Miles per gallon

[FuzzFace2]

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]

Gary Lewis wrote

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]

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

[BigBrother-84]

When offering my own Dad a drink, he always answers "we are never not thirsty".
BigBro seems to fully agree...

[Gary Lewis]

[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.

[FuzzFace2]

85lebaront2 wrote

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]

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]

85lebaront2 wrote

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]

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.

[rcarlisle]

Just to contribute, my 81 with 302 and M5OD-R2 gets 9 - 11 mpg.   No tag on the rear end and the tag on trans was painted over so I have no idea the ratios of either.   But it seems like a lower overall ratio.  1st is almost too low and short - like a granny gear and 2nd gear starts are a bit more slipping.   Seems like it could have higher rear gears to improve the mileage.   It will easily run up to 75 mph.   At that point the steering gets too imprecise to be really comfortable, but I know 75 is solid and easily attainable with more left in it.   235/75-15s for tires.  I haven't counted the wheel revolutions to driveshaft or anything like that.   These first 8 months have been getting it more comfortable and safe.   Truck has been as reliable as an anvil so far.  knock on wood.  

A tach is on the "to do" list soon.   Might help me know a little better.  

I'm also hoping to find a good Ford tuner locally as well.  To get everything set as best possible.  I need a "carb whisperer".   I can tinker and experiment, but I'd prefer to have a good tuner lay magic fingers on it.  

[85lebaront2]

Too bad you're down there, I used to own a carburetor and ignition shop. BTW, that gas mileage puts you in the 460 range. 12.5 mpg at 70-75 mph with a 6400 lb F350 Dually.

[rcarlisle]

Yep.   Something isn't right or wasn't considered when the trans was swapped in.   But I know how people around here think - "Hey let's put a 5 speed in it.   That'll be great.  My cousin has one that will fit".

I wish I honestly knew more of the history of the truck. PO said it was a farm truck.  Not sure that holds water, but who knows.   I have receipts for what the PO did and it did not include the trans.   Just everything forward of trans.  

It's great fun to drive.  Probably has smoky burn out potential, but I can't afford to break it to find out.  But it will get up and go when asked to.  At the expense of gas mileage.  It's longest trips so far are about 15 miles to the cruise in and daughter's house. Might do better on highway for longer trips.

[85lebaront2]

Randy, I would look at the distributor, vacuum advance and mechanical advance in particular. A bad vacuum advance will kill gas mileage as will a sticking ar flat out stuck mechanical advance mechanism.

[rcarlisle]

Good ideas.   It has a cheap chinese dist so probably do need to confirm it's working correctly.   Truck runs well though.  Just bad mileage.

[85lebaront2]

You have one of those Chinese Chevy distributors? Trash can is the best place for it. I personally would go back to a breaker point system before I would touch one of them.

Mechanical advance on GM distributors is under the rotor and is easy to check by removing the cap. with the cap off, grab the rotor and turn it counterclockwise, it should turn with some spring tension and return when released. Vacuum advance can be checked with a vacuum pump, or with the engine running fast enough to have vacuum at the hose, connecting and disconnecting it should bring a noticeable rpm change.

[rcarlisle]

It's not a coil in cap HEI.   Looks like a regular old distributor from the outside.   When I bought truck the #3 tower on cap was cracked on both sides and about to fall out, but the truck was running on all 8 like it should.   SO I located the cap on line and replaced it.  No difference except I don't have to worry about the cap falling apart.  Looks like a cap off an old ford except the terminals are male instead of female.  

I'm going to leave it alone as it is working properly - I want to check the advance operation as recommended above.  But no point in changing something that's working.   The duraspark box is still on the fender but not plugged.  Have no idea if it works or not.

https://swperformanceparts.com/product/r2r6702bl/

[Rusty_S85]

Rembrant wrote

Rusty_S85 wrote

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.

That is my hope, I would be happy with 20 highway even.  I know my '78 Mercury with a 351W would average 26 highway at 75 mph and it while having a smaller front end height wise, still had the brick like front end.  Once I get my build finish I will be doing some logging of economy and seeing what kind of economy I am averaging.  I know for me the roller cam I have for my build is for a 2,400 - 3,000 rpm cruise range and with the axle ratio I am looking at it would put 65 - 75 with in this 2,400 - 3,000 rpm range so here in Texas I should be able to drive just about any highway in the cam`s sweet spot.  The gears I am looking at should put me at 81 mph at 3,000 rpm and 65 at 2,450 rpm

[66gtk]

My all stock '83 with original exhaust and all original unrebuilt powertrain gets about 12-14 mixed city/highway (mostly hwy) with the AC off.  302, AOD, 3.55:1, SWB, EEC-3 all stock and all plumbed/intact original.  NOTE: This is on non oxygenated fuel and tires inflated properly with no little to no load.

[Gary Lewis]

Where's the picture I saw in the email?  I like the deux chevaux in the background.  But your truck is beautiful!