Sluggish and poor mpg

[Mv7fd]

I have a bronco ii that has a Holley carb offy intake and msd ignition it's an automatic and it's just really sluggish and the mpg just sucks but the plugs are golden brown and it doesn't have cats it's an 84

 

[alwaysFlOoReD]

Tire size?
Gearing ratio?

 

[RonD]

Could be small gas line leak or filler neck leak, run your hand on gas line and smell for gas, around fuel filter can leak.

Couple of things are used for faster throttle response.
Accelerator pump in the carb gives an extra squirt of fuel into the intake when you push on the gas pedal, this allows for faster response until Jets can catch up to air flow.
The diaphragm on these can crack so less fuel is added.

Not sure what system you have but if distributor has vacuum advance it needs to be hooked up correctly, and correctly is different from model to model.
Vacuum advance can be a misnomer, when you open the throttle more, vacuum in intake drops, but you want more spark advance when accelerating, so on some distributors in might be a "less" vacuum advance, lol.
Check what you have and then make sure it is hooked up to correct vacuum port, i.e. above or below throttle plate, some Fords had an add-on vacuum modulator for this as well.

Check/Reset spark timing, wrong base timing delays responsiveness.

Make sure you are using correct Thermostat temp.
Most Fords after mid 70's switched to a 192-195degF t-stat, this gives better MPG and cleaner oil.
But many still want the old 180degF t-stat thinking it might prevent overheating or ??
It doesn't and won't.
Thermostat sets MINIMUM operating temp, so has nothing to do with overheating.
That being said the 2.8l does have a hot spot in the head because of a design flaw, so make sure to flush and replace coolant every 2 years

 

[kimcrwbr1]

Do you get black smoke when pulling a hill and the skinny pedal to the floor? The big problem I found with mine was the high speed jets were too big and the smaller displacement cannot process the fuel into a vapor to burn clean. The 2.8 requires around 280 cfm max and a 350 holly at 350 cfm cannot properly vaporize the fuel properly in the venturi. If you were to put a 1.08 venturi autolite carb with #42 jets your top end will improve greatly. Or maybe just get some smaller jets for the holly and see if the upper end improves. Also how are you adjusting the slow needles? The 2.8 likes it rich on the idle air mix. Turn the slow needles out for the highest rpm or vacuum pressure possible and the ignition base timing must be exactly 10 DBTDC. Do you have the duraspark distributor with the vacuum advance? Three wires out the base of the distributor?

 

[wildbill23c]

Get rid of the Holley Carb and put the right one on the truck that'll take care of your issues. Sounds like that carb is just too much for that engine, dumping more fuel in than the engine will ever be able to handle.

 

[rangerin]

What Holley carb do you have? Iv'e had a 500cfm one in since day one (truck came with it). If I remember correctly, I have #72 jets in there (or something pretty close to that). It has decent power (what little the 2.8 has) and gets 21mpg with my 5-speed and slightly larger than original tires (aslo has the GM HEI/vacuum dizzy).

Feel free to shoot my any questions. I've only ever had the Holley on the tuck, and have learned how to tune carbs with that one. If you can, do a vacuum check...that will tell a lot.