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Hi. I have a '50 1/2 ton with a '54 235 in it. I'm pretty sure I have 4/11 rear end. I'm getting pretty lousy mileage - 9 or 10 miles per gallon. Years ago I had a '53 1/2 ton...it got 15 miles per gallon. It probably had a different rear end. Am I getting worse mileage than I should be? Tips? Advice?

Thanks - Big Hank

This post together with the other post about the ugly black soot spot on the driveway says that the carb is running way too rich. Depending on how you drive it you should be getting somewhere around 15 mpg. rebuild the carb.

for the aths southbend trip, which was a good full power round trip run of 1300 miles in my 40. a fresh rebuilt 270, rebuilt zenith carb and 4.56 rear gear i averaged 13.5 mph. with a road speed of 50 and a rpm of 2400.

what do your plugs look like?

51 Ashton... here's a pic of a plug. Looks like the tip of the plug is whiteish

http://i1204.photobucket.com/albums/bb405/kgimbal1/plug.jpg

Thanks for all the advice... I will play with the vacuum/idle

Big Hank

its the alcohol in the fuel.

If you are running a Rochester carb you should check that you have the right base gasket.
The wrong one will block the power valve vacuum port which will give poor gas millage.

Yeah, it's a Rochester. I can read "ROCHESTER," printed diagonally, with BP above and GM below... this is on the front of the Carb. On the back, with a flashlight and a mirror, again I read Rochester GM Carburetor, and a bunch of smaller print that I can't quite read. I've never messed around with the carb at all. Maybe it's time I get a rebuild kit? Or switch it out for a Carter? Again, this is on a '54 235. Here's a pic:

http://i1204.photobucket.com/albums/bb405/kgimbal1/carb.jpg

Yes, model B Rochester.
Besides the base gasket I would also make sure your vacuum advance is working.

There is another issue that can effect your milage calculation. The fuel they sell today evaporates rapidly. If the truck sits for days at a time or even weeks, you can loose enough to change your numbers.
I'm sure there are some that will not agree with me that it will have that much effect. I tried to check my milage a while back and the numbers were all over, tank to tank. It seemed to make less difference on the type of driving than it did the frequency of the fill-ups.

Starting in 1970, most cars had charcoal canisters. They started in varying degrees to seal up the fuel tanks and the carb. The OBD2 systems starting in 1996, actually self test to make sure no evaporated gas can escape. Charcoal canisters used to return the vapors to the carb when the engine was started. Today the canisters are next to the tank in most of the cars I have seen.

No fuel is lost.

Hey guys... OK... I've tuned it up: new plugs, points, condenser, rotor, cap. Timed it and adjusted the valves. The motor sounds good, but I can't imagine that i'm going from 9 to 15 miles per gallon. (Speedometer is out, so hard to know for sure). I talked to a guy here in town who told me to definitely rebuild the carb. He said if I don't rebuild it ($20.00 for kit), then I will most definitely need to rebuild the whole engine sooner or later ($2000.00). So, I think that's my next move... meantime, the ride is smooth and sweet! Hadn't been tuned up in years - mileage issue or not - the truck is running nice right now. More comments on the lousy mileage - wear and tear on the motor issue?... Thanks, Hank

One question; if you have no speedometer then how do you determine the mpg? Are you guestimating or running a tankful of measured miles?

Here's what I did: filled the tank - checked on my Iphone GPS application and plotted a course to a high school about 10 miles away - turned out it was 8.3 miles away - drove out there and back - 16.6 miles, and refilled the tank. It took 1.6 gallons. The math tells me I'm getting 10.375 miles per gallon. That was a straight highway run, going probably 50 - 55 the entire trip. So, although that's better than the 9 MPG I thought I'd get, in-town driving would probably be around 9. So - carb rebuild? I guess so. If you guys with a 235 and a 4:11 rear end are getting 15 MPG, I must have something seriously wrong with the carb, or I have an even lower geared rear end than 4:11. The project continues, with your tips and suggestions... Thanks, Hank

I have a 54/235 with fenton headers and offy intake with 2.73 and a t-5trans also 235/75/15 tires. in town i get 12-13 mpg. on the road in 5th gear i average 20 mpg, and i have seen a high of 23 mpg driving at 70 with the cruise on. these are documented and calibrated speeds. i got 17 going over the mountains in WV in April.

big hank, that's not an accurate mileage test.

Pumps don't always fill the tank the same way. Drive 100 miles or more and fill up. You have less percentage of error as the miles driven and gallons used ballance out better.

Could I please ask you what size your tires and rims are? 2400 at 50 sounds great, but to get there with a 4.56 you need very BIG tires (diameter I mean).

7:50 x 16.0, 30.5" tall. actually its 2512 rpm acording to the speed/rpm chart. my tach holds a steady 2400-2500 at that speed and the gps agrees with the speedometer and rpm/chart.

UPS just delivered the Rochester Carb rebuild kit. Gonna take a few pics of the carb on the truck, then remove it and begin. If the carb has really been the culprit with my lousy mileage, should I see visual evidence of the reason why, once I get the carb apart? Gunk? Clogged areas? Poorly fit gaskets? I'm just wondering if there will be an 'a ha!!" moment.

Thanks,

Hank

The carb is now rebuilt! I think I found the culprit - the old pump plunger has a leather seal around it, which is no longer properly in place (see pic). The rebuild kit came with a new plunger and seal - will check my mileage. Hoping the replacement part will make a difference.

Hank


http://i1204.photobucket.com/albums/bb405/kgimbal1/carbpart.jpg

Dramatic results.... can't be sure because gas pumps are not all the same, but this time I filled the tank, drove 40 miles, filled it up again (same gas station)....only took 2 gallons. I don't believe I'm getting 20 MPG, (I was getting 10), but even with a big margin for error, mileage is greatly improved. I will have to do a more scientific test, but I'm happy with the results of the rebuild! Thanks guys, for your tips and advice.

Hank