San Diego Ron

What's up with that....and where do I start looking? No sign of any leaks and nothing in oil or water. Right now is sitting in garage, can't afford to drive it around the block. 350 with automatic and car has less than 75000 miles

I WANT TO DRIVE MY CAR H-E-L-P

Jeffery73

Hey Ron,
Nice looking car. My guess would be the carb needs a rebuild. Does the exhaust smell bad?

ratflinger

You sure that no one is stealing your gas?

HO-alts-Rick

69427

I was wondering that, myself. I get better than three mpg with my big block out on track days. Something is definitely amiss here. Good luck tracking it down.

Zulian

My 77 had the same problem except i was getting about 5 mpg, but i found my carb just needed to be tuned out a bit... which i still need to get done lol.

Nowhere Man

rebulid the carb and make sure you have the right size jets

RMS73

The Rochester carb's are know to leaking into the intake through the port sealings, wouldn't think you you get 3 mpg from this. Sounds like the carb has overly large jets/rods or maybe the bowl needle valve seat is not closing, Verify the correct rods/jets and rebuild the carb paying attention to the port seals on the bottom of the carb.
Roger

Tony24

Other than bad mpg, how does it run. What does the exhaust look like? Do you have the smell of gas? When driving does it bog down when you give it gas.

Artsvette73

Put a locking gas cap on.

FB007

Check your oil level. Maybe the diaphram is broke in the pump.

San Diego Ron

I did change over to Elderbrock intake and carb, elimated EGR valve and installed hand ckoke. The gas has not been syphoned, car kept in locked garage and no kids in house to help themselves. Car does run good, has lots of power, but runs rich when cold.

rihwoods

Check:Visual...
#any return lines (if any) from fuel pump back to fuel tank ...
#vent lines from fuel tank(if any) to charcoal canister & check canister itself....
#rubber fuel line at fuel pump.....(assuming mechanical pump)
#sending unit flange on fuel tank..
Possible you are losing fuel on road,but no leaks/smells while vette sits...look for any tell/tale signs of leaks on hoses..

(I had leak once from electric fuel pump below tank,and found leak by accident..already had lousy MPG,so did not notice another gal or so..)

Rich

jaki30

I had a 1973 BB that spwed gas from a cracked rubber S line that runs to the fuel pump from the metal line on the frame. It only leaked with the car running.

San Diego Ron

Now I know where to start looking, I had changed the carb because car was burning too much fuel and wasn't any better after a rebuild.... But that could still be a problem, because I purchased a used one and bolted it on without checking anything. I'll look for any leaks, rebuild this carb or buy new one, do a complete tune-up then see what happens. Car looks good but never had any suspension work done and it is way past due. Even I get it to run right I'm still not going to be able to enjoy it until after that work is done....at least it is California car and the only thing underneath is dirt (no rust).

rihwoods

Keep in touch...

Chris Farrer

I bought a carb and had it rebuilt. The darn thing ran worse than before. It turned out that the float was dry during shipping and must have worn a hole in it and when it was installed the float sank, flooding the carb.
A new float fixed the problem.

C3 4ME

This hasn't been asked, but I assume this isn't somthing that just started happening. You werern't getting much better mileage before and now only get 3 right? Somthing definitely isn't right when tractor trailers get better gas mileage than you.

hwcoop

what rpm is it reving at 60mph? maybe it has 5:14 gears

BigBlockTank

My LS-5 got about 3MPG when I bought it. I replaced the single plane intake (I like to drive on the street) with a GM performance one, replaced the old Holley, fixed all the vacuum leaks and hoses, replaced all fuel hoses from the tank to the carb. I'm about 8-9MPG now, and need to finish tuning as soon as I get an O2 bung welded in to hook up a wide band to.
Keep digging, it takes patience