Re: Ur-quattro's Deceleration valve?

[Wallace White <wallace@remdesign.com>]

Another car I've owned, with a less illustrious name than the ur-q, also
had a deceleration valve: a 1977 Mazda GLC. Allowed air to bypass the
carburetor when you lifted off the throttle. Mine was stuck in the
bypass setting, so I just plugged it. It backfired some on deceleration
but was otherwise fine. But I don't think I would remove a working
one--much less on a car you care about.

I've also heard these valves called anti-backfire valves, anti-afterburn
valves and something else... is it "gulp valve"? I heard they were
common on GM trucks for a while. It does indeed seem like a hack on a
fuel-injected engine.

- Wallace
  '87 5kcstq 150k

DeWitt Harrison wrote:
> 
> On Sun, 18 Oct 1998 00:32:07 -0400, Martin Pajak wrote:
> 
> >What does the deceleration valve do on the 1983 Canadian Ur-q do?
> >I am trying to clean up some of the unnecessary vacuum lines and was
> >wondering how important is it?  It sort of looks like a blow-by valve
> >except it's hooked up to the intake rather than before the turbo.
> 
> The valve prevents the dumping of unburned hydrocarbons at
> throttle closure. When you lift, the throttle shuts faster than the
> fuel distributor can back off on fuel delivery resulting in a momentary
> excess of fuel at the intake ports. The decel valve opens at that
> moment allowing unmetered air to enter the system to combust the
> extra petrol and, possibly, to allow the air metering arm to fall faster.
> 
> It is also yet another example of the band-aid, fix on top of fix
> widgets the Bosch boys had to resort to in order to make the CIS
> idea work more or less properly.  If you are worried about it,
> there are plugs available from Audi to close the holes in the
> air box and the intake duct after you rip the junk out. Look
> closely at the microfiche. No change in starting or running
> performance,. Just one less source of unmetered air and a lifetime
> of guilt from emitting the occasional puff of unburned hydrocarbons.
> I don't know if I can continue to live with myself.
> 
> DeWitt Harrison
> Boulder, CO
> 88 5kcstq