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]

Definitely possible.
As you've seen through my quests, the air from the decel valve is still measured air since it pulls from the intake boot after the AFM barn door. If the decel valve is flowing air when it shouldn't be, then the AFM will fuel the engine. I'm thinking maybe it could be too much fuel given the throttle body is fully closed in those moments.
In my view, you only want the decel valve to open at moments of high vac... throttle chops etc.

My point about timing is that if it remains advanced when the throttle is closed, then the burn won't be right and will almost certainly show a low AFR (rich)

[Van B]

Definitely possible.
As you've seen through my quests, the air from the decel valve is still measured air since it pulls from the intake boot after the AFM barn door. If the decel valve is flowing air when it shouldn't be, then the AFM will fuel the engine. I'm thinking maybe it could be too much fuel given the throttle body is fully closed in those moments.
In my view, you only want the decel valve to open at moments of high vac... throttle chops etc.

My point about timing is that if it remains advanced when the throttle is closed, then the burn won't be right and will almost certainly show a low AFR (rich)

Now that I think about what I just posted, I bet there is more than one cause/tuning issue at play here.

[emerygt350]

Definitely possible.
As you've seen through my quests, the air from the decel valve is still measured air since it pulls from the intake boot after the AFM barn door. If the decel valve is flowing air when it shouldn't be, then the AFM will fuel the engine. I'm thinking maybe it could be too much fuel given the throttle body is fully closed in those moments.
In my view, you only want the decel valve to open at moments of high vac... throttle chops etc.

My point about timing is that if it remains advanced when the throttle is closed, then the burn won't be right and will almost certainly show a low AFR (rich)

Now that I think about what I just posted, I bet there is more than one cause/tuning issue at play here.

Is the AFM before or after the boot? I need to put up a diagram of these two systems. Advance should pull out as long as you have it attached to ported vacuum. Perhaps that might be an issue here? If the vacuum advance is hooked to the plenum you would end up with advance when you lift rather than during slight throttle opening.