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?

[emerygt350]

So a decel hooked to the boot would be unmeasured air? AFM -> Boot -> throttle body? or is it Throttle body -> AFM -> Boot? If it is the first situation, the closed throttle body should reduce flow across the AFM and result in high plenum vacuum and the decel leading to the boot would cheat the AFM. I would think you would want the decel after the throttle body to be most effective and cheat the AFM.

[wonkipop]

So a decel hooked to the boot would be unmeasured air? AFM -> Boot -> throttle body? or is it Throttle body -> AFM -> Boot? If it is the first situation, the closed throttle body should reduce flow across the AFM and result in high plenum vacuum and the decel leading to the boot would cheat the AFM. I would think you would want the decel after the throttle body to be most effective and cheat the AFM.

no. not quite emery.

the decel valve is cheating the throttle body is all that is happening.
and its pulling the flapper open as a kind of second throttle body.

the decel gets pulled open by vacuum in the plenum when the throttle is closed.
this operates an alternative route for air which is (and can only be) drawn past the flapper - and therefor operating it.

vacuum declines as revs drop and the decel gradually closes.
closing the air route.

its basically just slowing down the action of closing the throttle so its not so violent, on and off. which is why a lot of the 911 guys used to rip the decel valves off.
i think in the case of the 911 guys it was on the K jetronic system? they hated them.
they wanted violent on off throttle. (something to do with having an engine in the wrong place in the car and going around corners?).

the decel valve is operated by the same vacuum line that branches off to the fuel pressure regulator. so on decel the same vacuum opens up the fuel pressure regulator a bit more and drops fuel pressure.

which is why i am still thinking. because fuel pressure and dropping fuel pressure does come into it with L jet. exactly how it affects things i can't really say. but L jet is wanting to drop the fuel pressure on throttle closing situations.