Re: BAD gas mileage.

by pila Mon Jun 13, 2011 10:02 pm

If it's the 2-bbl 2GC, they had worse mileage than the Q-jet, mostly because of the small primaries of the Q-jet, from what understand. GM got away from the 2bbl because of that, from what I've read about the subject. I believe the Q-jet is the best street carb, for all-around driving. The Holley on my Malibu works great, but it likes gas to the tune of 9 MPG. Thought about getting a Sean Murphy Q-jet for it.

by texan01 Mon Jun 13, 2011 10:15 pm

Mine is knocking down 15 and 20 in normal driving with the 305 and the 2GC. Q-jet could probably kick that to 16-17 and 22 if I keep out of the secondaries. The Q-jet is the superior carb in all honesty.

That swap is in the works, but I'm waiting until I'm ready to do a rebuild on the whole mess, since it needs valve stem seals, and I've got a set of big-valve late model 305 heads to swap on, and If I pull the heads, I might as well pull the pan off and re-ring it since its got 150,000 miles on it. And and and and and.

In otherwords, I'll live with the 2 barrel till I'm really ready for a rebuild.

The 2-jet is really a 1950s design, obsolete even by the standards of the '70s. Just a bigger bore version of the carb that came on the original 265 in 1955.

The Holley is a similar vintage design. Both work, and both give mediocre mileage, one gives great power. Both are dead simple to work with.

by 74MonteCarlo Mon Jun 13, 2011 10:46 pm

I'm not putting on a Q-Jet lol. It got great mileage BEFORE the engine was removed and repainted.

I have a Holley 2 bbl off a '76 Chevy Van. Wont work on mine though.

by BlackChevelleSS Mon Jun 13, 2011 11:02 pm

I would check for leaks, maybe its leaking just enough to evaporate and not show up obviously, check all rubber hoses and connections.

by texan01 Tue Jun 14, 2011 8:00 am

I got to thinking, I had a carb from my 76 that I had sitting on the shelf for 10 years, and the original carb on the 77 had some major issues with the choke and idle quality. I swapped the carbs out, fully expecting the carb that was last rebuilt during the Clinton administration to give me fits. It worked great, sawdust and all on it.

It's still seems to me you've got a major fuel leak. Like either the float is stuck and is flooding the engine, or the fuel pump is leaking internally into the engine.

by abajc3 Tue Jun 14, 2011 8:20 am

wouldnt the oil smel like fuel if it was leaking into the crankcase? reason im asking this is because my mileage isnt that great and i know the pump is weak. i just ordered a new one, ill see.

by 74MonteCarlo Tue Jun 14, 2011 9:14 am

I've smelled the oil...does NOT smell of fuel.

by texan01 Tue Jun 14, 2011 4:46 pm

Smell isn't exactly a good sign. Mine didn't smell since engine temps are hot enough to evaporate the gas in the crankcase. It also has fresh air drawn in continuously while the engine is running thanks to the PCV system. I finally noticed mine when I was tuning it up, and had it running, and saw the puddle of gas under the car with it running, it had finally bled past the vent on top of the diaphragm.

Sounding like it's a possible fuel pump, or a stuck float in the carb, take the top off and check to make sure the float moves freely. You shouldn't need a new gasket for the top but kits are cheap as well.

Performance is good? Mine had a bad vacuum advanece and ran great, just had so-so power at part throttle, but would pull well at WOT.

by ant7377 Tue Jun 14, 2011 5:16 pm

Maybe the dist loosened up a little check your timing might be to far back and thats causing the problem. Give it a little more while you are at it, the factory spec is not enough anyway.

by 74MonteCarlo Tue Jun 14, 2011 8:27 pm

Timed at 12 degrees.

8 is factory

by 74MonteCarlo Tue Jun 14, 2011 8:34 pm

O'Rielly has a fuel pump for my car for $18.99.
Jus' gon' bite that damn bullet, and get the sum'bitch.

by 74MonteCarlo Sun Jun 19, 2011 4:29 pm

Welp...new fuel pump is on. Oil was nasty from the fuel leaking in it. So, I changed that and put a bottle of Seafoam in the fuel tank. Timeta jus' sit back and wait... silent

by Sponsored content