O2 reading and help jetting

[advinnie]

Hi all. I have a 1600 Vw beetle that is running a AMR 500 supercharger in a draw through set up using a Weber 40 DCOE carburettor. I am only running 5 psi boost on this set up and it starts and drives fine but it could be better and it is running rich.

I have an O2 sensor plugged in on a vintage speed twin pipe exhaust and I’m getting a rich reading but would you say it the idles or mains ?

At idle the O2 gauge is displaying 12.65
At any steady through position in any gear at any rpm from idle to 3000rpm the gauge is displaying 10.00 which is it max richness reading.
Will this be an idle yet change?

Now when on boost of 5psi from 1000 rpm to 3000 rpm the gauge reads 11.64 to 12.01. Then from 3000 rom to 4500 rpm the reads 12.5 to 12.6.

So I’m guess that when on boost the mains are working and when on steady throttle it’s just the idle jets ?

Last question is what should the air/fuel ratio be when on cruise and when on boost.

Thanks all

[panel]

Do you have a wideband or narrow band set up ?

[advinnie]

It’s a wide band

[Piledriver]

Idle fuel and idle air as well as the idle screws control cruise
mains and their air jets are wot.
Your mains sound good, air corrections might need to go smaller, as you are starting to lean out at higher rpm.
11-12:1 is a good target range for boost.

You need to get smaller idle fuels at least.

In the old days, you could roughly judge if the fuel jet as too big or too small by how far the screw was in at idle, the "ideal" setting was around 1-1/2 turns out from closed, although the wideband/cruise mix should take priority, and the idle screw setting should end up where needed.

https://www.redlineweber.com/html/Tech/ ... best_.html

The transition is likely to be rough tipping into the throttle as fuel tends to pool in draw through setups, but it should cruise and do WOT fine once you sort the jetting.

Confession:
I'm in the EFI camp, Love the look of a drawthrough but would probably put injectors in at the intake ports and use the weber as a throttle body.(if I wanted old school look) Cant run an intercooler that way but you could run water injection. That way you could really control the fuel (and programmable ignition) and have excellent driveability.

[advinnie]

Hi all. I have reduced my idle jets now to 40f9 and I have a much better air fuel ratio at idle of 13.8:1 and the mixture screws are 1 1/2 turns out. The car feels much lighter and happy now which is good but I still peg my gauge at 10:1 when at light throttle/cruising but now it will flicker between 10:1 to 10.5:1. The second I take my foot off the accelerator the engine leans up to 13:1. Is this still an indication that the idles are still to rich ?
Or is this something I will just have to live with running supercharger in a draw through set up?

[Piledriver]

You can try larger idle airs, but I'd probably try one size smaller on idle fuel first.
Should shoot for 15-16:1 ish at light cruise, as long as you have vacuum advance, lean mix burns slow, requires far more timing..
If you lack vacuum advance, you should consider fixing that, the factory dual vac cans also allow boost retard.

[slayer61]

https://web.archive.org/web/20230617225 ... -4-engine/

Thanks to John Connolly, a tutorial about using the afr gauge while tuning an air cooled vw motor.

[advinnie]

Thank you for that information

[advinnie]

Hi all. So after reading that link that was posted up I figured something out but not to sure on what to do.
So with no main jet stack fitted and running 45f8 idles I have an idle A/F ratio of 13.7:1 with the mixture screws turned out 1 1/2 turns. Now with the main stacks out go for a drive and I have a lovely cruise ratio of 15.2:1 up to around 2300 ish rpm, around this rpm I hit a lean hole due to no main jet stacks fitted. Now fitted the main jet stack and any cruise/ light throttle over 1200 rpm I go super rich at 10:1. Now the floats are set to 8.5mm, the progression ports or not uncovered at idle. The mains are coming on way way too early. I’ve tried swapping out my F2 emulsions with F11’s but all that did was lean out my acceleration A/F ratios. I’m using 200 air correction jets at the moment so I may increase these to 210 or 220 to delay the mains coming in. Has anyone got any over ideas I can try?

I thinking that the supercharger is causing so much vacuum that it’s effecting when the mains come in

[slayer61]

I'm glad you made some headway on your idle jetting. A 40 F9 sure seemed like a weird size.... a lean number on the fuel side, and a rich air side!??

[advinnie]

H all. I’m looking at going EFI on you super charger but don’t know where to start. Any help would be great on how to go to EFI

[panel]

Have you picked a brand of EFI yet ?

[advinnie]

No not yet. I’m at the very first stage or figuring out what I need.

[Bruce.m]

Big topic. Lots to learn & research, unless you are happy to hand over to someone & pay the bill.