just purchased fuel milage horrible

[jking006]

hello all,

not sure this is the right place for this post.
A friend of mine just bought his first RV. he has always owned travel trailers and set them up in permanent camp grounds.

bought a 1979 class c holiday rambler on a ford chassis. Has the 460 with a C 6 transmission with 3.73 gears. also has the "tag" axle.
all emissions have been deleted by previous owner and a after market holly carb and K&N filters. duel exhaust.. runs great!!!
this thing got 1.9 mpg driving 60mph for 50 miles on the highway!!
i cant imagine that is what it should be considering my 1982 gets 8 mpg with my heavy foot
everything is in order under the hood. only thing i haven't checked is the timing or looked at the size of the carb. it is a holly double pumper.. no sign that it running rich tail pipes are clean as to be expected and no fumes.
any one have any ideas??

[midnightsadie]

after you find the problem,let us know ,even hot rods get better mpg.I like the though of dual tanks. or a major leak.

[jking006]

K Charles wrote:
I also had a 1976 f250 with a 460, it got 10 or 12 MPG going to work or carrying a big old pickup camper. Did it ever shift into high gear?

transmission shifts in all gears no slipping or anything.. i forgot to mention it only has 44,000 miles.. but i know its 37 years old.. to compare it to a 3/4 ton pickup isnt really fair but.. i do have a 1982 ford tioga rv that does have a bad carb and it gets 8 mpg and ive got a heavy foot it also has the 460 and a C6. but his does have that 3rd axle under it.. but i still cant see it haveing that much of a difference

[bdpreece]

Are you sure it does not have two tanks and you filled one and then ran on the other one? I had an old class A like that once, when it coughed you had to manually switch tanks.

[K_Charles]

I also had a 1976 f250 with a 460, it got 10 or 12 MPG going to work or carrying a big old pickup camper. Did it ever shift into high gear?

[jking006]

I just went out and pulled the oil dipstick.. right on the full mark and no gas odor or taste either!! no signs of a fuel leak anywhere i looked for that when we got it home..

i know it used that much gas because it was on E when we got it.. went to the nearest station and put 24 gallons in it.. or 50 bucks at 207.9 a gallon.. drove 50 miles and ran out of gas!! tank was bone dry i even laid on the ground under the gas tank and had my friend shake the rv to listne for gas to slosh around in the tank

[Old-Biscuit]

How did you determine it used 25 gallons in that 50 miles?

Had a 1975 F250 460CCI. (385 motor)
It got 5 mpg
Due to emissions engine had been detuned (timing ******** 8*)
R E T A R D E D is blocked?

Timing was SET BACK 8* as in opposite of Advanced!

Changed cam/crank timing gears to pre-detuned, 4 bbl Carter and set of headers.
Mileage went to 10 mpg regardless of how I drove it or loaded it


On Edit:
Yes ........mine was a P/U not a Class C but Ford 460 (385 motor) was same whether it was in a truck/RV/boats and 1972-1978 were detuned.

[dodge_guy]

If it were that bad it would be running very rough and belching out black smoke out the tailpipe. Either that or it is leaking fuel badly. It is possible the fuel pump is bad and it is leaking into the crankcase!