82 F-150, 300 six, not very many mods and has always made about 16 mpg.

Well today on an outing it did very poorly on gas, i filled it to a half tank and set out, going less than 10 miles, traveling at a constant 45 mph.

Once i arrived at my destination it was showing that i had a quarter tank left, and stayed on a quarter when i went and ran some errands, and i came home on that very same quarter without the guage moving.

The carb is in fair condition, with one ailment, it appears to be leaking gas around the top of the carb, where the air horn bolts down to, that and the choke doesn't work, meaning i have to do an underhood scramble when the truck is cold. Other than that its fine...

Can anyone explain this?

 

That gauge is not perfectly linear in relation to the amount of gas in the tank even when it works perfectly, and on a truck that old, it probably has some bad spots on the sender that make it more erratic. It didn't burn any more gas than it normally does, but you should fix the bowl leak or you'll be doing an out-of-the-cab-away-from-the-fire scramble.

 

If it hasn't caught fire yet it probably won't under similar conditions. Gas has a tendency to flash off/evaporate before it actually catches fire (hense then need for a spark plug in gas engines).

You should still fix it, less the altenator/choke/battery/etc. create that spark. The hood doesn not work as well as your piston heads in containing explosions ;-)

 

i solved the problem by rebuilding the carburetor, its back to running normal, it idles much better and its got a lot better throttle response.

a $13 dollar carb kit did the trick for me.

 

Gasoline CAN'T catch fire until it a) evaporates and b) mixes with oxygen. But even after both those, it still has to reach a critical temperature before it will ignite, and THAT'S what the spark is for. The spark plug has nothing to do with evaporation.

 

i am terribly dissappointed with my truck .it has the efi 302 and it runs ok.but i only do around the city driving and it seemed that it was getting crappy gas mileage but i kept ignoring it and took a 125 mile round trip not too long ago and it was 65mph all the way up and back and i filled the tank till it stopped the pump and brought the gauge past the full line as usual the night before it took 21.00 from close to e which the guage is obviously not totally accurate but it is how i judge it .so anyway 21.00 worth of gas at 1.56 a galoon is about 13.5 gallons and at the end of my journey it was back at the E mark so assuming it used just that 13.5 gals and none of what i cant exactly tell is left in the tank besides that is works out to be about 9.25 miles to the gallon.now i am no rocket scientist but i think theres a big problem with that!

 

>Gasoline CAN'T catch fire until it a) evaporates and b) mixes with
>oxygen. But even after both those, it still has to reach a critical
>temperature before it will ignite, and THAT'S what the spark is
>for. The spark plug has nothing to do with evaporation.

I think you misunderstood what I was trying to say. I was implying the heat produced by the engine evaporates and heats the leaked gas, but it won't burn even if the gas vapor reaches engine temperatures. That's because the "critical temperature" (as you put it) is greater than the engine temperature (for atmospheric pressure).

 

OK I can go with that.

 

I have a Holly made 4 BBL on my 84' F-150 351. Original carb. Would re-building my 4BBL be a difficult re-build to take on myself? I've done a few 1 or 2 BBL carbs in the "way" past, and am pretty comfortable working around my truck.

Scott
Vashon,Wa.

 

I personally have no idea. I've only worked on my 2 barrel

 

Hi-
Ssvashon5 go ahead rebuild your holley 4 barrel. I don't think an easier carb to rebuild was ever made. For holleys, theres really no difference between the 2 or 4 barrels.

Pancake do your test again but bring a container with a couple gallons in it and drive it untill it runs out of gas. My trucks just about the same as yours tuned up good it only got 11 or 12 mpg, even now with electric fans it's only doing like 13.

 

I have an '86 F250 with a 351W HO and 4 bbl Holly/Motorcraft Carb. I get terrible gas mileage and it's a b*tch to start on cold mornings. My question is, would I be better off going with a new Holley 4160 600 cfm or rebuilding the current 4180 carb. By the way what's the cfm rating on the stock carb and would taking off the emisions equipment have anything to do with the bad mileage??? Thanks a ton.

 

Sounds like you've already got problems - don't make more by removing things until you've got it running right. In fact, you'll make your life easier for now by making sure everything is put back because there are books & websites that show how it works if it's all OE & hooked up. If you have things missing, you'll never learn how the engine is supposed to work or how to get it working.