'71 Runs Better in Cool Weather/Wet, What Gives?

[Dan in Pasadena]

Posting for a friend- his PC is out of service.

His '71T has a pretty freshly rebuilt 2.2 with stock carbs. He notices the car seems to run much more powefully, and smoother too if it is a cool morning or a wet day. Is this imagination or is there something to it?

Need opinions from experienced early 911 guys.

[john walker's workshop]

cold DENSE air. more oxygen molecules packed into the fuel/air mix. the intercooler principal.

[cactusdtd]

jw is dead on the money. no other explanation needed. density = air pressure / (R x temp) where R is a gas constant. bottom line......density is inversely related to temp. the lower the temp, the denser the air; the higher the temp, the less dense the air

[masraum]

cold should make more power, but I wouldn't think "wet" would unless it was because the "wet" mornings were also cool.

I would think that if he's noticing much more than just a little more power that something may not be quite right. Maybe he's running rich or something, and it runs better when it's getting denser air, but I defer to people like JW or Warren for that sort if stuff. I don't have enough carb experience other than the basics, and don't remember how my old cars were.

[Dan in Pasadena]

Thanks guys,

Yeah, it is basic science that cooler air equals more dense air and given a fixed amount of fuel the fuel/air ratio is changing. SInce his car is running better, apparently it is running too rich in "normal" temperature conditions.

So my question is what does he need to do? Is it just a matter of having an experienced carb man make the adjustments?

[randywebb]

wet mornings usually ar cooler -- the air has cooled all the way down to the dew point which it rarely goes below

also - wet air might act a bit like a water inj. system...

[john walker's workshop]

carbs generally run a tad rich anyway, nature of the beast. they're not as efficient (gas mileage-wise) as a fuel injection system. lean them out and you get bogging and hesitation. so his carbs may actually be fine.