I have a 1977 Kings Highway RV with a 440 and I would like to switch out the old carb and go with something that will get better gas mileage. Motor has 52,000 miles and runs a 410 gear. I am also planning to put a gear vender overdrive on it soon.

I have no personal experince but the Street Demon has gotten great reviews. Its the best of a Thermoquad, a Quadrajet and an AFB in a modern carb. Suppose to really shine with crisp efficient acceleration.

http://www.hotrod.com/articles/inside-the-new-street-demon-750-cfm-carburetor/

https://www.summitracing.com/parts/dem-1...ASABEgK_CPD_BwE

How big is the motorhome and what are you getting for mileage now?

Kevin

You get the most reliable better gas mileage using one of those self learning EFI kits. I think the underhood heat plays tricks on the carburetor.

The price differential isn't huge when you consider what you are paying for fuel. I'd also look for one with an ignition advance control built in. You can tweak ignition advance on the fly, while the Oxygen sensor adjusts the fuel input to instantaneous conditions.

R.

edel 1406 600 cfm & get the strip kit

You're are fooling yourself if you think replacing a good working carb with a different style is going to do anything for an RV's gas mileage.

But if the current carb is trashed/worn out and flooding a new carb is a great choice. I bet restored to as new MPG is like 8 MPG!?!!

If, no mention was made of that. Mention was only made of increasing gas mileage.

I have some experience with 440 engines and fuel mileage..

Save your gas money.....

The rv is 31 feet long 16000gvw 6 mpg and the carb is a big thermoquad. I don't trust those carbs I have to many issues with them in the past.

OT you might dial in the dist advance subsystems

So, what you really want is a carb you can feel comfortable with.

Well, the AFB clone is simple, less likely to leak and can be had new. A 600 cfm one would probably be perfect for an RV 440.

There are a variety of Holley carbs, but I do not care for Holley carbs.

But for a few dollars more, http://fitechefi.com/products/go-efi-kits/

My 26 Ft class a Ute Liner(11,800 lbs.) had a standard flange four barrel intake on it running propane, I put a Holley #1850 carb(600 CFM) on it. It got 3 to 4 MPG on Propane I didn't jet the carb. and it ran fine with the stock jetting, we lived in SO CA in the high desert(3500 Ft elevation) at that time and drove it all over from the Colorado river(800 Ft.) to the center of Utah(6500 Ft.) and never had any pinging issues with it.
I got between 5.5 MPG and 7.0 MPG towing a 3500 Lb. boat on gasoline and my wife got 8.5 MPG when she drove it with the same conditions
I let her drive it a lot
On your deal I would swap the intake to a AVS or Holley flange carb. and try one of those carbs.
I ended up installing a Eaton two speed rear end in that old chassis, it was 6.17 in under drive and 4.55 in direct, that help a bunch on making it easier to drive in town towing and out of on the road. It had a 4.89 gear ratio in the original rear end with 17.5 inchn rims, I had to swap the rims to 19.5 to clear the rear brakes on the new rear end
Bottom line is it takes a certain amount of energy (gasoline) to move a known weight to go so a set speed at a given MPH
Radial tires can help a tiny bit on the MPG also
A 5.9 Cummins with the proper gear ratio in the rear end and a proper transmission to work well with that motor and weight would help the MPG a bunch, maybe 3 to 5 MPG