Poor gas milage

I recently did a 140 mile round trip (90% freeway) and only got just shy of 21 mpg.
I kept it at around 65-70 mph, RPM's were around 3k if I remember right.
Just judging by the way the gas gauge is going down, in town MPG is worse.

History:
Truck has 157K miles on it, 2.0 B2000.
New head. New not rebuilt, with new valves, springs, but re-used cam.
It had a remanufactured stock carb on it when I got it. Looks like the mixture screws are uncovered (no plugs).
New NGK spark plugs.
Wires good.
Looks like it has a new O2 sensor.
Timing set correctly.
Compression not checked, but truck runs great, doesn't smoke, starts right up with no problems.

Things I'm not sure of:
When I installed the head, and set the adjustable rockers, I set them at .012, and rechecked/reset them after a heat cycle, as well as re-torqing the head. Not real experianced with adjustable rockers. .012 was snug, and had to force it to get a .013 shim in.

Questions:
What is the proccess for setting the carb mixture screws?
Can all the emission equiptment be causing the poor milage?
Can I remove the emissions equiptment with a stock carb by plugging and blocking off everything I remove?
Would I see an improvement by removing the catalytic convertors?

Lastly, but not likely due to funds, would I see a noticeable improvement by installing a weber?

Any other clues on where to start looking?

Mine started getting that way when the computer controlled jets started sticking. :/
I didn't wanna pay out the kind of money they wanted for a refurbished OEM carb or for the Weber kits, so I found rebuilt Holley 5200 (licensed weber copy of a weber 32/36 from the 70's) at and then got the adapter/gasket set off of ebay. So for about $150 including shipping I was able to get converted over.

Only thing different is the top of the carb, its a squashed oval shape as opposed to the weber 32/36 retangular shape. So I had to get a piece of metal and jig saw a bottom for the standard weber air cleaner. Also to make it easier to get new air cleaners in town here, I since then have manufacured a new top and bottom and am using a air filter from a dodge shadow.

I requested the carb for a 2.0L application, the jetting was right on, however I ordered some weber jets to rejet it a little leaner,

Only thing you gotta figure out when you order from him is which way you want it facing and want the throttle shaft to rotate.

I was trying to keep cost down so I didn't swap out the water choke for an electric, but since there are those two water hoses on the block under the manifold I just t'd in to those.

As far as a couple of the questions.. I emissions equipment can be causing poor mileage if not functioning properly. I noticed an improvement in both gas mileage and performance when I removed my cats, most of that probably was because they were pretty much plugged up solid, especially one on the manifold.

As far as removing the emissions equipment and keeping the stock carb, that is what I did for a bit after I installed my header. Though at this point my feedback jets were already sticking and fouled, which probably had alot to do with the fact that from when my uncle installed the take out motor in 93' until I put the Holley on about 4 years ago, that he had hooked up the fuel lines wrong, so that the fuel pump was feeding the carb through the unfiltered return line and pumping back through the filtered line. DOH!

As far as carb mixture screws on a stock carb *shrugs*

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Have a multi meter with the following funtions:
AC
DC
Continuity
K ohms
and diode check.

wish i could tell ya but honestly never got to drive mine far enough to see what the mpg was.
i know that i removed emmisions and cats. and got a header and glasspack. well yeah i dont like stock
soo.. i was running a stock carb and it seemed to run good. wether or not it has good or bad mileage i couldnt say.

oh yeah brett i just saw you rollin down portland rd wensday or was it yesterday. wait it was tusday. heck i dont know .. i know i saw you those. i was pointin at ya but you did see me. btw: truck is lookin real nice

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come on guys. some has to have more info for brett here..

I'll see what I can round up for one with a dwell setting this week and get back to you MazdaTweaker

Now have dwell meter for tests.
PM sent.