At 03:04 AM 4/7/2000 , you wrote:
> Does anyone know what causes a backfire through the TB? I've got the
> 4bbl bolted onto my Dak and the sensors sort've hooked up. (Nothing
> permanent, just to get the engine fired up.) Anyway, after checking the
> readouts on the sensors I fired it up. It ran exremely rich for maybe
> 20-30 seconds or so, then started to level out. The temp came up a
> little bit and it went into closed loop; the computer seemed to be able
> to switch rich/lean to maintain stoich without any difficulty. I don't
> have the throttle cable hooked up yet, so I just moved the throttle
> linkage by hand. I never let the rpms get really high, but I noticed if
> I opened it slowly, it seemed ok, but if I snapped the throttle open
> relatively quickly like what might happen if you blipped the throttle, I
> would sometimes hear a pop inside the intake, which sounded like a
> backfire to me. Is it possible that the engine needed to warm up some
> more? (I think the coolant temp got up to about 150-160 or so.) Or
> could it be something else? I didn't push it; I had visions of this
> expensive work of art blowing off my engine and taking my hand with
> it. ;-) Speaking of which, how much power can a naturally aspirated
> intake backfire create? Enough to damage the TB?
Backfire through the intake is caused by ignition timing too far advanced,
plug is firing before the intake valve is closed. And as for power it can
create, several tons of force, almost the same amount it pushes on the
piston, depends on how much of the expanding gases get past the valve
before it closes. Shouldn't affect the TB unless it's a pretty severe
backfire, as it can bend the throttle plate in the TB. Backfire could also
be caused by an excessively lean condition - the fuel is exploding from the
massive temperature change when injected and drawn into the
cylinder. Contact with hot metal or a hot plug could set it off.
Mike
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