At 10:09 PM 6/13/99 -0400, Kirby T. Kenyon wrote:
>Atwell,
>
>I also have this problem with my '80 Spit (which has a '78 Carb). I have
>no catalytic converter. I'm curious why this problem might implicate the
>converter?
The converter is hot and will ignite unburned gas on overrun...ESPECIALLY
when an air pump is shooting air in to make the embers glow! Melted-down or
disintegrated cat elements will have hot spots that amplify the backfiring
tendancy.
Does your car have the air pump going into a single pipe in the exhaust
manifold, or into four small pipes on the cylinder head? In the latter
system Triumph fitted a 'gulp valve' whose function is to divert the air
pump flow to the atmosphere on overrun. My 5.0 Mustang V8 has a similar
system.
>
>Also, do you know if there are any problems from not using the air pump?
>I've put 2 used ones on the car since last fall. I hope that the last one
>will work OK but don't really want to spend the $ to get a new one.
>
>You always seem to know these answers.
<blush> I gotta say that I do THINK about these things a lot... and I tend
to over-analyze stuff very often!
Be that as it may, My Spit has the same tendancy to backfire if the air
pump is connected. (I know my Cat is shot because the PO's carb had a bad
jet and was running rich for gawd knows how long.)
I have plugged the air pump pipe just downstream of the check valve. The
air pump belt has been removed. I give it a spin once in a while to keep
the pump 'limber'. If need be I can restore it to 'operational' in 5
minutes (for our states smog check, for example).
I have run the car that way for about 3000 miles, with no apparent downside.
Bob Norway taught me this stuff last year. He has had this problem on
several Spitfires.
I'd say remove or disable the pump and don't worry about it. Just plug the
pipe so that exhaust gases don't cook the bearings in the pump.
Does your Spit have a header installed?
Atwell
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