1986 B2000 Gas Mileage?
 

Hello everyone,
Had a couple questions about my truck, so I decided I would sign up for some help :D

I have a 1986 B2000 5Speed 2x4. When the vehicle is cold (not weather wise, but the literal engine), it smokes black smoke for a couple seconds, then smokes a ton of blue smoke. I imagine the blue smoke is from bad valve seals, but what would the black smoke mean? I've only seen black smoke from a diesel...

Also, I filled it up today and calculated the gas mileage. It only got 14.2 MPG. What would be causing this?

The ODO shows 296,xxx miles, but the engine was either rebuilt or replaced, and has around 100k or so to my knowledge.

It never has trouble staying running or dying, the only major thing would be sputtering when the engine is cold and having to hold the gas down until it stops. If needed, I suppose I could take a video of the smoke and rough running. Here is a previous video if it makes a difference.

Well, the black smoke is rich mixture (unburnt fuel). Could be a lot of things causing it to run rich. O2 (oxygen) sensor bad is common. Choke not fully opening or other carb problems, EGR not closing, to name a few.

The engine light would come on if it was the o2 or the EGR though, wouldnt it? Last mileage I got was 11.7 MPG. I used some carb cleaner, which made the truck backfire and have black smoke pour out the exhaust. Best guess is carb problems. Is there a way to adjust it somehow to somewhat correct the issue? Or would it call for a new carb?