Carburetor Selection
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New User
Joined: Jun 1999
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Carburetor Selection
I have a 1970 F100 with a 390 and a 4bbl carburetor. The carb that is on it now is an Edelbrock 750. This seems a little much for the motor but it was given to me by a freind so I put it on. I do tow a boat once in a while but most of the time it is just regular street driving. I get about 8mpg which I would like to improve on. Does anyone have any suggestions for a different carb that would give me better gas mileage and maybe more power. Any suggestions would be appreciated.
Elder User
Joined: Oct 1999
Posts: 917
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From: Kelseyville USA
Carburetor Selection
You may be over carburated..
Iam running a 1406 edlebrock carb and manifold...
390 FE Let me know what carb # you have and maby I can help you further!!
__JOHN__Õ¿ö
72 F-250
Iam running a 1406 edlebrock carb and manifold...
390 FE Let me know what carb # you have and maby I can help you further!!
__JOHN__Õ¿ö
72 F-250
Fleet Owner
Joined: Jun 1999
Posts: 24,552
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From: Creedmoor, North Carolina
Carburetor Selection
FN, you carb is too big a 600 cfm is plenty large. What kind od milage were you getting before, you installed it. I am being more convinced that the two barrel might be better. The FEs don't starve for gas with them.
What size rears are you running and is it a 2X4 or 4X4.
John
66 F100s
In the still cool hours of the night, you can hear chevys rusting away.
What size rears are you running and is it a 2X4 or 4X4.
John
66 F100s
In the still cool hours of the night, you can hear chevys rusting away.
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New User
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Carburetor Selection
I had a Holley 650 in the truck before I replaced it with the 750 and got about 11 mpg. The truck is a 2x4 but I really do not know what gears I am running in the rear. (How would I find that out?)
I have been contemplating putting a 2 bbl back on the truck but did not know the pros and cons of it.
I have been contemplating putting a 2 bbl back on the truck but did not know the pros and cons of it.
Posting Guru
Joined: Jul 1999
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From: Inthepast
Carburetor Selection
Yuo can figure out your gear ratio from the door tag if the rear-end is original. Post the axle code on the tag and the year of your truck. If the rear-end is not original it may be possibly to find a tag on the differential with the id info. If so post that too. There are only two other ways: one is to take the differential apart and look at the numbers on the ring gear; the other is to estimate the ratio by turning the drive shaft and watching a wheel spin. Rear gearing is a ratio between input turns in rleation to the output turning the wheel. For instance, a ratio of 4.56 will require 4.56 turns of the drive shaft to equal 1 turn of the wheel.
<font color="#f80732" size="4" face="Graphite Light">Stock Man
</font><font color="#0000FF" size="2" face="Graphite Light">1967 F-250 FE 390 4wd</font>
<font color="#0000FF" size="2" face="Graphite Light">1966 F-250 I6 240 2wd LWB Flare Side</font>
<a href="http://www.hometown.aol.com/tbeeee">http://www.hometown.aol.com/tbeeee</a>
<font color="#f80732" size="4" face="Graphite Light">Stock Man
</font><font color="#0000FF" size="2" face="Graphite Light">1967 F-250 FE 390 4wd</font>
<font color="#0000FF" size="2" face="Graphite Light">1966 F-250 I6 240 2wd LWB Flare Side</font>
<a href="http://www.hometown.aol.com/tbeeee">http://www.hometown.aol.com/tbeeee</a>
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Fleet Mechanic
Joined: Nov 1999
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From: Lower 48
Carburetor Selection
I had a 390 rebuilt to stock specs once and decided I wanted a 650 holley on it. I had a lot of problems with it, so I switched it out for a stock 2BBL. The mileage, performance, and reliability all increased. No shortage of power whatsoever, that truck could pass annything but a gas station. 11 mpg on the interstate, downhill, with a tailwind - empty or loaded.
As for rear ends - Jack up one rear wheel. Put a chalk mark on the driveshaft. Rotate the rear wheel one complete revolution and count the number of turns the d/s makes. It should get you pretty close. A 3:08 in a 1/2 ton with 235/15's should run out about 2200 rpm, or a 3:73 in a 3/4 ton with 235/16's should do about the same 2200.
Hope this helps
Trail Rider
As for rear ends - Jack up one rear wheel. Put a chalk mark on the driveshaft. Rotate the rear wheel one complete revolution and count the number of turns the d/s makes. It should get you pretty close. A 3:08 in a 1/2 ton with 235/15's should run out about 2200 rpm, or a 3:73 in a 3/4 ton with 235/16's should do about the same 2200.
Hope this helps
Trail Rider
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Carburetor Selection
For the rear gear ratio, I think you turn the wheel twice and count the number of driveshaft turns. If its only once then I have a 1.50 gear ratio and I know thats not right. Also, if you have a tach, run the truck to 60 mph and post rpms and tire size.
Posting Guru
Joined: Jul 1999
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From: Inthepast
Carburetor Selection
As I recall it matters if you have a locking axle and whether or not both wheels are off the ground if it's an open diff. I should probably jack my truck up and try this sometime.
<font color="#f80732" size="4" face="Graphite Light">Stock Man
</font><font color="#0000FF" size="2" face="Graphite Light">1967 F-250 FE 390 4wd</font>
<font color="#0000FF" size="2" face="Graphite Light">1966 F-250 I6 240 2wd LWB Flare Side</font>
<a href="http://www.hometown.aol.com/tbeeee">http://www.hometown.aol.com/tbeeee</a>
<font color="#f80732" size="4" face="Graphite Light">Stock Man
</font><font color="#0000FF" size="2" face="Graphite Light">1967 F-250 FE 390 4wd</font>
<font color="#0000FF" size="2" face="Graphite Light">1966 F-250 I6 240 2wd LWB Flare Side</font>
<a href="http://www.hometown.aol.com/tbeeee">http://www.hometown.aol.com/tbeeee</a>
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
Carburetor Selection
FN, Tis my experence to find behind that engine a 3.25 behine a SD, and 3.00 behind an auto. Not cast in stone, but rises to the top.
John
66 F100s
In the still cool hours of the night, you can hear chevys rusting away.
John
66 F100s
In the still cool hours of the night, you can hear chevys rusting away.
Elder User
Joined: Aug 1999
Posts: 910
Likes: 0
Carburetor Selection
You may also find a tin tag with ID info on the differetial itself although probably really greasy and in need of a lot of cleaning. I have a 9inch in my 76 2wd that originally had a 300/3sp. That tag is on the front passenger side of the "third member". I took the numbers and a wrecking yard ID'ed the numbers as a 31 spline 3.50 gearing. I also have a 69/4sp 2wd that has a Dana rear end. I haven't found the tag but I jacked it up (both wheels off the ground) and marked the driveline and the tire. I discovered that both wheels turn together on this rear end and that there were about 3 1/2 turns of the driveline to one wheel turn. For kicks, I did the same test on the 9inch and it appeared to turn 3 1/2 times as well (3.50). Both wheels definitely didn't turn together on the 9inch. I'm still not sure what the rear in my 69 is and I would be skeptical of a door tag as the door isn't original and there is evidence of a lot of swapping on the truck. How do you ID Dana rearends? There does appear to be a cast number on the upper back edge adjacent to the rear cover.
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Carburetor Selection
Thanks for all the help. I think I am going to try a smaller carb first as I can use some from friends. If that does not work I will probably go back to the 2bbl carb. The only thing I have to do if I do go back to the 2bbl is find a manifold.
Thanks again!
Thanks again!
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