Stupid metering plate questions in a CIS (probably also CIS-E) VW:
1) If I take the top of the airfilter box out and turn it upside down,
should the metering plate just open by gravity? After all, when in the car
gravity will bring it down.
2) Does it have some kind of damping in its hinge, to account for bumpy
roads and so on?
3) This one is the hardest: how sluggish should it feel? Say, you turn it
sideways and move it with you hand. How should it feel?
(if you need to email me, use this address =)
email@example.com (Mauricio) wrote in message
The metering plate has a counterbalancing weight on the opposite end
of the lever, beyond the pivot. In theory it will be perfectly
balanced. In practice, if you turn the fuel distributor upsided down,
the metering plate might fall slowly open by gravity (indicating
things are slightly out of balance).
If the fuel system is pressurized and you turn the fuel
distributor/air flow meter upside down, the metering plate should
probably not fall open. The fuel pressure on the plunger should keep
the metering plate closed.
There is no damping. There is a counterbalance weight. When you run
over bumps, both the counterbalance weight and the metering plate have
equal forces acting on them, and the whole thing remains balanced.
The only thing that might mess up the mixture slightly is if the car
rotates along the axis of the pivot. The inertia of the metering plate
and the counterbalance can cause the arm to move and can change the
fuel delivery rate slightly (actually, the arm, metering plate and
counterbalance weight stay static and the housing moves, but the
effect is the same).
Generally speaking, if you start to rotate the car quickly on that
axis, or have the car rotating on that axis and quickly stop the
rotation, you have far more serious problems than the fuel mixture
With pressure in the fuel system, there should be some resistance to
lifting the plate. It should be smooth throughout it's operating
range. Also, if you lift the plate and then drop it suddenly, the
piston probably won't fall as quickly as the metering plate. If you
lift it immediately after dropping it quickly, there will be no
resistance for part of the way up, until you reach the point where the
plunger is, then you will feel the slight resistance again. It takes
about a second (rough guess) for the plunger to return from the top to
1984 VW Jetta Diesel GT
1992 Mazda Miata
1994 Caravan (OK, maybe it's a keeper, but I still want a VW Caddy)
1983 VW Rabbit GTI (ITB racer)
1981 VW Jetta (planned to be monster turbo project)
1988 Mazda RX-7 (Soon to be ITS racer)
1992 GMC Topkick (portable garage for racecar[s])
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