You need to unplug that passage. The choke is sticking on if it is operable at all and you are coking up the engine if it's plugged. You are losing 5-10MPG if it's plugged and gumming up the engine as well.

Sheldon

Maybe my issue isn't so much with the crossover as you all seem to think. In Nitrousn's explanation, he commented about the choke operation as did Runcharger and his comment about if the choke is even operational. Well, the choke is fully operational and when the engine warms up the choke fully opens. I'm not saying that the passage might not be plugged as suggested. I'm just saying that maybe this isn't the absolute cure for my problem.

I would also point out that not too long ago another member posted about a hesitation/bog with his 318 equipped with the same Holley 2280 2bbl I have and no one told him his passage was plugged. Turns out his problem was the power piston and I had asked for more specifics but never got an answer. EVERY 318 I've ever owned, either with the Carter BBD or this Holley has always has this same bog. I've just learned to drive with it. I know my main question with this thread was about increasing fuel mileage, but in this case I think the two may be related. If my power piston was stuck in an enriched position, could it cause the hesitation and also allow it to run rich at cruise, reducing mileage? Also, I don't think the mileage with this truck is too far off average. I'd say about 10 or so around town and about 14 on the highway. I was just looking for a way to improve on that if possible.

If you really want to chase the best mileage you can get, I would highly recommend finding a wideband O2 sensor.

Without knowing exactly what's going on AFR-wise, every modification is a SWAG.

My last 87 4x4 318 auto would do 17 mpg highway all day long and 14 city. My 84 2wd 318 would do 20 hwy and 15 city. So you are easily 4 to 6 from what it will get. 50 bucks in parts and a good 4 to 6 hours could get you where you would like to be. What other mod can you do for so cheap??? One tank of fuel the savings would pay for the parts. I am done with this post.

I bought a new 86, 318, D150 and it got 17-18 MPG dead stock with 3.21's so that's what you can shoot for with it totally stock.
BTW, I have never swapped a 2 bbl to a 4 bbl and gained mileage ever. I've tried it on 318's, 360's, 383's, 400's and they always got worse, TQ, AFB, AVS, Holley it didn't matter and I am a much above average carb. tuner.
Stock 2 bbl, dual exhaust (headers too) and an optimized advance curve along with tight ring seal and good timing set are key elements to fuel economy mechanical wise IMO.

Sheldon