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]

AFM is literally the barn door. it attaches to the air filter box and precedes everything. However, the car he's running here has two vac ports for the distributor. one for retarding and one for advancing. That's what I was showing on the page I posted. what that means is that there is progressive vac advance or no advance + vac retard and no retard.

Honestly, though, I have no clue what AFR should be expected from an L-jet at elevated RPM with a closed throttle. Without this ref we're just theorizing and having conversation for the sake of conversation lol...

[wonkipop]

AFM is literally the barn door. it attaches to the air filter box and precedes everything. However, the car he's running here has two vac ports for the distributor. one for retarding and one for advancing. That's what I was showing on the page I posted. what that means is that there is progressive vac advance or no advance + vac retard and no retard.

Honestly, though, I have no clue what AFR should be expected from an L-jet at elevated RPM with a closed throttle. Without this ref we're just theorizing and having conversation for the sake of conversation lol...

the throttle switch on the 1.8 operates at two positions.
idle. throttle closed.
wide open. (a position wonki occasionally enjoys torturing it with).

in between the flap in the afm does the fuel measurement (reacting to air amount).

i guess therefor fuel is metered by throttle body switch for the two extreme points.
when you snap the throttle closed the afm may be getting pulled open via the decel valve, but the fuel mix will be dictated by the throttle switch? ????

think i have that right. but happy to be corrected and unlearn something.

i'd have to think more about it precisely.
and go back and read some of the tech manuals.

i don't have a decel valve operational in mine.
and i haven't measured a/f mix on throttle closed, to know what it does.
but i suspect i don't have a rich air fuel mix on throttle closing as i don't get backfires.
ie not dumping fuel rich mix into a hot exhaust where it can detonate.
but i suppose it could still be rich, just not rich enough to backfire.

the decel is supposed to stop the engine going below idle, dying and coming back to life.
that can happen with my car, but only when still cold.
a weird thing where you snap closed the throttle and then there is a second of silence before normal service resumes.


so....the rich thing is interesting.

i don't know how fast the dist would return to full retard idle position.
its in its centrifigal phase as revs come down.
the vac can would have very little advance action going on from the port in front of the throttle blade. it would be in full retard action if hooked up properly to the retard port on the tb or to a vacuum source in the plenum. which means all the way down as revs decline the dist will be that 3-4 degrees further retarded than if it were a pure centrifigal dist. and that would be making the burn more complete. which is what the emissions oriented design is meant to do.