I've got my Holley 600 CFM Vac secondary carb pretty much dialed in with a Wide Band O2 sensor. Idle is around 13.9 to 14.5, cruise is 14.1-15.2 and WOT is around 13.

When cruising around if I let my foot off the gas the gauge immediately shows lean. Is this normal? I have a manual transmission and If I engine brake by letting off the gas at anything over 2500 rpm, the effect is more pronounced.

In fact, anything over 3500 rpm and letting off the gas, the gauge shows max lean and goes past it's limit.

Everything is back to normal the second my foot is back on the gas or I push the clutch in letting the engine drop to idle.

Is this normal behavior for a carb on a manual transmission car? I know going lean is not good for the motor.

 

Lean on decel like that isnt goin to hurt anything, it just makes it engine brake harder if you lean it out and giving it alot of timing in those areas. If you wanted to coast on more on decel, it needs to be richer.

EFI cars do it all the time. Decel Enleanment. Helps save fuel and basically pumps air thru the motor and that helps cool things down on deceleration.

 

Ok thanks that's good to know. I do get a pop or bark every now and then while decelerating from high rpms in gear. My Yamaha V-twin motorcycle did that a lot.

 

yeah its probably backfiring out the exhaust due to fresh air and unburnt fuel getting ignited in the exhaust. An exhaust leak will do this, as it will pull fresh air in from high vacuum deceleration, and cause some unburnt fuel in the exhaust to ignite.