Rebuilt engine - 15 MPG! What can be wrong?

#1
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I live in a 3rd world country and the mechanics are not very trustworthy. I've spent so much money already, more than my '95 model is worth. My biggest problem right now is that I am getting less than 15 MPG on average. The car has approximately 600 miles on a rebuilt engine, I had new oversized (.030) pistons and rings, gaskets, etc. The cylinders were honed and the fuel injectors cleaned. I am not running with a catalytic converter (bypassed). I am wondering if those two hoses in the picture need to be plugged into something important. Please help me, 15 MPG is totally ridiculous for a small car.
 
#2
I do suspect that the two hoses in the photo may have something to do with my poor gas mileage but let me add some more details:

New spark plugs & wires, new air filter. New thermostat, and new radiator temperature sensor. Sometimes when the car is cold, you step on the gas and it does not move forward until I pump it and get the engine revved up. The mechanics are totally clueless and I can only think of the hoses in the image. Mechanics do not know where those plug into.
 
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