My '76 242 DL
is getting around 10-15MPG.
This really sucks, I've got a K&N air filter, new plugs and wires, new dizzy cap and rotor, new fuel filter, new oil and filter, new flame trap, cleaned my fuel tank, replaced a few fuel lines...blahblahblah

I recently blocked off my charcoal canister. The thing is rediculous and I felt unnecessary so I blocked all the lines and removed it. I doubt that's the problem, honestly.
Right now my timing is set at 10* BTDC at 900RPMs.

Any ideas?

I think there's a fuel leak, who knows where. How do I spot one?

 

It's eay to tell if you have a fuel leak just smell under the car after you park it. If you smell strong gas then you have a leak. If not you're good. Replacing the O2 sensor will get your millage up. also clean the throttle body.What kind of gas are you burning? If you live in a place where you can only get gasohol (the crap that is 10% ethanol) that decreases your millage but not by that much. Check your tires to make sure they are inflated properly and maybe add 2-3 pounds to increase millage. An oil change never hurts millage but it won't make a significant increase.