Afr reading

[Garrick Clark]

Hi. I'm using a pair of 40 dells on my N/A engine.
When I drive it at a constant speed, say 60, 1/3 rd throttle opening I'm at 13.1. Then when I lift off the throttle the gauge shows 10.

Sussed it. On over run , throttle is closed ,so vac pulls fuel out the mixture screws and no AIR will enter the engine  because of closed throttle plates resulting in a rich mixture which shows me 10 on the gauge.

[Martin S.]

Interesting. That’s likely why my fuel injection system has a deceleration cut off.
It can feel like an electric brake on a circular saw