Miles per gallon

[FuzzFace2]

With my new engine, replacing my excessive slippage C6 for a aftermarket C6 and switching over to a 3.25:1 axle ratio I hope to be in the area of 18 mpg city and 24 mpg highway.

Rusty, I wish you all the luck in the world, but I have a hard time imagining a 302 running 3000 RPM with a C6 and 31" tires hitting 24 mpg.

Even if you consider the 1987-1996 trucks, with speed density or later on MAF, with 5spd's and 3.08 gears, most of those trucks could barely even hit 20mpg on the highway. They surely wouldn't do in 4th gear at 1:1 ratio like a C6. I can see the Holley Sniper being better technology...sort of...but it's still throttle body EFI, and not multiport EFI.

To throw my old truck into the MPG mix for the OP, it was an '84 2wd Flareside with a mild built 302, a 1991 M5OD 5spd trans, and original 3.08 rear diff. No AC, and no other options really. Truck weighed 3500 lbs. I drove it on the highway quite a bit, and the best I ever got with it was around 18.5mpg...maybe it kissed 19mpg one time, but I'm not sure...my memory is getting fuzzy.

That was at around 2000 RPM in OD, running between 60-65 mph. My AFR was usually a little over 14:1 when I was cruising easily. I did try some highway trips at faster speeds and higher RPM's, and depending on the day it never really hurt my mpg too much...sometimes 1 or 2mpg less, but I think the wind drag negated any efficiency I might have gained with the higher RPM's.

I never did try running the truck up in the 2500-3000 RPM range in 4th gear on the highway to see if the MPG would improve. Maybe that's the answer to getting better mileage...higher RPM's and lower gears...I've never thought to try it.

81 F100 4x2 300 (smog removed & EFI exh manifolds stock pipes to rear) /BW T18 w/2.75 rear gear 235 / 75R / 15 tires.

It would be combo of high way 65 - 70 MPH & back roads 45 - 55 MPH as I would take the high way to work early mornings (no traffic) and the back roads home little less crazys on the road.

I was getting 14 MPG most of the time, hit 15 MPG once or twice but dont know how I did it?

I also dont think I had the AC working at the time.

81 F100 flare side 4x2 300 (smog removed & EFI exh manifolds stock pipes to rear)/NP435 and Advance Adapter over drive w/2.75 rear gear 235 / 75R / 15 tires.

Same roads to from work and get the same MPG but have used AC more with this set up.

I do think it gets better MPG on the high way if I could do 65 with the over drive but I stand more of getting run over even at 3am in the morning.

What I did find is the truck was built when the speed limit max was 55 MPH.

In 4th gear the RPM is 1800. In over drive it is 1400 PRM.

At 70 MPH 4th the RPM is 2500 in over drive it is 1800 RPM.

At 65 MPH 4th 2250 RPM / over drive 1700 RPM

I also have a AFR gauge and it is running a little rich on the high way at mid 13's AFR

I need to open the carb up and lean it out a little more as 1 of the PO really messed up the carb.

It just runs so good I hate to open it and not have it run as good.

I also have more MPG readings to enter in to my log I have been keeping since I got the truck on the road but I cant see the MPG changing all that much from the others I have taken.

One thing I have seen posted in Dave's? MPG post was the added under bumper air damn or spoiler as it cuts down the air running under the truck. One day I will look harder on getting something that will work.

Dave ----

ps: my 02 Dodge Durango 5.9, auto OD, 3.92 gears the best I have ever gotten was 17 on the high way @ 65 MPH.

On the same roads as my 81 F100 I get 14 - 15 MPG also with AC on.

Dave ----

[BigBrother-84]

Dad said his truck [...] always got 10, or 10, and sometimes 10.

Looool! That explains lot of things!

Yesterday, I had a short trip with BigBro (about 40km, 25 miles) and was surprised how fast the fuel level dropped. It's been two years I didn't drive it and, I admit, I forgot how much he is thirsty.

In fact, I was almost suspecting a hole in the gas tank...

Reading at you folks, I simply realize that BigBro runs smoothly and is just drinking "normally".

[Gary Lewis]

Dad said his truck [...] always got 10, or 10, and sometimes 10.

Looool! That explains lot of things!

Yesterday, I had a short trip with BigBro (about 40km, 25 miles) and was surprised how fast the fuel level dropped. It's been two years I didn't drive it and, I admit, I forgot how much he is thirsty.

In fact, I was almost suspecting a hole in the gas tank...

Reading at you folks, I simply realize that BigBro runs smoothly and is just drinking "normally".

Your 351W should do better than Dad's 351M, but not "good". These trucks have a drinking habit.

[BigBrother-84]

81 F100 4x2 300 (smog removed & EFI exh manifolds stock pipes to rear) /BW T18 w/2.75 rear gear 235 / 75R / 15 tires.

It would be combo of high way 65 - 70 MPH & back roads 45 - 55 MPH as I would take the high way to work early mornings (no traffic) and the back roads home little less crazys on the road.

I was getting 14 MPG most of the time, hit 15 MPG once or twice but dont know how I did it?

I also dont think I had the AC working at the time.

81 F100 flare side 4x2 300 (smog removed & EFI exh manifolds stock pipes to rear)/NP435 and Advance Adapter over drive w/2.75 rear gear 235 / 75R / 15 tires.

Same roads to from work and get the same MPG but have used AC more with this set up.

I do think it gets better MPG on the high way if I could do 65 with the over drive but I stand more of getting run over even at 3am in the morning.

What I did find is the truck was built when the speed limit max was 55 MPH.

In 4th gear the RPM is 1800. In over drive it is 1400 PRM.

At 70 MPH 4th the RPM is 2500 in over drive it is 1800 RPM.

At 65 MPH 4th 2250 RPM / over drive 1700 RPM

I also have a AFR gauge and it is running a little rich on the high way at mid 13's AFR

I need to open the carb up and lean it out a little more as 1 of the PO really messed up the carb.

It just runs so good I hate to open it and not have it run as good.

I also have more MPG readings to enter in to my log I have been keeping since I got the truck on the road but I cant see the MPG changing all that much from the others I have taken.

One thing I have seen posted in Dave's? MPG post was the added under bumper air damn or spoiler as it cuts down the air running under the truck. One day I will look harder on getting something that will work.

Dave ----

ps: my 02 Dodge Durango 5.9, auto OD, 3.92 gears the best I have ever gotten was 17 on the high way @ 65 MPH.

On the same roads as my 81 F100 I get 14 - 15 MPG also with AC on.

Dave ----

When offering my own Dad a drink, he always answers "we are never not thirsty".

BigBro seems to fully agree...

[Gary Lewis]

When offering my own Dad a drink, he always answers "we are never not thirsty".

BigBro seems to fully agree...

[85lebaront2]

81 F100 4x2 300 (smog removed & EFI exh manifolds stock pipes to rear) /BW T18 w/2.75 rear gear 235 / 75R / 15 tires.

It would be combo of high way 65 - 70 MPH & back roads 45 - 55 MPH as I would take the high way to work early mornings (no traffic) and the back roads home little less crazys on the road.

I was getting 14 MPG most of the time, hit 15 MPG once or twice but dont know how I did it?

I also dont think I had the AC working at the time.

81 F100 flare side 4x2 300 (smog removed & EFI exh manifolds stock pipes to rear)/NP435 and Advance Adapter over drive w/2.75 rear gear 235 / 75R / 15 tires.

Same roads to from work and get the same MPG but have used AC more with this set up.

I do think it gets better MPG on the high way if I could do 65 with the over drive but I stand more of getting run over even at 3am in the morning.

What I did find is the truck was built when the speed limit max was 55 MPH.

In 4th gear the RPM is 1800. In over drive it is 1400 PRM.

At 70 MPH 4th the RPM is 2500 in over drive it is 1800 RPM.

At 65 MPH 4th 2250 RPM / over drive 1700 RPM

I also have a AFR gauge and it is running a little rich on the high way at mid 13's AFR

I need to open the carb up and lean it out a little more as 1 of the PO really messed up the carb.

It just runs so good I hate to open it and not have it run as good.

I also have more MPG readings to enter in to my log I have been keeping since I got the truck on the road but I cant see the MPG changing all that much from the others I have taken.

One thing I have seen posted in Dave's? MPG post was the added under bumper air damn or spoiler as it cuts down the air running under the truck. One day I will look harder on getting something that will work.

Dave ----

ps: my 02 Dodge Durango 5.9, auto OD, 3.92 gears the best I have ever gotten was 17 on the high way @ 65 MPH.

On the same roads as my 81 F100 I get 14 - 15 MPG also with AC on.

Dave ----

Dave, on your Carter YFA carb (unless you have gone to something else) under the air cleaner gasket you will see a small aluminum flat plug. If you remove that, under it is the adjustment screw for the metering rod. Counterclockwise (unscrewing it) will lean the cruise mixture, clockwise enriches it. There is no need to open one of these up unless you are changing the jet or metering rod.

[FuzzFace2]

Dave, on your Carter YFA carb (unless you have gone to something else) under the air cleaner gasket you will see a small aluminum flat plug. If you remove that, under it is the adjustment screw for the metering rod. Counterclockwise (unscrewing it) will lean the cruise mixture, clockwise enriches it. There is no need to open one of these up unless you are changing the jet or metering rod.

I will have to take a closer look as I dont remember anything that would be near the rod adjustment screw but then again I was not looking.Would that be it to the left of the air filter cross bar screw?

I was also given a 2 or 3 parts carbs and I can check them before I pull the filter to see if mine has it.

I do have to pull the filter anyway to move the 2 temp sensors so the hoses reach for the snorkel flap to hopefully work.

I have been adjusting the vacuum advance can to stop pinging and today I seen the AFR up in the high 14's to low 15's, it has been low 14's high 13's.

Thanks

Dave ----

[85lebaront2]

Dave, on your Carter YFA carb (unless you have gone to something else) under the air cleaner gasket you will see a small aluminum flat plug. If you remove that, under it is the adjustment screw for the metering rod. Counterclockwise (unscrewing it) will lean the cruise mixture, clockwise enriches it. There is no need to open one of these up unless you are changing the jet or metering rod.

I will have to take a closer look as I dont remember anything that would be near the rod adjustment screw but then again I was not looking.Would that be it to the left of the air filter cross bar screw?

I was also given a 2 or 3 parts carbs and I can check them before I pull the filter to see if mine has it.

I do have to pull the filter anyway to move the 2 temp sensors so the hoses reach for the snorkel flap to hopefully work.

I have been adjusting the vacuum advance can to stop pinging and today I seen the AFR up in the high 14's to low 15's, it has been low 14's high 13's.

Thanks

Dave ----

To the right front of the air cleaner cross bar there is a roughly 1/4" aluminum plug, it is a disc plug rather than a cylindrical plug.

[FuzzFace2]

To the right front of the air cleaner cross bar there is a roughly 1/4" aluminum plug, it is a disc plug rather than a cylindrical plug.

I did see that one but thought it was over to far to hit the screw head.

Is there an easy way to remove that plug and then install it again?

Being a disc I guess knock in 1 side so it cocks over and grab it with something?

Thanks

Dave ----

[85lebaront2]

To the right front of the air cleaner cross bar there is a roughly 1/4" aluminum plug, it is a disc plug rather than a cylindrical plug.

I did see that one but thought it was over to far to hit the screw head.

Is there an easy way to remove that plug and then install it again?

Being a disc I guess knock in 1 side so it cocks over and grab it with something?

Thanks

Dave ----

Dave, it may be the one on the left unless that's a screw hole. I haven't had one of those in front of me for a number of years. The adjustment screw is on the metering rod hanger and sits against the pump link that slides in the float bowl casting.

The way the system works was a design Carter used on a number of carburetors, one two and four barrels. The YFA has a dual side diaphragm, bottom side is connected to manifold vacuum which pulls it down to lower the metering rod, the top side is the accelerator pump. The large diameter spring is the one that sets the vacuum level at which the metering rod will pull down, the small spring is the accelerator pump spring and once the vacuum has pulled the diaphragm down acts as a stop. The small plate on top of the pump link with the adjusting screw is the mixture control, loosen the screw and when the diaphragm is pulled down the metering rod sits lower into the jet, tighten the screw and the rod sits higher in the jet.

To remove the plug, a small punch will push it down to the point it is removable. The air cleaner gasket will cover the hole so you can test drive the truck. Once you get the mixture where you want it, turn the plug over so the dent is up and tap it flat to seal it in place.