Motorcraft/holley 460 carb questions (long)

I bought an old 1983 E350 class C motorhome 4 years ago that had been sitting 8 years. I got it home and fixed the coach. I started it and carb was leaking out accell pump so I replaced that and needle seats. It would run ok and got about 7.3 mpg but would not idle. I made one trip that way. It had bolts broken off in the head from the manifolds. I pulled the heads and sent them out to have bolts burnt out. While putting it back together I found a local guy who had brand new Dougs headers just made for this chassis. Even had the small y pipe to hook it to factory exhaust . I also installed a Flowmaster 50 series muffler. I put them on with the heads . I was trying to pick up one mpg. In the mean time I found a brand NEW Ford Motorcraft carb not a rebuilt on ebay for 200 dollars. I bought it and installed it also. After doing so I noticed it had one letter off in the suffix. I took it on a 2500 hundred mile trip and my mileage dropped to 4 to 5 and now I have no power. Truck has new motorcraft cap rotor and wires at same time. I just replaced the distributer due to it being frozen in the block and I have timing set with as much timing as she will take. It will go 55 no problem but you have to take your time. I am leaving on a 1100 mile trip and I know it will make it but... Is maybe the carb I put on for a 5.8 and not big enough? Did the headers lean it out too much? I still have the factory carb. Should I go through it and reinstall? This week I found leaking egr spacer gaskets and ix that and it starts and idles better then ever. It is fine at 55 not does not want to pull even the smallest grade. Another new carb is not in the budget. I had an identical motorhome years ago and it always got about 7.2 mpg and had all kinds of power. it also has new fuel filter and two new in tank electric pumps.

OK, I will answer myself. The carburetor I put on was too small. I went through the other one and My power is back. Wishing I would have done this two years ago.Hoping to save 200 dollars in fuel. Waiting to see tomorrow how my gas mileage is with the headers. Leaving for Tennessee and hoping for a nice trip. Anyone one want to buy a low mileage like new 1983 5.8 carb?

If you care 7.49 mpg towing a Ford Explorer. Plenty of power

That's great, glad you found your problem. I would have thought the opposite. When I first read your post, I thought you might be heading my way. Had a cold one waiting on you.

I was supposed to be your way last month. My uncle remarried and my niece graduated high school, but my oldest son got mono and could not leave him at home. We are going to make it out there this fall or late summer. Havent seen mom since thanksgiving. My sister from down your way met me out here. We traveled to Niagra Falls last year and I picked up my lil sis in Meadville. Camper was at 4.5 mpg! 7.5 was a nice surprise. already saved 200 dollars on fuel!!!!!!!

Believe it or not, some very mild portwork on the heads (in the interest of port flow efficiency and not all out drag racing ports) while they were removed from the engine would have increased fuel mileage to over 8 mpg for sure.

Next time,

Paul

I never thought of that. Oh well next one.

Originally Posted by gbic1

Anyone one want to buy a low mileage like new 1983 5.8 carb?

Could you please post all numbers on air horn.
And or sides ?
You say its brand new never opened up ?

Originally Posted by paulkane

Believe it or not, some very mild portwork on the heads would have increased fuel mileage ......Paul

What and where would you grind and why,?....
I ask alot of questions cause im into confirming old how to's and learning new techniques.

Im guessing its an automatic, and maybe a slightly lower rear end gear ratio might help,?
Just a thought.

Thanks.

Carb was brand new never opened when I installed it two years ago. It has about 4000 miles on it. Lower gears are not a option becaue it is heavy and I tow with it, I will post list number tomorrow.