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Username Post: Fuel consumption        (Topic#362590)
Hards..60 
"2nd Year" Silver Supporting Member
Posts: 595
Hards..60
Loc: Northern Ontario,Canada
Reg: 10-20-07
09-15-20 07:35 PM - Post#2803545    

Folks, have any of you experienced something like this. I've been driving my car now since last summer....here and there.

I think I have put about 600 miles or so on it to date. And now for some reason lost the gas mileage. I'm guessing I'm down to about 10 miles to the gallon since I burnt about a quarter of a tank in just over thirty miles the last time I took it out.

I used to be able to travel about 200 hundred miles on half a tank...now I'm down to 60 miles.

The center carb was rebuilt along with the other two. I have no vacuum leaks, it starts real good, idles properly. Vacuum gauge shows 20+ inches hg, timing is a little advanced to 6 degrees, plugs are looking good, gap is bang on at 35 thou, accelerator pump works no changes when in gear car does not stall, no hesitation, no smoke.

I don't get it....did something break inside the carburetor or something? Fuel pump?

I'd appreciate any ideas or thoughts....I'm lost!!!

Thanks guys.

Roger.

1960 Impala 2dr hard top - 348 tri















 


DonSSDD 
Silver Supporting Member
Posts: 7392
DonSSDD
Loc: Nova Scotia, Canada
Reg: 08-21-01
09-16-20 03:30 AM - Post#2803552    
    In response to Hards..60

Big difference in city and highway mpg, in city you are using 3 carbs more often? Would that explain it?

63 Pontiac Parisienne Sport Coupe(CDN Chev mechanically (409, 4 speed),62 Bel Air SC (sold), 59 El Camino (sold), 62 Bel Air SC(sold), 63 SWC Vette (sold),
Member #2194


 
Hards..60 
"2nd Year" Silver Supporting Member
Posts: 595
Hards..60
Loc: Northern Ontario,Canada
Reg: 10-20-07
09-16-20 06:10 AM - Post#2803562    
    In response to DonSSDD

Hi Don
No this is all highway driving with the two secondary carburetors not operating.

When I had all three carbs set the thing ran really well. It shocked me actually to what it could do in comparison to how it ran before I made changes.

Just to be clear, I had the 348 rebuilt and replaced the power glide with a 200-4r and when I made those changes it was like I bought a new car.

It just for no apparent reason dropped off on the gas mileage and short of removing and disassembling the carburetor I can't figure out what is going on.

I could understand dirt causing problems, stalling, losing horse power, hesitation, but this, I don't know......maybe it's not fuel..

Roger.

1960 Impala 2dr hard top - 348 tri















 
Jens 
"12th Year Silver Supporting Member" & 58-60 Subject Matter Expert
Posts: 7234
Jens
Loc: Iowa.
Reg: 04-21-02
09-16-20 10:09 AM - Post#2803586    
    In response to Hards..60

Are you using an ethanol blended fuel if so that could be some of it. I checked mine once going to goodguys in Des Moines on the interstate. With 3.08s and a trailer on back it only got 10. I blamed it on smiles per gallons and the Carter WCFB.
348s weren’t always the best on gas. My 327 Q jet gets 18.



 
Original58 
Contributor
Posts: 552
Original58
Loc: Manitoba, Canada
Reg: 10-30-13
09-16-20 05:01 PM - Post#2803612    
    In response to Jens

Is your oil over full?
Sometimes the fuel pump can leak from a pinhole in the diaphram

Jeff

1958 Biscayne 283 Turbo-Glide 31,000 mi (now 35,000 and counting) driven daily
1966 Mustang Inline 6- C4 57,000 mi and growing daily
1929 Graham - Paige 612- the eternal headache that I will never sell


 
acardon 
Ultra Senior Member
Posts: 11418
acardon
Loc: DFW TEXAS
Reg: 03-25-05
09-16-20 07:06 PM - Post#2803618    
    In response to Hards..60

  • Quote:
I'm guessing I'm down to about 10 miles to the gallon since I burnt about a quarter of a tank in just over thirty miles the last time I took it out.



Have you checked it from a full tank or just using the gauge? The tank sender could be corroded causing the gauge to be off.



Don
66 Corvair (driving)
57 2dr HT (driving)
56 2dr HT (waiting to be restored)


 
vet65b 
"10th Year" Gold Supporting Member
Posts: 652
vet65b
Loc: Albuquerque, NM
Reg: 02-09-06
09-16-20 07:07 PM - Post#2803619    
    In response to Hards..60

Roger,
For that drastic a drop in mileage I would start looking for a leak between the tank and the fuel pump. The wonderful fuel we use may have attacked one of your rubber hoses, or the tank may be leaking. Good luck. Bill

Bill Wilhelm
1965 Impala SS
1966 Corvette, ordered for my 23rd. birthday


 
JayChicago 
"10th Year" Silver Supporting Member
Posts: 418
JayChicago
Loc: Chicago
Reg: 01-03-13
09-16-20 09:08 PM - Post#2803622    
    In response to vet65b

My thoughts go along with acardon’s post above. Maybe just hasn’t been driven enough yet to get accurate measurements of fuel consumed over a longer time frame? The fuel gage and tank float are not precision instruments and may act erratic from time to time.



 
DonSSDD 
Silver Supporting Member
Posts: 7392
DonSSDD
Loc: Nova Scotia, Canada
Reg: 08-21-01
09-17-20 02:20 AM - Post#2803628    
    In response to JayChicago

Rogers’s car is a new restoration so all the fuel lines would be new. If he has a fuel leak, he should be able to smell it?

A 348 tripower and fuel economy are not usually mentioned in the same sentence.

In my daily driver, I used to keep my fuel economy numbers religiously, I have records for over 700,000 kms. To know your true fuel economy, you really need to manually record your miles and fuel volumes and do so over a bunch of tanks of gas and average them out. When you fill up, you may not be topping up the same each time, you may have done more idling in some tanks or had a higher % of city driving. Each tank of gas will vary widely for mileage numbers and you need to measure fuel economy averaged over several tanks, say at least 1,000 miles.

Most of us don’t drive our cars enough to get a really accurate fuel economy number, we don’t always drive them to achieve good fuel economy either.

My 409 burns a lot of fuel, I rarely drive it long distances on the highway. My speedometer is not accurate so my measurements would need adjusting and guessing, and I keep my revs up when driving to keep my fuel system unclogged. I’d be scared to get a real fuel economy number. I get maybe 200 miles on a tank.

I have a diesel for long runs, I can bragg about how good it is on fuel, but I am having a whole different experience driving the 63 and fuel economy doesn’t affect my enjoyment. Sorta like calculating the cost per pound of the fish you catch while operating a boat?

I guess what I’m saying Roger is that there may be nothing wrong with your fuel economy? If something is wrong, it should show up as the car not running smoothly, putting out clouds of black smoke, stalling, stumbling, hard to start when hot, etc.

Don

63 Pontiac Parisienne Sport Coupe(CDN Chev mechanically (409, 4 speed),62 Bel Air SC (sold), 59 El Camino (sold), 62 Bel Air SC(sold), 63 SWC Vette (sold),
Member #2194


Edited by DonSSDD on 09-17-20 02:24 AM. Reason for edit: No reason given.

 
japete92 
"6th Year" Silver Supporting Member
Posts: 1488
japete92
Loc: No. Virginia
Reg: 01-18-13
09-17-20 06:04 AM - Post#2803635    
    In response to vet65b

  • vet65b Said:
Roger,
For that drastic a drop in mileage I would start looking for a leak between the tank and the fuel pump. The wonderful fuel we use may have attacked one of your rubber hoses, or the tank may be leaking. Good luck. Bill



A leak seems the most logical to me.

It MAY (emphasis on MAY) be leaking only at peak fuel pump pressure (driving down the road). Under those circumstances, one may not notice the smell.

Just a theory.

Pete




 
Maxbigblock 
Valued Contributor
Posts: 2879
Maxbigblock
Age: 69
Loc: Stuart, Florida
Reg: 12-16-01
09-17-20 07:37 AM - Post#2803646    
    In response to Hards..60


All the running gear seems to be in tip top shape. Is your car ever parked some place where someone could be siphoning a few gallons from time to time? Its a rare occurrence now with newer cars that all have a screen in the tank filler neck. I hope this isn't the case but it would explain a little fuel loss.

Max

I'm originally from the ONCE great city of Flint, Michigan. The birthplace of General Motors, where A C Spark Plug was formed and headquartered, where the first Corvettes were hand built, and where my 1955 Chevy was made.



 
mahlmann 
"10th Year" Gold Supporting Member
Posts: 1785
mahlmann
Age: 76
Loc: Las Cruces, NM
Reg: 01-20-11
09-17-20 10:05 AM - Post#2803661    
    In response to Maxbigblock

I would tend to expect the fuel pump may be the culprit. Be sure you are not bleeding fuel onto your crankcase. My fuel pumps tend to last less than 2 years on our current fuel mix. Our factory stock 348 with 3X2 carbs gets about 14 mpg on highway cruises as long as I don't open up the other two carbs very much. Once, on a 5.5 mile parade loop through and around Sunnyvale, CA driving behind a marching band, we got 1 MPG!



Mike Ahlmann
Las Cruces, NM
'50 Tin Woodies (two) Ramon and Willard
'58 Impala Sport Coupe
'69 El Camino SS-396
'07 Ford F150 to haul parts for above
'16 Ford Explorer 3.5 EcoBoost - Red Rocket


 
Hards..60 
"2nd Year" Silver Supporting Member
Posts: 595
Hards..60
Loc: Northern Ontario,Canada
Reg: 10-20-07
09-17-20 05:27 PM - Post#2803689    
    In response to mahlmann

All very plausible causes and I very much appreciate the great ideas.

Today, with the hood opened and me staring at the engine and asking it "what's wrong with you?" I had a wild idea. Took the car out and did the same as I did before, 30 mile drive on full tank and the needle barely moved in fact it only moved about the width of the needle itself....maybe a little more.

The difference today, was that I took off the air filter and drove the car without it and voila!! or eureka!!

I thought I was losing it there for a moment because this car had good gas mileage when I first took it out last year while using the power glide....this summer I have a 200-4r....I gave the car a couple more gears.

Even though this filter looks clean, it sucked. I took a light to it and shines through nicely....it must be quality...don't know.

I'd like to get myself an original style breather rather then use the filters I have now, but those who sell them want the price of a car for them. So for now I guess I'm going to have to try and find good quality air filters until I find a breather assembly on sale.... :crazy :

Thanks folks....really appreciate the ideas.

Attachment: HPIM1554.JPG (1.7 MB) 3 View(s)




Roger.

1960 Impala 2dr hard top - 348 tri















 
DonSSDD 
Silver Supporting Member
Posts: 7392
DonSSDD
Loc: Nova Scotia, Canada
Reg: 08-21-01
09-17-20 06:01 PM - Post#2803693    
    In response to Hards..60

Roger, the gauge is not that accurate for measuring fuel economy IMHO, you need to do the numbers over a bunch of fill ups.

63 Pontiac Parisienne Sport Coupe(CDN Chev mechanically (409, 4 speed),62 Bel Air SC (sold), 59 El Camino (sold), 62 Bel Air SC(sold), 63 SWC Vette (sold),
Member #2194


 
PLS 
"8th Year" Silver Supporting Member
Posts: 1576
PLS
Loc: Smyrna, Georgia
Reg: 06-07-12
09-17-20 08:08 PM - Post#2803707    
    In response to Hards..60

I have no clue what a 3x2 setup air filter housing looks like or the air filter but this is what I am using for 1x2 setup. I am getting probably around 10 to 12 mpg.

A video of that beauty on the road would be great for us out here in CT land trying to picture what it looks and sounds like Roger

Very easy to upload to youtube. Lamar

Attachment: IMG_0410.JPG (83.79 KB) 4 View(s)




Attachment: IMG_0409.JPG (73.86 KB) 3 View(s)






 
Hards..60 
"2nd Year" Silver Supporting Member
Posts: 595
Hards..60
Loc: Northern Ontario,Canada
Reg: 10-20-07
09-18-20 06:19 AM - Post#2803727    
    In response to PLS

A video of that beauty on the road would be great for us out here in CT land trying to picture what it looks and sounds like Roger

Very easy to upload to youtube. Lamar




I like that idea Lamar....let me work on that.

Roger.

1960 Impala 2dr hard top - 348 tri















 
Hards..60 
"2nd Year" Silver Supporting Member
Posts: 595
Hards..60
Loc: Northern Ontario,Canada
Reg: 10-20-07
09-18-20 06:31 AM - Post#2803728    
    In response to DonSSDD

I agree, Don.

It's not the best way to measure mileage. If I were looking for an exact I'd need a measured amount of gas for that and a particular driving condition also.

What I'm getting at is I've noticed a difference in consumption by the gauge with a full tank and driving the same distance that was better than that which I was experiencing a few days ago.

As mentioned a 348 and fuel economy do not normally appear in the same sentence....to me though this seemed like quite the change.

Please let me have this one....


Roger.

1960 Impala 2dr hard top - 348 tri















 
DonSSDD 
Silver Supporting Member
Posts: 7392
DonSSDD
Loc: Nova Scotia, Canada
Reg: 08-21-01
09-18-20 07:59 AM - Post#2803733    
    In response to Hards..60

Just trying to reduce your stress Roger, no need to have a stroke over a bit of extra gas in a car with 3 carbs?

63 Pontiac Parisienne Sport Coupe(CDN Chev mechanically (409, 4 speed),62 Bel Air SC (sold), 59 El Camino (sold), 62 Bel Air SC(sold), 63 SWC Vette (sold),
Member #2194


 
PLS 
"8th Year" Silver Supporting Member
Posts: 1576
PLS
Loc: Smyrna, Georgia
Reg: 06-07-12
09-18-20 09:07 AM - Post#2803740    
    In response to Hards..60

Roger, if this old man can do it "anyone can"

As far as gas mileage goes, I have no idea why I still calculate it on a trip but I still do.

I heard it said years ago that if you had to know how many mpg the vehicle that you were looking to buy got then you probably couldn't afford it.

According to my mileage, if I had two more carburetors I would only get maybe 6 mpg. but the fun that I get driving it around makes it worth it.



Edited by PLS on 09-18-20 09:13 AM. Reason for edit: No reason given.

 


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