Fuel consumption...no not a tree hugger, just FMI

[Wietse]

Guess the more carbs, the more it drinks

If mine takes 8mpg but it is normal, i am ok with that.
As long as i know i am not burning unneeded fuel because i did not set it up properly for it’s purpose.

 

[moes]

it depends how heavy your foot is too!!!!!!! that will lower your gas mileage. As for an AFR gauge check this ebay listing for a AEM gauge best price you will find!! Get Summit ( price is 237) to match the price and they will, I do it all the time. This is the one I use and recommend to customers and it does not need to be calibrated, you will like it

This is the lowest price you will find!!
https://www.ebay.com/itm/AEM-30-411...ash=item3ce6dec863:g:l3AAAOSwY~1aH5Ki&vxp=mtr

here is Summits listing

https://www.summitracing.com/int/parts/avm-30-4110

 

[metaldad]

68 coronet vert, 440, 727, 3.91, holley 4780, eddy 7193 intake.
9-10 mpg/hiway/top down

 

[Wietse]

Thx Moes, I will order one of them AEM AFR meters from Ebay, some also offer direct payment for import charges as well which makes i easier and clear.
Some shops here in the Netherlands sell this kit for over 300 Euro ($360,-), i can buy almost 2 of them from the US. (You guys are so lucky!)

I checked on my nearest favorite shop for Holley jets, now they mention a size number, say 75 but has a .082" hole.
For sure they done that to keep things simple.
So currently i have size 78 in my primary side, so i could buy a set of 75 and 73 size and play with that once the AFR meter is installed?
Think i will leave the secondary as is, once i feel the extra resistance in the pedal i know the secondary's are coming in and that it's time to check the rear mirror for 5-0 and get a good grip on the steering wheel

 

[747mopar]

4:10 is all you needed to say, you can fine tune it all you want but it will always suck the fuel with 4:10s. When I switched to an overdrive my fuel mileage nearly doubled along with the miles I put on it. I'd try a gear swap, 3:55s are a great gear for a BB.

I'm getting in the neighborhood of 20 mpg out of a 456 stroker.

 

[Wietse]

Very true, and i am planning on changing the rear final drive to 3.55 in the future.
My plan is to remove the whole lot for rebuild, change bearings, rebuild brakes etc. and include a gear ratio swap.

I was reading through about carbs and tuning, now realising i always have been checking manifold pressure on a "Ported Manifold vacuum port"
This port sits on the primary metering block, passenger side, is this wrong or right?
As i understand, here you measure the "vacuum" above the throttle plates instead of below and does not give you the manifold vacuum reading, thats probably why i am reading such low manifold vacuum.

 

[coloradodave]

You can compare the List number (located on the front of the choke air horn) with the included page to see what the stock jetting is on a Holley 750 double pumper. I would start there. And, yes, the vacuum should be checked from a source below the throttle blades. Check it by putting your finger over the nipple with the car idling.
http://www.mortec.com/carbs.htm

 

[Wietse]

My carb is a HP version and has no choke. I never found any list number, but i found it should come standard with 6.5 power valves and 73 jets on both primary and secondary.
With the secondary having a blocked power valve the jets size should be increased, which it has with 84 jets and the secondary works fine.
I am pretty sure it runs very rich on the primary so getting 75 and 73 jets and a AFR meter i should be able to make some improvements there.

First thing i should get a proper vacuum reading!

 

[Wietse]

In the link you send it should be 72,84 jetting and only a single 6.5 power valve.
As per that list it could only be a 80528 or 80529.

 

[miller]

It takes rocket science on setting up carbs...read your spark plugs...and go from there.

 

[Wietse]

I have 3 weeks now to make a plan, and order the required materials like AFR meter and some other sizes jets.
Already have a good strobe for checking timing and a decent vacuum gauge.
First i will check and record everything as it is now, with timing, jets, vacuum, AFR readings and check status of the spark plugs and post here my findings and pictures.
After hopefully you guys can help me out with your knowledge.

 

[Sweet5ltr]

I have 3 weeks now to make a plan, and order the required materials like AFR meter and some other sizes jets.
Already have a good strobe for checking timing and a decent vacuum gauge.
First i will check and record everything as it is now, with timing, jets, vacuum, AFR readings and check status of the spark plugs and post here my findings and pictures.
After hopefully you guys can help me out with your knowledge.

If you plan to purchase an EFI kit in the future, I would continue driving it until then, wouldn't purchase a wideband gauge; that will be $200-$300 that could have been spent toward EFI.

Honest answer, it's just a large displacement engine with an inefficient fuel metering device. On a wideband, you'll see how brutally inefficient a carburetor is at everything but steady cruise (low-speed), idle, and WOT. Every single transition (slight change of throttle input) carburetors fail miserably at, that's a majority of our time driving (you would see this on an AFR gauge). Even the antique EFI setups we run (TBI), engine vacuum and coolant temperature changes the fuel tables drastically. If you've noticed on newer cars, some have no throttle response (drive-by-wire) and I would place a bet it's 100% for economy. On some vehicles, it's fairly dangerous when pulling out in traffic. My SRT in sport/track mode, felt like it made another 30-40 horsepower at the tire, it didn't, all it did was add 'x' % additional throttle input from the driver. So normally, 10% TPS (throttle position) would then be telling the computer 20% TPS (throttle position). It seemed to also remove that delay / hesitation that we all have grown to hate with modern EFI vehicles. With the aftermarket TBI EFI setups, there is absolutely no delay and way better throttle response than even a carburetor (remember, 58psi vs. 6-7.5 psi being sprayed down the intake manifold).

At the end of the day, the more power / displacement / cylinders and engine has, the more fuel it's going to burn. I posted up a YouTube video the other day of a 1997 Viper GTS MPG test - 488ci. MPFI. Overdrive manual transmission. Excellent Aero. 3.07 rear gears. 3,300#. 5.6 MPG city. . . . 18 MPG highway. . .

 

[rlem1977]

4:10 is all you needed to say, you can fine tune it all you want but it will always suck the fuel with 4:10s. When I switched to an overdrive my fuel mileage nearly doubled along with the miles I put on it. I'd try a gear swap, 3:55s are a great gear for a BB.

I'm getting in the neighborhood of 20 mpg out of a 456 stroker.

If you don't mind sharing, which overdrive setup did you go with?

 

[747mopar]

If you don't mind sharing, which overdrive setup did you go with?

I bought a T56 out of a Viper, basically the same tranny you get when you buy a T56 from Summit or one of the other providers only different gearing.

 

[rlem1977]

I bought a T56 out of a Viper, basically the same tranny you get when you buy a T56 from Summit or one of the other providers only different gearing.

Thought maybe you had a 727 and tried Gear Vendors, etc.

 

[747mopar]

Thought maybe you had a 727 and tried Gear Vendors, etc.

I enjoy driving a standard plus there's a lot less that can go wrong with them.

 

[coloradodave]

In the link you send it should be 72,84 jetting and only a single 6.5 power valve.
As per that list it could only be a 80528 or 80529.

So, there is no air-horn (the part that sticks up above the air cleaner sealing surface)? Look on the tops of the metering blocks and also the base plate for the list number.
This may help: https://www.holley.com/support/carburetor/

 

[oldmanmopar]

Your 69 Coronet has a problem. It should consume more fuel if your using it to its full potential. I can definitely help you there. What would be your asking price. LOL

 

[Wietse]

Your 69 Coronet has a problem. It should consume more fuel if your using it to its full potential. I can definitely help you there. What would be your asking price. LOL

I know what you mean, but until the day i am confident with the car that is 100%, mechanical and reliable wise i am being carefull.
There is no way i am selling it!!

 

[Wietse]

As i was reading through a Holley carb manual, describing all settings etc. i read that the 4150 HP carbs comes with replaceable air bleeds.
Not that i was thinking of replacing this or so as i read pretty much all warnings this should be touched by pro's only, which i am not.
But i never noticed on mine these are replaceable so looking at some pictures i have of my carb i notice mine are fixed, looking a but further and noticed my primary intake in rectangle shaped, and not rounded as the HP version.
So i am pretty sure mine is a "normal" 4150 Double pumper and not an HP version.
Guess they cut the air horn off (believe this is done to gain some air flow??), thats why i cannot find a list number...

I've ordered the AEM wide band AFR meter and a set of #75 and #73 jets to play with if needed, depends how it runs with the #78 jets.
My plan is to firstly install the AFR meter, check and record AFR readings at idle, several cruising speeds (road limits) and at high load/WOT.
Check and record initial- and total advance, and get a proper idle vacuum reading.
Then i will look at the spark plugs, and see what they tell me. (currently i have NGK, heat range #5, ordered a set of NGK heat range #6 as well..just in case)
That should give some good basics to pull some conclusions.

I will report back with that and probably we can figure out where are some potentials for improvements, being it spark plugs, jet sizes or timing.
Anything i missed out on? Or other things to consider tracking for reference/changes?