Backfire?

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Hawaiis0
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Backfire?

Post by Hawaiis0 »

Hi everyone. What causes back fires into the air box?
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Pete Boole
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Re: Backfire?

Post by Pete Boole »

Timing usually.

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rbgosling
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Re: Backfire?

Post by rbgosling »

Or possibly inlet valves that are worn/broken or not closing fully for some reason.
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Re: Backfire?

Post by bash »

Id go timing too, mixed up plug leads, distributor cap tracking or the infamous rotor arm.
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MetBlue
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Re: Backfire?

Post by MetBlue »

Another cause is juvenile motorbike fun.
Drive down a straight road. Kill the ignition by the switch Japanese manufactures always thoughtfully put on the handlebar grip. A couple of good twists of the throttle. Switch ignition back on.
Now watch the people on the pavement jump as a satisfying 'bang' - and occasionally a flame exit the exhaust 😀
Oh what memories.
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rbgosling
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Re: Backfire?

Post by rbgosling »

MetBlue wrote:
Mon Apr 18, 2022 12:33
Another cause is juvenile motorbike fun.
Drive down a straight road. Kill the ignition by the switch Japanese manufactures always thoughtfully put on the handlebar grip. A couple of good twists of the throttle. Switch ignition back on.
Now watch the people on the pavement jump as a satisfying 'bang' - and occasionally a flame exit the exhaust 😀
Oh what memories.
Tony
Ah - but that causes a backfire through the exhaust! Fill the exhaust with unburnt gasses, then ignite them.

Another good way to get a backfire through the airbox is to convert to LPG. I had an LPG-converted Subaru that used to do that randomly, scared the bejeezus out of me the first few times.
"Farmer" Richard

1990 Lotus Excel SE (Lilith)
2022 MG MG5 EV (not due to be a classic for quite a few years...)

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Hawaiis0
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Re: Backfire?

Post by Hawaiis0 »

I now believe the correct term is SPITTING.

I will go with timing and associated parts first.

Thanks
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Re: Backfire?

Post by Marten »

rbgosling wrote:
Mon Apr 18, 2022 12:49

Another good way to get a backfire through the airbox is to convert to LPG. I had an LPG-converted Subaru that used to do that randomly, scared the bejeezus out of me the first few times.
Lean mixture will burn so slow it is still burning when the intake valve opens again. This works best with a fuel injected engine with a large plenum, but you can also melt a nice pair off double barreled Solexes

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