Strange Weber 32/36 DGAV behavior

[JFENG]

I was at a friends house to see how his nut and bolt E9 was running. He has older emission style Weber 32/36’s with
Water chokes and idle cutoff solenoidsz first thing I did was to put the lead on each solenoid to confirm the engine would then run like crap. Both solenoids seemed to be working but with a noticeable lag.

We let it warm up and the idle settled at about 800. I put my AFM in the tailpipe to see where he was on idle mixture.

Here is the strange part: idle was a solid/steady 22.4:1. ULTRA lean. I turned the idle screws three full turns from the “too lean” point and I still couldn't get the system to go richer than about 21:1

As soon as he put the car into drive (slushbox) the AFM dropped to 15-16.

FWIW, The engine reved up nicely with no sign of a super lean condition. Car drove fine too with no hesitation or flat spots. i didn’t have time to remove his adaptor plates and record his jetting.

any idea why
(1) the idle mixture is that lean
(2) the idle mixture doesn’t respond to three full turns on the moxture screws. Are the emission carbs that insensitive to screw adjustment t?

 

[Stevehose]

Sounds like the afm is getting air from the back of the pipe. I dont see how it can idle solid/steady at that lean number

 

[JFENG]

Sounds like the afm is getting air from the back of the pipe. I dont see how it can idle solid/steady at that lean number

That’s what I thought. So I increased the rpm to 1200 and still 22:1. Then we put it in gear with the brake depressed. Rpm when down, of course and the mixtures dropped to the 15-16:1 range.

anyway, I agree that we must have been getting fresh air contamination due to exhaust reversion.