Lean condition under light acceleration

zakimodo said

Hi All
I am having this issue with a Thermoquad but assume that the method for addressing it is similar for any carb using metering rods. I have done some searching (maybe just not hitting the right keywords) and have not seen much on this topic. If there is a thread I have missed, please point me to it.

The lean condition is encountered under light acceleration or while engine load increases at constant throttle (climbing a hill).I have a wideband in the car which is aiding in tunning the carb. In addition to the gauge indicating a lean condition (16 to 17 AFR), I can feel it in the car as well.

Currently, the AFR is good while at cruise (13.7- 14.5, I could probably richen this up a bit) or under WOT (high 12's at the moment). I also have the secondary transition pretty much dialed in.

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It should get leaner with more throttle.
WHAT!
Yup.
Don't feel bad.
You, me, and most every hot rodder and wanna be hot rodder get the idea that the mix should get richer with more throttle.
It's only partially true. At idle (warmed up) engines generally want a somewhat rich mixture. And at wide open throttle with full load, engines require a somewhat rich mixture.
In between engines run best when provided leaner and leaner mixtures.
'Best' here being defined as engine running most efficiently in terms of torque and power.

If your Thermosquad is from a factory application fuel mixes at idle were targeted for leaner AFR's than would be used be used for most mechanical efficiency. The first targets in pollution reduction was idle and decelleration. Running leaner idle required slightly higher idle speeds and loss of fuel efficiency in return for big reductions in CO and leftover Hydrocarbons. Leaner again being relative. Idle ratios of 14 to 14.2 were leaner than non-emissions tunes which typically were in the 13:1 range.