Almost. but you have the functions of the systems mixed up a bit.
The Air pump (smog pump) should NEVER pump exaust gasses anywhere. It
pumps air through a pipe to the exaust manifold (there is a check valve
on the air manifold to prevent exaust gasses from coming in to the
system). Where the air is blown in to the hot exaust as it comes out of
the engine. The theory on this is if there is any un-burned fuel (seen as
hc on a "sniffer") with the introduction of the "new" air compleat with a
fresh supply of O2 will oxidize and burn the remaining fuel. (This is why
the exaust gets so hot on these engines and things crack over time)
The gulp valve is to supply extra air to the intake side, This is
only supposed to happen during periods of high manifold vacuum. ie.
decelerating. or engine breaking (ohh noo not again).During decel a lot
of fuel is drawn in to the engine but not enough air so the hc and co
readings go off the scales - and if the air pump is running all this
unburned fuel will explode in the exaust. That is the "backfire" you hear
when you shift or slow down.
There is another system called egr that does collect exaust gas
and "try" to reburn it, unsuccsfully. The theory here is to reduce
combustion temp & pressure, reducing NOx emisions.
The crankcase ventalation system is for the collection of blow by
gasses that get past the rings these are collected by the pcv valve and
the vent pipe and sent back to the intake side.
The last system efe (early fuel evaporative) system it collects
fuel vapors from the carb bowls, air cleaner, and gas tank. these fumes
are collected in a carbon canister for later use by the engine. This is
most often done during periods of cruise via a valve that opens a purge
line to the carbon canister. These fumes are then burnt in the usual
manor.
Hope this clears the air on the smog stuff. :)
LEX
> The emmisions system on the '71 MGB (US), and I think it is identical
> to the '72 MGB, goes as follows..
>
> Exhaust gasses are pumped out of the cylinder head via a copper header
> pipe attached to an air pump (belt driven off the cooling fan pulley).
> Gasses flow through the pump, mixed with outside air (comes through a
> small air filter) and sent to a "gulp" valve. The "gulp" valve has a very
> small vacuum line attached to the intake manifold (which actuates its
> opening and closing, I guess based on speed) and allows the pumped air to
> be gulped into the intake manifold via yet another line out of the gulp
> valve. Any additional gasses which are not burned, or which acumulate in
> the crankcase and do not come out of the head to the pump and re-burned
> as above, come out of a breather pipe attached to the left (forward)
> pushrod cover. The fumes from here are drawn into the carbeurators, an
> additional air line entering the top of the float bowls on each carb. and
> the third component... any fuel spilling or overflowing out of the float
> bowls, or gas fumes primarily I suspect, are sent via a "y" header pipe
> and a hose and metal tube to a charcoal absorption canister mounted above
> the passenger footwell, in the engine bulkhead. Another fume/fuel
> recovery line comes from the fuel tank area, there is a recovery canister
> attached to a vent hole in the fuel tank top and is secured to the rear
> right corner of the trunk (boot). This line also goes to the charcoal
> canister under the hood (bonnet). AND FINALLY, a recovery line, larger,
> goes from the charcoal cannister to the rocker cover, via a copper pipe
> with a very small hole mounted to the rear reight corner of the rocker
> cover. This allows these gasoline fumes to be drawn into the crankcase
> where they would come out through the previous system, via the PushRod
> cover vent to the carbs.... A closed but breathing system, actually as
> Scott Fisher put it, quite simple really...
>
> well, thus ends my '71 / '72 MGB emissions dissertation, partly c/o Scott
> Fisher #1....I will post this part for others....
>
> Correct me ya'll if I blew anything here....
>
> POSTED FOR REF TO OTHERS. "non-tech chat" deleted.
>
> CHEERS....
>
> Jim Fink
> '69 & '71 MGB's
>
>
>
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