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]

My mustang goes super lean on throttle lift, as it should. My djet does not and often does as you describe and never goes super lean on lift. I wonder how many others have observed this.

[Van B]

I haven’t measured my AFR to compare so, I can’t say how mine does.

Do you ever get idle hang on deceleration i.e. it gets stuck above idle when you’re slowing down?

[Brian Fuerbach]

I haven’t measured my AFR to compare so, I can’t say how mine does.

Do you ever get idle hang on deceleration i.e. it gets stuck above idle when you’re slowing down?

I did have that problem in the past. One thing that helped was to adjust the decel regulator to bring the rpms down quickly to 1000 without going below. Of course this changes with engine temp so it was a balance. I switched to the 123 distributor and my transition to idle became nearly perfect. Idle is really steady now.

[Van B]

Ok so, two thoughts:

1.) set your decel valve to begin opening at 20 in-hg of vacuum.

2.) Does your 123 retain it’s advance on decel? I might be wrong here but I think the OEM dual vac pulls timing on decel

[Brian Fuerbach]

Ok so, two thoughts:

1.) set your decel valve to begin opening at 20 in-hg of vacuum.

2.) Does your 123 retain it’s advance on decel? I might be wrong here but I think the OEM dual vac pulls timing on decel

Good question. I have the vac capable 123 and I will have to check for sure if pulls the vac advance out on decel. I think it can be mapped to do both adv and retard but not sure. We are expecting some rain tomorrow so I will report my findings mid week. Maybe someone reading this can confirm if adv is active during decel.

[Van B]

Ok, I’m too tired to think straight but yes, your timing should retard when the throttle is closed regardless of RPM.

Timing retard vacuum is pulled from the bypass port on the throttle body, which is only used when the throttle plate is closed.

Look at line B

[wonkipop]

Ok, I’m too tired to think straight but yes, your timing should retard when the throttle is closed regardless of RPM.

Timing retard vacuum is pulled from the bypass port on the throttle body, which is only used when the throttle plate is closed.

Look at line B

you are not getting tired, you are getting really good.

correct on all counts.

why it would be rich....?
could be connected to that?
but i would have to think about that too.

those two ports behave slightly differently.

when throttle is fully closed the one on the manifold side of throttle plate activates retard can on distributor.

the other one, on the inlet side works at part throttle and cruise to advance the distributor.

and in typical VW fashion the advance one serves to cushion the distributors response to load.

but, its meant to lean for emissions when you close off throttle.

i'm just trying to remember how it goes.
might have to go back and re read manual to remind myself.
or alternatively clay perrine can just come in and say it in 5 words or less.

but i know the fuel pressure regulator does a bit at that point too.
backs off the fuel pressure - because its linked by vacuum to the plenum as well.
there is that t connection to the same vac line as the decel valve.
and there is something else that goes on with L jet probably in the afm.

get back to you if someone smarter doesn't do it first.

------

those double can distributors are amazing.
there are f$ck all cars in aus with them.
they belong to a period in time and USA cars in particular.
i have only really got my head into them since getting mine going again.
basically its the main emissions device? sort of.
we still had just advance can distributors on VWs here from same period in time.

-------
but in a carb car we wouldn't be worried if it was going full rich on throttle off deacceleration.
we only expect it to be lean because of emissions regs and fuel injection artificial intelligence combined with cuckoo clock mechanical devices aiding it.

???

or am i wrong.
but if its behaving properly as per EPA and being L jet, yeah it should go lean.

[emerygt350]

But here he is running a 123 right? so you have to choose retard or advance. My rich on lift didn't change when I switched from retard to advance (and moved the vacuum line appropriately).

I suspect with the butterfly closed, the pcv closed (on my 73, others may not have that), that the decel valve really can't let enough air in at meaningful rpms to thin the mix much. On a 1.8 I bet the vacuum operated fuel regulator (it is vacuum on the 1.8 right?) is a critical part of the lean on lift. Wonder if you have some issue there?

[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.

[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...

[ClayPerrine]

The AFM in an L-Jet system will push fuel into the ports as long as there is airflow through it. So on decel, you will have a lot of air moving through the AFM even if the flap is closed due to the engine spinning fast.

That may be causing the rich mixture you are seeing.

Clay

[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.

[emerygt350]

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...

I believe he said he was using a 123, so just one port on the dizzy.

[Van B]

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.

Everything is measured. Remember my first thread?

http://www.914world.com/bbs2/index.php?s=&...t&p=2958074

[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...

I believe he said he was using a 123, so just one port on the dizzy.

Right. Which is why I went with pertronix instead.

[emerygt350]

Is this correct?
I know they changed stuff every month on these things.

[Van B]

the little subset square on the airbox is meant to represent the AFM... poorly lol