those sticking valves are due to coking or lead fouling of the valve guides. He could very easily be experiencing the symptoms leading to that stuck valve you might find with your leak down test. And good mechanics know there's a lot more that can be added to this "leave it alone" discussion.
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I don't think the OP is describing a valve issue.

What the OP said was that the engine "mis-fire every so often when close to idle." This sounds to me like the classic warm-engine, cold morning, lean condition. Harry Fenton probably described it best:

Harry Fenton http://www.bowersflybaby.com/tech/fenton.html#backfiring_at_idle
could be due to the onset of Fall and slightly lower outside air temperatures. When the outside air temp cools, the intake air density increases, therefore more fuel molecules are required to match the increased ratio of oxygen molecules. The carb idle mixture usually requires some minor adjustment from colder to warmer weather (and vice versa) to prevent backfiring, especially when the throttle is closed or when the engine is windmilling on an extended glide. Usually, the idle mixture is too lean if the engine pops a bit when the throttle is reduced when landing. The idle circuit is not effective above 1000 rpm, so the main metering jets take care of fuel flow and the engine is not likely to backfire when operating at higher engine rpm’s.
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wilkersk said:
I don't think the OP is describing a valve issue.

What the OP said was that the engine "mis-fire every so often when close to idle." This sounds to me like the classic warm-engine, cold morning, lean condition. Harry Fenton probably described it best:
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The vast majority of the O-200 valve stick failures occur when you power back in the pattern. I'm not saying that he is experiencing the beginnings of a stuck valve, but it's definitely a possibility. And it should not be ignored.

Too many experts here. I'm done.
 
wilkersk said:
Oh, the OP said it "runs like crap"? Well, ....that changes everything!
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Well nothing I own that “misfires at idle” wouldn’t be labeled “runs like crap” other than a cold two stroke weedwhacker... but call it whatever you like.
 
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