I have been getting about 7 mpg. Is this normal? I was sorta hoping for around 10. It does need a tune up. And i know when these trucks were made gas mileage was not an issue. Am i complaining about the mpg? No i just want to know if it is normal to get around 7 mpg.

 

The best mileage that I could get was 10 mpg. On the freeway, with 4.10's in the rear, driving 60 mph. Economy in these trucks is finding the cheapest gas.

 

Cranks are 4-5 pounds heavier then a comparable 351W or 350sbc, combined with wedgish port heads, and its a recipe for no mpg.

I recently talked to a guy who built a 390, and after $3500 invested in a gear vendors of topped at 13 mpg doing 65. It was in a F250, bit it had all the bolt ons. A comparable built stroked 351W would of touched 17, and been cheaper. Just not quite the torque. My old C20 with a dead motor did better with lower gears, and no od. Only on gas. The oil consumption was horrendous.

That is why I sold off my FE stock pile, and got a whole car with a fairly lowish mile 4.6 for $600.

 

What do your plugs look like right now? Run a compression test. You want to maximize any engines fuel economy (such as it is) because all that unburned fuel is wasted and will contaminate oil and wear rings and cylinder walls rapidly. Sounds like a 25% deficit in mpg right now?

Make sure the correct OEM size carburetor is installed. The manual will indicate the venturi size, this is important. Too big a carb and it will never run right.

 

The carb is the correct one for this truck i believe. The plugs look like the the truck needs a need a tuneup, and they sorta smell like gas. Is it normal for them to smell like gas? The plugs are evenly worn.

 

Probably not. Gearing is a factor but if you know the mileage that the rig is capable of it kind of indicates the state of tune, it's going out the tailpipe. The good thing is you can do all those things yourself without a lot of hassle. Carb rebuild, fresh wires and plugs etc.

 

I just rebuilt the carb so i dont need to worry about that. Ill give it a good tuneup and see if the mileage gets better.

 

Post a pic of a plug or two

 

If your motor is basically ok you should get way more than that imho. I suggest you give it as much spark advance as it will tolerate - listen carefully for a rattle. You might save money by advancing it to the point where it needs higher-octane fuel but will use less of it.
Eric

 

 

It is hard to start sometimes, and will rattle when it gets tough to start a little. Maybe thats what i need to do. Would you use 91 octane or you think i can get away with 89?

 

Put a vacuum gauge on it. Adjust the carb. Adjust the timing.


You didn't state gear ratio, F250's were geared pretty low, they were and are work trucks.


235-85-16 or 285-75-16 will raise the gear ratio a bit.


Some guys count mileage on one hand, some on two, and a very few on three.

 

I believe the ratio is 4.56-1

 

Thanks for the pic. I'm not too good at determining plug health, these days it's a little tougher with modern no lead fuels. But, it isn't carbon fouled or soaked with oil, can tell that much.

Here's one for example I checked tonight in my 292 after the new stock carburetor installed a couple weeks ago, It had a little bit of extended idle time today, but they look ten times better. I noticed sometimes it's hard to get the color balance to look right in a photo compared to the porcelain. Your plug may be evidence of excessive richness? It looks almost orange. But I'm no expert.

 

The plug in the pic i posted is a little dark for what it actually is, picture quality not that great. But yes i think it is running rich.