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Old 11-20-2012, 01:39 PM   #1
fratelli
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7 mpg! What is wrong here...

Put a couple of hundred miles on my '81 Vette. It's got headers and the cat has been cut out with true duals out the back. It is really sucking fuel, something is wrong here. I'm guessing swap out the fuel filter and look for leaks, the carb is overdue for a rebuild, something like that. My nose tells me it is running a bit rich. I know they get bad mileage, but 7 is beyond bad. Any ideas?
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Old 11-20-2012, 01:49 PM   #2
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When was the last general tune up? Plugs, wires, cap, rotor, filters of all types, carb cleaning/rebuild.

Timing good?

I am sure there are other things and I am curious to see what others say.
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Old 11-20-2012, 01:50 PM   #3
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Follow your nose. Smells like time to rebuild your Q-Jet.

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Old 11-20-2012, 03:10 PM   #4
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Rochester carburetors regularly have an issue with the lead plugs at the lower end of the main jet well. You have to take the throttle plate off to see them.

I cleaned and JB Welded quite a few of these over the years to fix fuel leaks. The leak is a drip but over a tank of fuel a fair amount of fuel can leak out.

It's easy to test, with the bottom off and the open bowl supported on wood blocks fill the bowl about half full of fuel. If they are leaking there will be a small puddle of fuel in 10 minutes or less.

Could be a tuning issue as previously mentioned but my guess is it's carburetor rebuild time. Considering the cost of having a carb done right and you're concern about fuel consumption. Perhaps it might be a good time to think about upgrading to fuel injection?

After all Christmas is coming up.............
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Old 11-20-2012, 04:25 PM   #5
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turn back the fuel mix for a quick fix?
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Old 11-20-2012, 08:19 PM   #6
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That's probably about what Ol' Red gets. But in reality, I'm feeding a lot of cubic inches and making some fairly large HP numbers..

You should be up in the mid to upper teens at least. I'll bet your carb needs some help.
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Horsepower is like potato chips. If you have 300, you want 500. If you have 500, you want 800. One is never enough.
Old 11-21-2012, 06:23 AM   #7
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No point in even touching anything unless your ignition is working correctly.
Check your distributor timing, dwell, mechanical, and vacuum advance. Also wires, cap, points, etc. the standard tuneup stuff.
Then go to the induction/fuel system. What engine, cam, induction, carb, etc. are you running?
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Old 11-21-2012, 09:46 AM   #8
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Thanks for all the advice. Thing is, the car starts and runs wonderfully. Turn key-boom on, idles at 900 all day. Sounds beautiful and responds well too. My mechanic suspects the carb as well and he too mentioned fuel injection. I was thinking I could fix it by putting an LS7 motor in there. Might be a little more expensive though. Mechanic can't get to it till spring, I'll update you then. Thanks again.
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Old 11-21-2012, 10:29 AM   #9
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Hoo yea! on the LS7. I assume you're talking new generation LS7. That is a whole other world of power, weight and economy.

If you're talking the 460 HP big block then gas mileage is about the same as your getting now. My '69 435 HP car got 6 mpg on a good day.

Keep us posted on what you decide.
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Old 11-21-2012, 12:19 PM   #10
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Obama says check your tire pressure.
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I'm taking care of my procrastination issues, just you wait and see.
Old 11-22-2012, 12:35 AM   #11
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The tire pressure thing is good advice, thank you. I don't think it could account for this much of a loss, but still. It's a safety thing too. I would of course be dropping the new LS7 in there! That thing is wicked. Maybe I can wait for someone to crash a 2013 model and get the first C3 with the new LT1 drivetrain.
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Old 11-22-2012, 05:18 AM   #12
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BEAUTIFUL CAR!!
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Old 11-22-2012, 06:52 AM   #13
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Quote:
Originally Posted by blckslvr79 View Post
Obama says check your tire pressure.
That's a no-brainer and has been around long before Obama.
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Old 11-22-2012, 09:51 AM   #14
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my experience....gas leak. though I have a high pressure fuel system that was going through TPiS crappy (cheap) fuel system.
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Old 11-22-2012, 10:08 AM   #15
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Take a look at Mast Motorsports for the LS7. Complete crate, with all the cool parts, computer, wiring and already tuned on the dyno.

7 wire hookup, fuse panel, electronic throttle and all the sensors. The horse power and torque is amazing.

After comparing options this is what I ended up getting. It was cheaper than buying all the parts at Summit and it came tuned which to me was a big deal.

I haven't driven it yet but it sure sounds nasty.
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