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350 getting 5mpg


Crom Cruach

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10 minutes ago, stangeba said:

All this milage talk had me wondering what my 71 stock 350 4 BBL has been averaging.

I have a spreadsheet with all my vehicles miles and gas station fill up data since 2006. 

Here is what my Monte has averaged each year with a total average of 16.17 M.P.G. mostly regular 87 unleaded gas.

  16.17
      YEAR  MPG
2006 15.5
2007 16.4
2008 16.1
2009 15.4
2010 16.2
2011 16.5
2012 17.0
2013 16.4
2014 15.7
2015 15.9
2016 16.0
2017 15.6
2018 16.9
2019 16.5
2020 16.4
2021 16.2
2022 16.2

 

 

Damn Bruce, you're more anal-retentive than me. LOL

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I like it! I record every gas station visit with mileage, volume, and cost. It’s how I check how much fuel is left, until I replace the fuel sender and get my gas gauge working. 

black smoke is only on starting the engine cold, so the choke is fully engaged obviously. I actually wear a mask until I get it out of the garage! Once warm there is no smoke and she sounds great. 

It will stay on fast idle until I blip the throttle, is that normal?

So I re-adjusted the idle mix, the idle revs, then dropped the advance back to 11°. Total got up to 30 at just under 4000 revs, happy with that. I’m guessing the mystery 3-way connector in my last post was a vacuum leak. Drives lovely, but need to get her to a pump when I have time to check mpg again. 

Snowball alert: is this coolant coming out of this hose? My new moroso rad cap is great (cheers Scott!) but now the pressure releases elsewhere! Should this not just come out the overflow? I did have the engine running for half an hour without driving…

 

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For me, keeping track of milage is my way of detecting problems…

My 350 gets an almost constant 16 local driving...… If it drops to 14 it's usually because I'm putting my foot in it.. When she drops to 12 , I start sniffing out the problem… When I leave California on a road trip, I'll get 18 to 20….  

I believe this California gas is half air bubbles  (oxygenated) and when it settles a day or so after a fill up, I'd swear I'm about two gallons shy in the tank. … My Gas gauge is deadly predictable, so it's not the gauge…. I keep a few gallons of seasoned gas on my property for equipment etc, and often top off the Monte… When I do this,, there is no change of gauge level …. 

As far as gauge accuracy is concerned,, the gauge has always erred on the side of stupidity by not letting me run out of gas… It always has a reserve after first showing empty … (about 3 gallons )  

Ed C…  

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@Crom Cruach I read that your black smoke is only on startup. I would still check the float level, condition of the float, and make sure there is no debris in the carburetor. These are prime reasons for poor fuel economy. External adjustments such as the air mixture screws are not going to have that significant of an impact on fuel economy.

Also, you mentioned a vacuum leak. Did you fix that? A vacuum leak will cause poor fuel economy as well.

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Stupid question, but have you checked to see if your odometer and speedometer are reading correctly? Mine was reading .9 miles for every full mile traveled until I replaced the plastic gear that drives the speedo. If you have a gps app on your phone you can quickly see if the miles are reading correctly just to be sure the trouble is in the engine at all. 

 

Like I said, stupid question but......... 5 mpg is very low indeed. 

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Hi Paul, That's not a good sign at that heater hose. I'd replace those hoses Pronto! Just remember to cut the hose Length ways at the heater core if you can.Then, while replacing, Just a touch of White lithium grease on ends, you'll be happy with that. As for your carb problem ,I'm leaning towards a bad fuel float myself, if there is too much fuel in the bowl, it will leak out into throttle body,(sometimes you can see it i carb while idling). I'd see if it's a brass or foam style float and replace with correct one. Carb kit isn't that expensive, just the time to fix it. Worked on these for years, best mpg I got out of one? 23mpg, 1977 Monte Carlo.... what a tank, but a beautiful ride!

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@Crom Cruach Taking the top off of a Quadrajet isn't difficult. There are two screws inside the primary (front/small) throttle bores that are easy to miss; look down past the choke plate and you will see them. Otherwise, it's pretty straight forward.

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Paul,   Just need to drain from petcock at bottom of radiator is all.That will get you down to water pump level. You can get to float from top.just be careful not to drop anything in throttle bores. Bottom butterflies should always be backed off throttle screw for this feat! If you replace top gasket,make sure you match up new gasket. You can lose a hole, and it will run like crap.

Edited by 420ponies
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Runnin Quadrajet on mine. Had to rebuild it 7 years ago... runs great.. no complaints with the quad... someone behind me in Bristol last year said it smelled a little rich.. and it was.. toned that back a bit , it’s doin good... all kinds of books available on rebuilding and tuning different quadrajet carbs...

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5 minutes ago, Searsman said:

Runnin Quadrajet on mine. Had to rebuild it 7 years ago... runs great.. no complaints with the quad... someone behind me in Bristol last year said it smelled a little rich.. and it was.. toned that back a bit , it’s doin good... all kinds of books available on rebuilding and tuning different quadrajet carbs...

Although I might add , experience is better than a book!. A book is just a tool . 

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On 6/10/2022 at 5:29 PM, Crom Cruach said:

I like it! I record every gas station visit with mileage, volume, and cost. It’s how I check how much fuel is left, until I replace the fuel sender and get my gas gauge working. 

black smoke is only on starting the engine cold, so the choke is fully engaged obviously. I actually wear a mask until I get it out of the garage! Once warm there is no smoke and she sounds great. 

It will stay on fast idle until I blip the throttle, is that normal?

So I re-adjusted the idle mix, the idle revs, then dropped the advance back to 11°. Total got up to 30 at just under 4000 revs, happy with that. I’m guessing the mystery 3-way connector in my last post was a vacuum leak. Drives lovely, but need to get her to a pump when I have time to check mpg again. 

Snowball alert: is this coolant coming out of this hose? My new moroso rad cap is great (cheers Scott!) but now the pressure releases elsewhere! Should this not just come out the overflow? I did have the engine running for half an hour without driving…

 

Time to cut the end of the hose off and re attach it... Or just get a new hose.

 

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On 6/10/2022 at 6:52 PM, stangeba said:

All this milage talk had me wondering what my 71 stock 350 4 BBL has been averaging.

I have a spreadsheet with all my vehicles miles and gas station fill up data since 2006. 

Here is what my Monte has averaged each year with a total average of 16.17 M.P.G. mostly regular 87 unleaded gas.

  16.17
      YEAR  MPG
2006 15.5
2007 16.4
2008 16.1
2009 15.4
2010 16.2
2011 16.5
2012 17.0
2013 16.4
2014 15.7
2015 15.9
2016 16.0
2017 15.6
2018 16.9
2019 16.5
2020 16.4
2021 16.2
2022 16.2

 

 

Ya I couldn’t do that. It seems that I only drive the cars to the gas station. I fill the cars up with the good stuff and siphon it all summer long for the lawn equipment. I get about 10 miles to a tank of gas. Lol. 

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Anyone remember the story where someone was adding gasoline to their friends vehicle each day. The friend started bragging how great his fuel economy was. Then he changed something silly (like a sticker on the window) and then the friend started to remove gasoline from the tank and it freaked the owner out how this sticker could lower his fuel economy. 🤣

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I took my 71 out of storage last October. I don’t remember if I’ve ever checked the mileage since putting the 402 in it in the late 80’s. I’ve only put about 24,000 miles on it since then. I filled it up back in October and filled it up again today on the way to a cruise in and checked the mileage. This is the result. (402 with turbo 400, 3:31 gears, 2700 rpm stall torque converter) 

976F93EB-930D-49BD-BB08-8470F5AF4198.jpeg

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On 6/11/2022 at 8:30 PM, 420ponies said:

Bottom butterflies should always be backed off throttle screw for this feat!

James If I knew what this meant I definitely would have done it!

I took the air horn off and replaced the float and needle, and set up the float height as best I could to around 3 / 16ths. Maybe more like 7 / 32nds. new gasket, cleaned the air horn with carb cleaner, reassembled and now I'm not getting any fuel in the bowl. It's kind of bubbling on the outside. see video. can anyone chime in on what I might have done wrong here?  

 

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Looks to me , you don't have any fuel in bowl. I pour fuel into tube coming up in center of carb. Straight spark plug boot works well. Pour some in and press accelerator pump.  That's the arm moving up and down in video. Pump could also be pinched, check plunger. That should then squirt into throttle blades.

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Update: 12 miles per gallon this morning on a 23 mile drive on hilly roads! Very pleased with myself, thanks for all the help guys.

Also, the drive was out to a new mechanic, who had a corvette, 'stang, and loads of classic euro cars like Alfa Romeos and of course lots of beemers. He's going to line the radiator and replace the water pump for me, and do the suspension stuff. Making real progress. 

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