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]

Your vac readings are what my decel valve yielded when my car was giving me high idle problems after deceleration. I turned the screw in until I got 20” and 23”.

Regardless, your numbers seem ok. Maybe it’s somewhat of a contributing cause, since we’re talking about a tuning issue and not a fault?


Throttle switch checks out. It doesn’t do anything between idle and WOT on an L-Jet. So, most importantly it does know that your throttle is closed. If it didn’t, I think you would have other issues.

Maybe that table I posted can help you improve your tune on the 123 distributor? Knowing vac levels for when the timing should retard or advance, and by how many additional degrees, as well as centrifugal data for the OE distributor would allow you to better mimic OE.

If that is all set up, I’d say the AFR you get is what it is and nothing to worry about.

[wonkipop]

Your vac readings are what my decel valve yielded when my car was giving me high idle problems after deceleration. I turned the screw in until I got 20” and 23”.

Regardless, your numbers seem ok. Maybe it’s somewhat of a contributing cause, since we’re talking about a tuning issue and not a fault?


Throttle switch checks out. It doesn’t do anything between idle and WOT on an L-Jet. So, most importantly it does know that your throttle is closed. If it didn’t, I think you would have other issues.

Maybe that table I posted can help you improve your tune on the 123 distributor? Knowing vac levels for when the timing should retard or advance, and by how many additional degrees, as well as centrifugal data for the OE distributor would allow you to better mimic OE.

If that is all set up, I’d say the AFR you get is what it is and nothing to worry about.

yes, that is how i read it. the ECU knows when the throttle is closed.
the rest of the time its hand off to AFM. but even at idle the flapper is moved.
? still it seems to want to know the throttle is closed.

although its not clear to me if it does another thing at full wide open.
or it just assumes if its not idle, then after that its open or on the way to wide open and lets the AFM do its job.

the test done by Brian says his throttle switch is fine.

part throttle decelerating might be another thing?
where you don't close the throttle off but only come down partly off revs rather than a hard release of the gas pedal. but just the same the flapper moves and electrons travel faster than air to the valve so the ECU is way in front of the O2 by the time it gets there, and its giving the right amount of fuel.

got to be all hard wired to the original expectations around the distributor and timing?

one thing i do know is those california EC-As in 74 just operated the distributor in retard mode only. so even when you were cruising they were forcing the engine to be retarded (slightly retarding the centrifigal position) and run "cleaner" on certain emissions. whereas the EC-Bs in 74 at least let you do advance at cruise and get fuel economy. and that was all just done off the distributor and pretty much nothing else. as far as i can figure out the california retard only distributor was a bit of blunt instrument that took a nice sophisticated instrument like a double can distributor and turned it against itself?

which might point to the 123 and just how the advance and retard work.