You call this gas mileage?

[Bill Braun]

Well, no. Not that I ever expected to be crowing about the fuel "economy" of my newish '67 big block, but I wondered if there wasn't still something else I was missing (big thanks to Jerry for putting me on the trail of a solution). I've checked the archives and found some cryptic references to the deleterious effects of defective Holley power valves on fuel consumption. I've also read somewhere that properly functioning power valves can be tested by covering the round air tubes, which causes an idling engine to stall. Is this correct?

Is there some other way of assessing this without a full carb rebuild?

I've got no illusions about this, but since I pay about $3.50 a gallon for gas, I'm sure you can all appreciate my interest to stretch it as far as possible.

Bill Braun 33186

[Wayne W.]

Re: You call this gas mileage?

My 67 427-390 gets 15.5 hwy. at most any speed with 336 gears. 16.5 if its raining.

[Jerry Clark]

Re: You call this gas mileage?

Hi Bill:

If you are disillusioned with your gas mileage I'll trade you for a slightly built 69 that will give you a whole new perspective on your poor mileage but you have to pay the shipping. (BTW what the heck does Swiss pizza taste like.

If ya need Holley parts let me know, I don't know how difficult these are to obtain there.

jer

[Bill Braun]

Re: You call this gas mileage?

Jerry,

If it is that '69 tripower beast in the photos you sent me, I may just take you up on that. Can one ever have enough 'Vettes? Still hoping to avoid rebuilding the carb, though. Judging by the prices they charge, the local US car parts store charters the Concorde for shipping.

Swiss pizza is OK, but nothing beats the pizza I used to buy at the South Ferry terminal in Manhattan as a young lad. I'm drooling at the thought. I wonder if it's still there. I'll probably dream about it tonight and wake up just as I'm about to take my first bite.

Bill

[Bill Braun]

Re: You call this gas mileage?

Wayne,

15-17 strikes me as reasonable. Looking at what I'm presently using (around 8), however, it strikes me as the Holy Grail. This car sat unused for a over a year before I bought it and I suppose the carb may be gummed up a bit. This weekend I'll check the float levels and see if I can't figure out another possibility.

Bill Braun 33186

[Jerry Clark]

Re: You call this gas mileage?

Bill:

That's the one, beginning to get the urge to have another mid year anyway. If you haven't any other obvious problems, i.e. ignition, compression or valvetrain you either have a carb problem or you are simply not used to a big block. Remember , I'll send you carb parts however you might be better off to consider buying a Jerry Luck restored correct carburetor, I remember your choke problem, he can supply you with a correctly dated Holley for your 67 at a reasonable price and you can be certain if you are still not satisfied with your mileage it isn't going to be the carbs fault.

jer

[Tom B.]

Re: You call this gas mileage?

I gotta agree with Jerry, Bill. The tri-power I have (and a rear with a 4:11) will guzzle down a 1/4 tank of gas in about 20 minutes out on the highway. I've never been more afraid to check my MPG and probably never will. The high octane leaded fuel I get is at least $3.50 / gallon. TBarr #24014

[Bill Braun]

Guess you're right...

Guys,

I was hoping to find some easy method of being sure the car was running as it should be. It starts easily, idles smoothly, runs well and really accelerates when I want (perhaps I've been 'wanting' a bit too often..). That said, the car is so damn much fun to drive I find myself checking the weather report several times each day. I'd never had a big block before, but I'm getting used to the idea real fast.

Thanks for the advice all the same.

Bill Braun 33186

[Duke W.]

Altitude

Bill:

Pardon me if I misinterpreted, but I got a cue in some previous post that you live in Switzerland. What is the prevailing altitude for your typical driving? Carburetors meter fuel on the basis of volume flow, so as altitude increases carburetors become continuously richer as air density is reduced. If you're at or over 3000 feet reducing jet size will bring fuel flow back into proportion with ambient air density.

Duke

[Bill Braun]

Re: Altitude

Duke,

I'm not in an overly mountainous region (near Basel), and although my wife might disagree, I try to restrict my driving speed to the non-aerial range. I suspect the local elevation is about 800 feet above sea level. Would the carb jetting make a difference at this modest altitude?

I would also like to say that your technical contributions to this Board make excellent reading and reference.

Bill Braun 33186

[Duke W.]

Nope...

The OEM jetting is set up for "average" conditions, and a mere 800 feet elevation is certainly within this range. So it's back to working on the Holley, which is an area outside of my experience envelope.

Thanks for the kind remark.

Duke

[G B.]

Gas $ vs. parts $

Bill -

I doubt your power valve has failed. Usually when this happens you have black smoke and a very rough idle (if it will idle at all).

I think the biggest detriment to your mileage is the "double -pump" Holley you're using. Its mechanical secondaries require an extra accelerator pump to eliminate stumble. It works, but it also makes them a terribly inefficient carburetor.

You may be able to justify a carb change based on $3.50/gallon gasoline. Try a new Quadrajet. They're now made by Weber USA and sold under the Edelbrock name, but they're still available. A new one will set you back about $400 plus shipping. You can probably sell your Holley on eBay for $125. Maybe you can make up the difference over time in gas savings. Iron GM Q-jet intake manifolds are very cheap at US swap meets. It may be more practical for you to shop for one through the Driveline though.

[motorman]

Re: You call this gas mileage?

if your carb is a holley double pumper it is set up for racing and is very rich for steet driving,especially the idle and intermediate circuit. you can install smaller jets and compensate by drilling out the power valve restrictions. if the idle is still too rich you can drill out the idle air bleeds to lean out the idle.