L-Jet going full Rich on Deceleration Options

[Brian Fuerbach]

1974 1.8 with L- jet. Been playing with a wide band air fuel meter and noticed that when I lift the throttle the AFR goes to max value on the gauge. I thought it was supposed to go lean. I checked the throttle position switch and it checks out fine. Going to check the wiring harness next.

What else should I check? Decel valve?

[Van B]

Ok, I’m too tired to think straight but yes, your timing should retard when the throttle is closed regardless of RPM.

Timing retard vacuum is pulled from the bypass port on the throttle body, which is only used when the throttle plate is closed.

Look at line B

[wonkipop]

Ok, I’m too tired to think straight but yes, your timing should retard when the throttle is closed regardless of RPM.

Timing retard vacuum is pulled from the bypass port on the throttle body, which is only used when the throttle plate is closed.

Look at line B

you are not getting tired, you are getting really good.

correct on all counts.

why it would be rich....?
could be connected to that?
but i would have to think about that too.

those two ports behave slightly differently.

when throttle is fully closed the one on the manifold side of throttle plate activates retard can on distributor.

the other one, on the inlet side works at part throttle and cruise to advance the distributor.

and in typical VW fashion the advance one serves to cushion the distributors response to load.

but, its meant to lean for emissions when you close off throttle.

i'm just trying to remember how it goes.
might have to go back and re read manual to remind myself.
or alternatively clay perrine can just come in and say it in 5 words or less.

but i know the fuel pressure regulator does a bit at that point too.
backs off the fuel pressure - because its linked by vacuum to the plenum as well.
there is that t connection to the same vac line as the decel valve.
and there is something else that goes on with L jet probably in the afm.

get back to you if someone smarter doesn't do it first.

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those double can distributors are amazing.
there are f$ck all cars in aus with them.
they belong to a period in time and USA cars in particular.
i have only really got my head into them since getting mine going again.
basically its the main emissions device? sort of.
we still had just advance can distributors on VWs here from same period in time.

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but in a carb car we wouldn't be worried if it was going full rich on throttle off deacceleration.
we only expect it to be lean because of emissions regs and fuel injection artificial intelligence combined with cuckoo clock mechanical devices aiding it.

???

or am i wrong.
but if its behaving properly as per EPA and being L jet, yeah it should go lean.

[emerygt350]

But here he is running a 123 right? so you have to choose retard or advance. My rich on lift didn't change when I switched from retard to advance (and moved the vacuum line appropriately).

I suspect with the butterfly closed, the pcv closed (on my 73, others may not have that), that the decel valve really can't let enough air in at meaningful rpms to thin the mix much. On a 1.8 I bet the vacuum operated fuel regulator (it is vacuum on the 1.8 right?) is a critical part of the lean on lift. Wonder if you have some issue there?