i know this is a dumb question, but what does it mean to be running lean?

 

running lean means that your air/fuel ratio is too large.. the 'ideal' ratio, if im right, is 14/1 (14 to 1) meaning 14 parts air for every 1 part gas. some dyno's will measure the ratio as the engine increases in rpm's, and you can see, even on 'tuned' engines, it may drop to 9/1 at some points, which is quite rich, but may go all the way up to 17/1 at other rpms. i think it was in the pack of info i got with my edelbrock carb when i bought it that said when it gets down around 5/1, its at the extreme limit.. meaning it wont run if it gets any 'richer'. so, to answer your question, 'running lean' means that there is too much air in relation to the amount of gas that is going in your engine. you can measure this with an A/F(air/fuel) ratio tool, sold in Summit (www.summitracing.com), but is quite expensive at 130 bucks. just for your info, it is a sensor that detects the amount of oxygen in your exhaust(correct me if im wrong someone). clear it up for you?

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• 83 Z28--ttops, 200k miles--very ragged out. sold after a year of owning it
• 74 Z28--slightly modded 383, TH400 tranny, 10 bolt rear, not to swift, but a 700R4 and EFI is on the way

 

I believe that your correct cause some of them plug right into your oxygen sensor, so go figure....

 

That is in molecular or molar mass ratios, not volume ratios. It's not saying for every gallon of gasoline, you need 14 gallons of air. More like for every molecule or pound of gas, you need 14 air (20% O2)molecules or pounds. It's something along those lines anyway (It's been at least a year since I've taken Thermodynamics).