The Stovebolt Site Forums The Parking Lot Big Bolts Updrafts and Gas Mileage???

I took my first trip into town a week or so ago in my COE. I wasnt as happy with my fuel consumption there and back. Im roughly guessing I was running about 6-7 miles to the gallon. Is this be normal???

My valves are adjusted properly, I just gave her a tune up. Close to proper amount of air in the tires. I ran the numbers and never had her over 50 mph, and I figured at 50 with 36" tall tires and a 6.17 rear gear she was turning at about 2800 rpms.

I know shes pushing a lot of air, weighs about 5K pounds, and is running on a 60 year old engine, but I was still guessing Id get closer to 9ish mpg, just thinking of what I get with my 216 in my chevy.

The piston in the carb is adjusted to the middle notch. Would it be worth adjusting it to the lower notch so less fuel is being pushed on acceleration? Or would that just kill my power when stomping on it? Its a 63AW11 Zenith on a 248.

Thanks, Jeff

Another consideration would be dragging brakes.If a wheel is not fully released after braking it's like dragging your foot on the ground. Following a run, check for heat on the drums, or jack up each wheel, apply the brakes, release, and immediatly determine wether the wheel revolves easily. My motorhome vexed me for the longest time (6-8mpg) until a quick stop on a greasy road revealed left rear wheel drag. Fixed that and have 10-11mpg. It's like life - the little overlooked things drag you down. :o)
Laurence

Jeff,

I assume that the gas in the tank is not as old as the truck?

Dallas

I don't think you will get much better than the 6-7 mpg you are anticipating. Also, I would leave the accelerator pump where it is. The discharge doesn't change much with the different positions. My '52 flat-bed would get 6 mpg up hill and down, 'fast' or slow, empty or loaded. Empty, it did a little better, but 'empty,' it still had an air compressor on the back that probably was about the full rated load for the truck. The compressor also had a 6-cyl engine. A good tail wind and long down-grades helped.

Harvester

Further to tracking the poor mileage, I'd determine the exact consumption prior to tearing my hair out. Connect a gallon can direct to the carburetor (not the fuel pump) and drive the truck until it coughs out; re-fill, and drive back the same way. Note the mileage. That's a start point. Next, pull the plugs and examine the porcelain. Plugs are the 'eyes' of an engine. They will very often reveal problems associated with particular malfunction. Check also the tail pipe residue - heavily carboned, damp, points to unburnt gas. Another step is to re-check fuel pump pressure. Old, or new, pumps are notorious gas wasters if not operating within specs; and a leaky diaphram can really affect consumption. Then too, is the carburetor itself. From float level, to needle seat, to dirt, many little things plague carb function. But that's part of the fun(?) to be had with these vehicles - chasing down the gremlins and tweaking every part to wring best performance. Plus, when everything is perking, guess who gets the bragging rights at the next mileage swapping tales? :o)
Laurence

Ive gone through the entire fuel system and there shouldnt be an issue. Even if the fuel pump is faulty, the gas tank will gravity feed the carb since its 3-4' above it. The plugs are fine for an old engine.

They way an updraft carburetor works is by engine vaccum. Thats why I was asking about the vaccum piston adjustment. As you open the throttle to gain speed the engine vaccum drops and the piston falls downward giving you the squirt of fuel needed. There are 3 settings for driving conditions or altitude adjustment and I imagine it could make a world of difference how efficient it could be.

I was hoping someone with more experience with updraft carbs and COEs could step in and give their experience on what to expect.

Thanks, Jeff

All carburetors function under engine vacuum - regardless updraft/downdraft configuration - unless they are turbo-charged; and even then vacuum plays significant role. The piston adjustment to which you refer is part of the carburetor accelerator circuit; one of five such systems contained in that device. The piston only moves during sudden drop in vacuum (or on some carburetors in combination with designated linkages) hence the 'accelerator' descript. Normal - not 'lead foot' - acceleration does not see that circuit operate. However, on a rough road, with your foot jabbing the gas pedal yes, conceivably, there could be unintended spurts of gas emitted from that system. But, under smooth acceleration and steady speed such does not occur. Setting for pump stroke (the three holes) simply allows more - or less - fuel to be introduced into the carb throat upon stomping the gas pedal. I don't see excessive gas consumption there. And a COE is not really a candidate for jack-rabbit take-offs. :o)
The vehicle's gearing, as mentioned by Harvester, bears directly upon its fuel consumption, as does its overall weight. As you've indicated, there appears nothing amiss with the fuel delivery system, brakes, air filter, leakage. My only suggestion would be a tip I received from a RV owner: "Drive as if you've an egg between your foot and the gas pedal." I tried that - wiped up the mess - then installed a vacuum gauge. Keeping its needle in the green zone is half the fun of RVing. And with gasoline up here currently at $5.53 per gallon (and rising) I am very cognizant of fuel wastage. But every little tweak is bound to help and, as mentioned, that's the challenge of driving a Big Bolt. Good Luck with COEy.
Laurence