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]

Distributor vacuum is read/pulled from the throttle body not the manifold. So, that will be a different level of vacuum than in the actual manifold. And, the placement of the ports provides further difference.

Generally speaking, what the distributor sees at a closed throttle is no different at idle or any RPM when the throttle is closed.

Per the manual, there is a max of 32 degrees centrifugal advance and a max of 12 degrees vacuum advance. But, any time the throttle is closed the advance port is blocked, so that advance is immediately dropped AND retard is fully applied.

Thus, what remains is your centrifugal curve.
And again, per the manual, it would wind down from a max of 32 degrees at or above 3200RPM to 23.5-26.5 at or below 2500RPM, and finally 14.5-19 degrees between 1180 and 1500 RPM.
And since the throttle is closed, you would subtract the amount of applied retard to all of the above figures.

If the 123ignition distributor is not mimicking that profile then all bets are off for AFRs on closed throttle. The AFR is not measuring fuel nor air, it is only measuring effective combustion.

[wonkipop]

Distributor vacuum is read/pulled from the throttle body not the manifold. So, that will be a different level of vacuum than in the actual manifold. And, the placement of the ports provides further difference.

Generally speaking, what the distributor sees at a closed throttle is no different at idle or any RPM when the throttle is closed.

Per the manual, there is a max of 32 degrees centrifugal advance and a max of 12 degrees vacuum advance. But, any time the throttle is closed the advance port is blocked, so that advance is immediately dropped AND retard is fully applied.

Thus, what remains is your centrifugal curve.
And again, per the manual, it would wind down from a max of 32 degrees at or above 3200RPM to 23.5-26.5 at or below 2500RPM, and finally 14.5-19 degrees between 1180 and 1500 RPM.
And since the throttle is closed, you would subtract the amount of applied retard to all of the above figures.

If the 123ignition distributor is not mimicking that profile then all bets are off for AFRs on closed throttle. The AFR is not measuring fuel nor air, it is only measuring effective combustion.

ok.
so i have the distributor bit right.
phew!

the afr measures oxygen to deduce effective combustion?

how does it do that - the effective combustion bit.
i've read a few things about 02 sensors but i don't quite get how they translate that into other information.

[Van B]

Distributor vacuum is read/pulled from the throttle body not the manifold. So, that will be a different level of vacuum than in the actual manifold. And, the placement of the ports provides further difference.

Generally speaking, what the distributor sees at a closed throttle is no different at idle or any RPM when the throttle is closed.

Per the manual, there is a max of 32 degrees centrifugal advance and a max of 12 degrees vacuum advance. But, any time the throttle is closed the advance port is blocked, so that advance is immediately dropped AND retard is fully applied.

Thus, what remains is your centrifugal curve.
And again, per the manual, it would wind down from a max of 32 degrees at or above 3200RPM to 23.5-26.5 at or below 2500RPM, and finally 14.5-19 degrees between 1180 and 1500 RPM.
And since the throttle is closed, you would subtract the amount of applied retard to all of the above figures.

If the 123ignition distributor is not mimicking that profile then all bets are off for AFRs on closed throttle. The AFR is not measuring fuel nor air, it is only measuring effective combustion.

ok.
so i have the distributor bit right.
phew!

the afr measures oxygen to deduce effective combustion?

how does it do that - the effective combustion bit.
i've read a few things about 02 sensors but i don't quite get how they translate that into other information.

Charts like this are worth so much IMO.