[Mgs] Gulp valve: how would I know that it has failed?

[Simon Matthews]

Backfire can also occur when the mixture is too lean: if the mixture
becomes sufficiently lean, no ignition will take place in some cycles,
leading to fuel in the exhaust.

The car has been running  lean. I have compensated by adjusting the
mixture, but realized recently that there might be an intake leak.
Some time back, the car was running rich and I leaned it out. Now the
condition of the  spark plugs and the way it drives and responds to
the choke suggest that it is lean.

Some time back, I tested the area round the throttle shaft for leaks
and did not find anything, but had forgotten to look for other
possible leaks. Of course the 3-way connector for the crankcase vent
fell apart in my hand when I decided to look at that, so that port in
the intake manifold is plugged while I wait for a replacement part. I
also plugged the port for the control input to the gulp valve.

The other two possible causes are, I think, leaking vacuum advance
unit and the gulp valve.

Simon

On Tue, Dec 13, 2016 at 9:00 AM, PaulHunt73 <paulhunt73 at virginmedia.com> wrote:
> Backfiring occurs because when you shut the throttle on the overrun the
> mixture becomes rich.  Normally not much of a problem, but with the exhaust
> air injection the rich mixture (without a gulp valve) combusts in the
> exhaust.
>
> Certainly when open the gulp valve does inject air into the inlet.  Normally
> this is only when the throttle is closed i.e. high manifold vacuum.  If it
> were stuck open all the time I think you would know about it from very poor
> running, even if you had maladjusted the mixture in an attempt to compensate
> for it.
>
> Normally they stick closed, and cause backfiring.
>
> PaulH.
>
>
> ----- Original Message -----
>>
>> I was wondering if there is a failure mode in which the gulp valve
>> always allows air through, so making the engine run lean all the time.
>>
>