I had the Rochester 2 barrel carb completely rebuilt about 16 months ago on my '59 Olds Dynamic 88 with a 371 CID engine. After the rebuild, it was still stumbling somewhat, and was re-adjusted again. The problem is, I am only getting 3 mpg. Can't say what it was prior to this, as I had just acquired the car shortly before that. The car starts and runs great. Should I be concerned about this?

 

I'd look into it, is this an around town fuel mileage or highway?

 

Seems a bit low to me.

Are you sure your odometer is reading accurately?

- Eric

 

Something don't sound right.I had a 34' Motorhome with 3 slide outs that got 8 MPG on the highway and I thought that was bad. Larry

 

You might want to check your oil level and be sure your gasoline is not getting into the crankcase. I've known this to happen. Larry

 

That was my biggest concern, Larry. However, the oil level isn't rising, and the oil on the dipstick doesn't smell of gasoline. I went to a car show last fall that was 35 miles away. Left with a full tank, and ran out of gas on the way home. Since then, I fill up any time I take it out. Last run (in town) was 25 miles, and I used 8.3 gallons. The odometer is recording correctly.

 

I have run out of ideas ,but I will ask around. This is not typical.I've owned many Oldsmobiles and never heard of one not getting decent mileage. I had a '59 Olds that we went to Daytona in,and at the rate of gas mileage you are talking about,I would have had to get a mortgage just to buy gas for vacation. Larry

 

I'd check and make sure everything is functioning correctly with no vacuum leaks. Look down into the carb while its running and see if its dribbling fuel, smell the exhaust and see if its running rich, make sure the dwell/timing is right and the advance is functioning. Pull the plugs and see what they look like and hook up a vacuum gauge and see what the reading is.

 

it's hard to believe it could burn that much fuel and not be blowing black smoke out the pipe like a diesel or fouling plugs. retarded timing and no advance can greatly affect mileage.i know you said since carb rebuild but it might be worth checking

 

Who rebuilt the car? Do they have any ideas/opinions on the abysmal gas mileage? Something is most definitely amiss!

 

3 mpg can't be right. That fuel has to be going somewhere other than combustion.


Pull the filter off the car & cut it open & look for fuel contamination.

 

Thanks to everyone for their suggestions. I will definitely stop by the shop that did the rebuild and discuss this with him.

Dave, if I cut the oil filter open, what should I be looking for that would point to fuel contamination?

That is my biggest concern....driving the car like this if it is causing damage. It does run rich for a couple of minutes when I first start it up, but that clears up right away.

 

Check to see if you have rubber fuel hose between the tank and the steel lines, and in front between the steel lines and the fuel pump. These can be old and cracked and leak fuel. Who built the carb and did they know what they were doing? A 2 barrel is simple. Something is definately not right.

 

This problem has to be a gas leak or a faulty Carburetor.I would check everything for leaks, then I would be looking for a different Carb. There's a rebuilt Rochester 2 barrel on EBay for a 1960 Olds. For $130. As stated above ,these 2 barrels are simple and usually don't give any problems when rebuilt. Wouldn't take long to recover $130 if your mileage came up to 14/15 mpg like it should be doing. Or maybe someone on the site has a 4 Barrel intake and carb they would sell you reasonable. You might also call Mike's Carburetot Restoration and just tell him your problem and get his ideas.The number is (360-347-1077) in Rochester Washington. Best of luck and keep us informed. Larry

 

Leaking somewhere. When you get to where your going is the rear bumper and rear end kinda oily? Look under the car for oily greasy gas smell. I would definitely look for leaks.

 

Sorry, I have to correct this.

Rubber fuel lines between the tank and the pump can definitely crack and leak, but, as they are on the suction side, any minimal leakage that still lets the engine run will do no more than coat the surface of the hose with a layer of fuel, which will be easy to smell, but won't do much more.

Once you have a large enough leak for any amount of gas to leak out, the car won't run, as the pump will suck air and lose its prime.

These rubber hoses are a frequent source of problems, and should always be inspected and usually replaced, but they would not cause this particular problem.

Also, any leak that would reduce mileage by this much would leave an actual puddle somewhere, which would be hard to miss (I've had cars that leaked gas "back in the day," and I can tell you that a tiny amount will make a BIG puddle, and still won't noticeably affect mileage).

- Eric

 

Three mpg is some damn good engineering.

Oil companies might want to study that engine closely.

Generally, if one tries to flow that much fuel thru an engine, it will choke to death and stall. Foul the plugs out.

 

I agree with others that it has to be a leak somewhere. There is no way that engine can possibly burn that much gas. It would have to flood out. The strange thing is there should be a strong smell of gasoline. This is a weird one.

 

Not weird if there is a flaw in the calculation of miles traveled.

Also, I can vouch for the fact that it is possible (though highly unlikely) to get that kind of mileage, under the right circumstances - In my younger days I drove an ambulance. We usually drove big Southerns with dualies that weighed in at about 10,000 pounds, and were powered by 454s. They ran 24 hours a day, 7 days a week, and were either idling, driving in stop-and-go heavy traffic, or had the pedal to the metal, shifting the TH400 manually at the redline. There was a fuel log we had to fill out every time we gassed up: Date, Time, Vehicle number, Mileage, Gallons. I noticed that the difference in mileage was pretty much always the same as the number of gallons, that is to say, we pretty consistently got 1 MPG.

So, yes, you can get that kind of mileage, but only under pretty extreme circumstances.

- Eric

 

Just an update for all of you who were so helpful with your suggestions.

Appears to be a couple of problems with the car. The guy who originally rebuilt the carb checked again and found the carbon at idle to be 4.5%. He adjusted the idle mixture to .5%. That bumped up the mpg to about 6.

After that, I was fueling up the car to head to a car show and the guy at the next pump pointed out that fuel was dripping from near the rear axle just as the pump handle shut off. Turns out the gasket was bad at the top of the fuel tank sending unit, and the vent hose, filler neck hose and fuel supply hoses were either rock hard or deteriorating. Hard to believe that these things could impact gas mileage so much, since they should not be an issue once the fuel level dropped in the tank. However, once they were all replaced, my last fill up recorded 11.1 mpg.

Still not totally satisfied, as I now have some stumbling issues and backfiring through the carb on acceleration after I have done freeway driving, but at least the main concern has been addressed. The rest I can live with. I'll just stay off the freeway!

Thanks to everyone again.

 

Glad you're making progress!

- Eric

 

The backfiring is a concern which could mean possible valve/cam issues. The idle mixture screws have nothing to do with off idle fuel economy. The leak at the tank probably is the big contributor to your issue.

 

Thanks for coming back and giving us an update. We don't often get those.

Good luck with that big ole cruiser.

 

11 MPG isn't that terrible, with a 324 on a long trip I only averaged 13 MPG, some hills and a head wind for a day didn't help much. GM wasn't very much concerned with mileage at that point and time. Gas was about 35 cents a gallon in the early sixties.... Tedd

 

So if we're talking about that beast in the picture, which must weigh 5,500 pounds, with a slightly larger 371 motor, 11mpg may be the best you can get.

- Eric

 

When I was 16 I had a 64 Buick Wildcat convertible with a Rochester 4bl my Dad and I rebuilt the carb. Well something was not right and I believe the float may have been stuck. I got exactly 3 miles to the gallon. The worst part is you need to be cautious about backfiring through that the carb, Mine caught fire and burnt to the ground. Apparently Rochesters were known for that. That's when I discovered what insurance is for.