Backfire During Runup

Mooney Fan

Mooney Fan

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Mooney Fan
Purchased a 67 Cherokee 140 last week. Put about 8 hours on it, and still getting used to starting on the left mag, as all other planes I have flown are started on both. Well, I didn't switch to both after start and taxied to the run the active. Then of course it happened...... When I went what should have been 2 over to check the right mag, I actually went 2 over and turned off the ignition. I immediately went back to both and got a backfire. Since then I have put 2 hours on the plane with no adverse effect.

Some have suggested I have the baffles inspected. Just wondering if anyone has any input on this.

Thanks
 
Curious, why do you start on one mag? I'm flying one a few years younger ('76) and we start on both.
 
Might want to talk to an A&P about impulse couplers and starting procedure. I doubt that I'd bother with starting on one mag just because it had the impulse coupler.

Edit: If the other mag needs to be off for start then it's prolly grounded by the starter switch.
 
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Mooney Fan said:
Purchased a 67 Cherokee 140 last week. Put about 8 hours on it, and still getting used to starting on the left mag, as all other planes I have flown are started on both. Well, I didn't switch to both after start and taxied to the run the active. Then of course it happened...... When I went what should have been 2 over to check the right mag, I actually went 2 over and turned off the ignition. I immediately went back to both and got a backfire. Since then I have put 2 hours on the plane with no adverse effect.

Some have suggested I have the baffles inspected. Just wondering if anyone has any input on this.

Thanks
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Usually it's an after-fire, and not a back-fire when you do that... and the exhaust system takes the punishment...

On the Piper stuff, the flame arrestor things inside the exhaust crack and then if not caught, usually fall out of the aircraft someday later in-flight. :)
On Cessna stuff, usually a quick check for cracks and that's about it.

Couldn't tell ya what's usually checked on Mooney stuff. But just a mini-list to show it's usually not too much of a big deal... tell the mechanic you caused an after-fire by turning the mags off and back on, and heard a bang, and they'll check what needs to be checked... shouldn't take much time at all.
 
Good lord, you said Cherokee and I read Mooney... I think the late nights this week are getting to me. :)
 
denverpilot said:
Good lord, you said Cherokee and I read Mooney... I think the late nights this week are getting to me. :)
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Yeah, my screen name did that.... Even though I own a Cherokee, the Mooney I rented for a couple years made me a huge fan
 
denverpilot said:
Usually it's an after-fire, and not a back-fire when you do that... and the exhaust system takes the punishment...

On the Piper stuff, the flame arrestor things inside the exhaust crack and then if not caught, usually fall out of the aircraft someday later in-flight. :)
On Cessna stuff, usually a quick check for cracks and that's about it.

Couldn't tell ya what's usually checked on Mooney stuff. But just a mini-list to show it's usually not too much of a big deal... tell the mechanic you caused an after-fire by turning the mags off and back on, and heard a bang, and they'll check what needs to be checked... shouldn't take much time at all.
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Good idea. I will give him a shout tomorrow
 
flow many a Cherokee, never heard of starting on one mag but what they bleep do I know.
 
I don't recall if there's a good reason to have only the mag with the impulse coupling active during start... the other mag isn't doing much until the RPM is high enough for it to fire, anyway.

Somewhere in the back of my head, I seem to recall that teaching only to have one mag on during start caused a bunch of this to happen (people going to OFF during the run-up) and the consensus was that there was no particular reason to not have them both on during start, anyway... it was just written up that way to remind the pilot that if the impulse coupling or left mag failed, you probably couldn't get it started at all.

Buuuuuut... I could be wrong here. Just seems like I recall that it doesn't matter from somewhere and the primacy problems with learning it as BOTH were triggering problems when people only used LEFT.

Might ask your mechanic what they think of just starting it in BOTH if that's what you're used to... or do some web searching... don't take this Internet dude's word for it. :)
 
eman1200 said:
flow many a Cherokee, never heard of starting on one mag but what they bleep do I know.
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Likely you have always started on one mag. Most modern Cherokees (Archer II, Warrior II etc.) have an ignition switch that grounds out the non-impulse mag when in the "start" position. Release the key switch and the run position of the key fires both mags for you.

-Skip
 
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Skip Miller said:
Likely you have always started on one mag. Most modern Cherokees (Archer II, Warrior II etc.) have an ignition switch that grounds out the non-impulse mag for you. Release the key switch and the run position of the key fires both mags for you.

-Skip
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correct
 
denverpilot said:
I don't recall if there's a good reason to have only the mag with the impulse coupling active during start... the other mag isn't doing much until the RPM is high enough for it to fire, anyway.

Somewhere in the back of my head, I seem to recall that teaching only to have one mag on during start caused a bunch of this to happen (people going to OFF during the run-up) and the consensus was that there was no particular reason to not have them both on during start, anyway... it was just written up that way to remind the pilot that if the impulse coupling or left mag failed, you probably couldn't get it started at all.

Buuuuuut... I could be wrong here. Just seems like I recall that it doesn't matter from somewhere and the primacy problems with learning it as BOTH were triggering problems when people only used LEFT.

Might ask your mechanic what they think of just starting it in BOTH if that's what you're used to... or do some web searching... don't take this Internet dude's word for it. :)
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Not sure if my switch says 'both or 'start'. Will verify
 
Skip Miller said:
Likely you have always started on one mag. Most modern Cherokees (Archer II, Warrior II etc.) have an ignition switch that grounds out the non-impulse mag for you. Release the key switch and the run position of the key fires both mags for you.

-Skip
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Just for your fund of trivial knowledge, the turbo Dakota has impulse couplers on both mags. Starts on second or third blade nearly every time when cold.
 
Clark1961 said:
Just for your fund of trivial knowledge, the turbo Dakota has impulse couplers on both mags. Starts on second or third blade nearly every time when cold.
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Thanks for that information. If I am correct, the Dakota has the O (or is it the IO?) 540 engine. Why this leads to a different mag wiring .... :dunno:
 
Skip Miller said:
Thanks for that information. If I am correct, the Dakota has the O (or is it the IO?) 540 engine. Why this leads to a different mag wiring .... :dunno:
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Dunno 'bout the Dakota engine. The turbo Dakota has the TSIO-360-FB from the factory.
 
mscard88 said:
Curious, why do you start on one mag? I'm flying one a few years younger ('76) and we start on both.
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Because your PA-28 0-320 has but 1 impulse coupling, meaning only 1 mag will be retarded during start. You start on the mag with the impulse coupling, simply because the other mag may fire at 25 degrees before top dead center and the engine will kick back on the starter bendix. That's a bad thing.
 
Post #1says PA-28-140, that is not a Dakota, it will have a 0-320- E2?, which has 1 mag impulse coupling on the left mag the right one is not grounded during start. ( as originally equipped)
 
I start my 1965 cherokee 140 on the left mag as well.
 
CC268 said:
I start my 1965 cherokee 140 on the left mag as well.
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you just start it. it's rigged on the left mag, but you don't 'select' the left mag, that's where I was going with that.
 
eman1200 said:
you just start it. it's rigged on the left mag, but you don't 'select' the left mag, that's where I was going with that.
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Na I start mine literally with the key on left mag and then press the button and bam. Maybe I’ve been doing it wrong the past 130 hours?? Just doing what my checklist says
 
CC268 said:
Na I start mine literally with the key on left mag and then press the button and bam. Maybe I’ve been doing it wrong the past 130 hours??
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hhmm, so you DO select left mag? ok, I'll shut up now, apparently I know nothing about starting a Cherokee.
 
eman1200 said:
hhmm, so you DO select left mag? ok, I'll shut up now, apparently I know nothing about starting a Cherokee.
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Yep. Select left mag. But keep in mind my panel was completely redone so in 2010 so it may not be the same as original...
 
CC268 said:
Na I start mine literally with the key on left mag and then press the button and bam. Maybe I’ve been doing it wrong the past 130 hours?? Just doing what my checklist says
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Key to the whole thread is bolded, emboldoned....is um... darker than the rest of the words. If you ain't got no button, you ain't gotta worry bout which mag the engine starts on.

<--- no button 1969 Cherokee 140
 
eman1200 said:
hhmm, so you DO select left mag? ok, I'll shut up now, apparently I know nothing about starting a Cherokee.
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Separate momentary push button to activate the starter, not a "start" position full clockwise on the magneto key switch which automatically grounds the right mag. That's why the mag switch must be in the " left" position on starting.
 
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