I have a 1984 Ford F250 with a 5.8 351 engine. It has a 2 barrel Windsor carb on it. I am currently getting only about 8 mpg. I have replaced the spark plugs, air filter, and spark plug wires. These replacements have not had any effect on the mpg. I did notice that there was a fuel leak coming from the accelerator pump so I replaced the pump diaphragm. I just want to point out that the fuel leak was not a lot. There was some fuel build up on top of the engine under the accelerator pump, but it was not a fast drip. I just replaced the diaphragm today. Not sure if that will have any effect on the mpg yet. I also read somewhere that disconnecting the accelerator pump would increase mpg, but it would effect acceleration and performance. Any advice on that?

Does anyone have any advice on how I can increase my mpg? Please help. Thanks.

 

tire pressure, stock tire size, correct gears.

proper carb settings, proper timing, all systems functioning as they should (emissions, evap, pcv, etc.)

drive like there's an egg under the gas pedal you dont want to crack...

slow down on the highway.

 

Don't disconnect the accelerator pump. You won't like how it would drive. Drive with
a lighter foot and be real smooth with acceleration and take offs and you will get better
fuel mileage. Also check the timing and make sure it is set to spec. You can sometimes
increase the timing to help mileage but be real careful about too much timing will cause
spark knock.

 

Thanks for the advice. I do already drive very light-footed. I normally don't drive on the interstates and mostly drive under 55 mph. I don't accelerate quickly and try to be as easy as I can on the peddle.

Question about the "stock tires" comment. What does that mean?

Also, the carburator doesn't have many of the vacuum lines connected to it. I believe the previous owner disconnected them or removed them. The A/C was removed from the truck and most of those lines were removed or plugged off. I asked the service department at the Ford dealership about the vacuum lines and he said that shouldn't have much effect on the system with that type of engine. Is that correct?

 

it will if the lines arent capped.

large tires increase rotational mass, unsprung weight, rolling resistance, are harder to push through the air at speed, use more fuel, and require the engine to work harder then stock tires.

Skinny tires, properly inflated will get better mileage.

matching gears to tire size will help by increasing mechanical advantage, but too low of a gear will cause the engine to spin too fast and too high of a gear will cause the motor to bog...both situations will cause excessive fuel consumption.


if you've already changed all the parts and gapped plugs correctly. Then check timing, adjust carb, change air filter, and tire inflation.