I think it's time to summarize this thread. I'm getting confused and
befuddled. %-/
At 07:52 PM 6/13/99 -0400, Sam Gentry originally wrote:
>We just got the 80 spit running and it works well EXCEPT: When we rev the
>engine and let it coast down it backfires and gets very rich. Works great
>if we eliminate the air pump. I would like to keep the
>emission stock if possible.
Suggested fixes for elimination the backfire while maintaining the
emissions equipment:
1. Replace catalytic converter
2. Replace carb bypass/deceleration valve if blanked off
3. Check operation of diverter valve (if present)
We then went on tangents regarding how the air injection system works. Two
types of systems are installed on our Spitfires: one using a
vacuum-operated 'diverter valve' and an air rail with four pipes to the top
of the exhast manifold. The other has no diverter and injects air through a
single pipe into the bottom of the manifold just above the Cat. Pictures
are on page 92 of the Vicky Brit catalog.
Both types use an air pump (which has a relief valve to prevent damage if
the line is restricted downstream), a check valve (which prevents exhaust
gasses from blowing backwards into the pump) and the various configurations
of plumbing and vacuum lines.
As far as disabling the air pump to stop the backfiring, the most quickly
'restorable' way is to remove the drive belt and plug the pipe downstream
of the check valve (at the manifold for air rail systems or at the check
valve for single pipe systems). I don't recall anyone reporting anything
bad from this (unless an increase in power can be considered bad). The
engines still pass idle-type emissions tests without the pump working.
Removing all this paraphenalia (and plugging all the resulting holes) saves
weight but could get us in trouble with states that inspect for the
presence of the equipment.
The catalytic converters are expensive and generics can't be fitted because
of the integral flange (and lack of space downstream). The failure mode is
a crumbling/disintegration of the ceramic honeycomb element inside the 'can'.
Bypass/deceleration valves for the carb are available but diverter valves
for the air injection system are not (at least from SpitBits).
Lastly, I want a ride on John Suchak's motorcycle! :)
++++++++++
Did I miss any important points?
Cheers to All,
Atwell Haines
'79 Spitfire
Succasunna, NJ USA
"How come Superman could stop bullets with his chest, but always ducked
when someone threw a gun at him?"
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