1964 F100 with rebuilt 1 barrel carb. 223 6 cylinder. 3 speed manual tranny. 225/70/15 tires.

Does anyone have any ideas why I would only be getting 8.5 mpg?

Any help greatly appreciated.

 

WOW, only 8.5 mpg? the 223 was known as the mileage maker and has been reported to give as much as 25mpg, check your timing and point gap, did someone put a cam in it? if so your distributor would need a recurve other than that is it geared low? if so maybe a higher pinion gearing would help.

 

25mpg eh, that would be @45mph too.




John

 

MPG comes from many different factors including vehicles weight, transmission type, pinion gearing, tire size, and tuning specification, the old 6 cylinder pre 65 trucks were known to be geared pretty low and were not 70mph freeway cruisers thus with the higher modern speed limits fuel economy will suffer in a low geared truck.

 

I know the speedometer is off at least 10 mph on the low side. Everyone passes me fast and it shows I am going 60 mph.

 

The truck is all original and runs great. It just seems like it needs a highway gear.

 

Jay, Your truck was designed to run about 45 mph tops. Folks did not drive them much faster back then. Would it run faster, sure, but for the most parts the roads back then wouldn't allow it.

We see things a lot different now.




John

 

Thanks John,

Third gear does feel about done at 45 mph. You are right, it will go faster but it sure seems like she doesn't like it. Is there some kind of extra highway gear that can be added to these transmissions? Or maybe some other solution that would be easy. Today coming home from fire station I just drove about 55 ish and she liked that alot better.

 

Jay, Pushing 4,000lbs with that little 223 designed back in the 40s is a lot of the problem.

All manual trannys not overdrive, run 1 to 1 output ratios (tranny output shaft is turning same rpms as engine). You can add overdrive to slow the engine rpms down, but then it may not have the gonads to push it. That is why most small engines had low rear ratios. You have to get the engine power to the rear wheels. There are all kinds of factors on performance, mpg, and mph ratios.

As long as it is in gear, and is in decent shape, you pretty much can't blow it up by mashing the gas. Run it on up to faster speed, it'll just stop gaining before anything bad happens.

Put a 4.6 with auto overdrive in it, and getterdone.

best




John

 

My 1964 f100 has a 223 6 cyl. with the autolite 1100 1 bbl carb. It also has a t-98 4 spd transmission. I few years ago I changed the 4:10 gears to 3:54's and I run 235/75/15r tires. I have everything adjusted perfectly (points, plugs, carb, timing etc.) and the best I can get is 18 mpg going 60 mph on the hiway. I'm thinking that is about the best you can get without overdrive. I also have big side mirrors and i have the tailgate on and closed, so I'm pushing lots of air. I'm thinking having everything set up just close you should be getting at least 15 mpg.

 

My axle code has the code 12 on the door plate
What gear ratio is this?
I also have two parts trucks with the same axle code.
Was this the standard rear axle on these trucks?

Thanks again

 

The only thing I have not replaced concerning this is the pcv valve.

I am unsure if this could have any issues with fuel economy.

 

Put a timing light on it. Rev it up and see if you get any advance. The 223 only has vacuum advance, no mechanical. If the vacuum advance goes bad it will kill performance, gas mileage, and can cause heating problems also.

 

I disconnected the metal line at the vacuum chamber on the side of the distributor and have no suction. Does this mean I just need to replace the vacuum chamber? I have no experience on this portion of the truck.

Thanks again

Jayson

 

Vacuum may be minimal at idle speed and you may not feel it even at higher rpm, its a small line. Check the line for holes or kinks also. Or remove it and see if you can blow air through it. You really need to check that it is advancing using a timing light and the vacuum chamber line connected. Or be on the safe side and replace it, they're cheap. A bad one will kill a 223..