'94 ford ranger 4x4 4.0l v6, how to get better mpg

[cornhusker]

i have an oct. of '94 mazda b4000 4x4(ford ranger) it has a 4.0l v6 with a k&n drop in filter, the tires that came with it are 235/75/15 the door jam says it needs 265/75/15
right now im getting 12city and 15highway mpg
its suppose to get 18 and 23 or somthin like that
will the smaller tires cause it to get this bad of gas mileage?
my muffler is also leaking, does that make worse gas mileage?
what should i do?
thank you ahead of time for any info.

[MonteCarlo31]

Yes the smaller tires can cause poor gas mileage as can poor spark and fuel flow, change your plugs, wires, cap if you have one, and fuel filter. Keep us posted.

[cornhusker]

changed fuel filter, plugs, and wires. still getting bad gas mileage. will clogged cats give me bad gas mileage?

[nismokid]

Go buy the TORNADO, inside the intake piping improves gas mpg.