Basic Info
Year- 1973
Model- F-100
2wd/4wd- 2WD
Engine- 390 6.4
Transmission- C6

So I bought truck and had some fuel problems... Started off taking carb off and doing a full tear down and rebuild. All was ok except for when I put a load on it say, going up hill for a long duration. at which point it "in fires" ( what I was told it was called when pop comes from engine). I took it to a mechanic and he said i was running way lean. I have been searching as to what the proper setting is for idle mixture screws should be set to. What the vaccum reading should be and what the main RPM's should read around. I have found the book from edelbrock website but, nothing really on what is "optimal" for the truck.
I dont think I need to change the jets or metering rods on them as it was running fine before no "in firing" but was gummed up and old nasty gas tank.

Any Thoughts?
Thanks for the help

Adam.

 

Adam

I dont think your "infires" are because of your idle/air mixture screws. There are 3 basic functions of a carb, idle, main metering and power. To answer your fuel mixture question, connect a vacuun guage, and turn in, then back out the mixture screws until you observe the highest vacuum reading. If you dont have a vacuum guage, the highest idle rpm is close, then after achieving the highest rpm obtained, turn the mixture screw in a quarter of turn. Also, I have to assume you built the carb correctly since we are not there, then look for a vacuum leak around the carb base, intake gasket, leaking vacuum hoses, etc. This will cause a lean mixture for the main metering portion. IE, above idle and going down the road without accelerating. If when you "punch it" and it bog's, check your accelerator pump. This is sorta easy. When you pump the throtle linkage while the engine is off, you should see a steady stream of fuel squirting down both primary barrels. Also, check your fuel pressure to the carb. This is important, some have to use a fuel regulator, even with a factory mechanical pump. Did you adjust your float level's properly? Is the fuel filter dirty? Lack of fuel and or fuel pressure can cause your issue as well.

Believe it or not, by your description, it seems under load you need more fuel, and the carb is starving, which points to a a fuel restiction, like a plugged fuel filter.

 

Mine are about 1-3/4 turn out .... but idle screws don't have an affect on mid range running as you're doing on long upgrades. Vacumm at idle under no load if near stock cam I'ld expect near 20 inches. Aggressive cam shafts lower it usually. Not sure what you mean by "main rpms" but my 351M idles at about 850.

Did you set float levels?

Isee that it has an Edelbrock carb, does it have a fuel pressure regulator on the fuel line just prior to the carb and if so, is it by chance Mr Gasket or Spectra? If either one, it's restricting fuel delivery. I put a brand new one on and set it, it idled OK but under load .... popping and carrying on dreadfully lean as it was running out of gas. Didn't make it 1/4 mile from the house. Limp home and ordered a Holley 12-803 and that one works very well!

If it has NO regulator, it should as the std mech fuel pump likely pumps 7 psi or it should .... and these carbs are unlike Holleys, they do not like more than 6 psi max, it's recommended to set a regulator to 5.5 psi. (a Holley will tolerate as much as 8 psi)

I'm assuming you got the springs back in with the step up pistons that control the metering rods?

 

OK... I got this figured out. Thank you guys so much. Tomorrow is a fun day full of more truck work.

 

Let us know what you find. If nothing else, someone (me) will learn something...again...

 

Do you have the fuel pressure regulator on it yet? Edelbrocks have to have a FPR on them to work properly.

 

Well, according to the edelbrock owners manual i'm running lean. but according to carter i'm running fine. Went out today and adjusted floats seems to be running better. Cant say for sure as the hill im having problems with i haven't gone over it yet. going to try changing a/f mix tomorrow and get all dialed in. if im still having problems from there i figure i will replace metering rods and jets with whats suggested for "optimal stock performance". Will keep it updated as to what goes down tomorrow.

 

If you arent running the FPR, you will have this very same problem, ad infinitum...

 

What is the idle suppose to be for A 1976 F-150 AWD with a 360, stock carb, Auto trans (c4)?

Please help

 

All adjustments
Warm,
In neutral: 800rpm
in gear: 600-650rpm
Cold
start about 1000rpm to start with step downs on high idle cam.

 

Thank you very much

 

One more thing. What are the adjustments for the 2 screws on the front of the carb.? I seem to be running a little rich and can not find this information anywhere. The Carb model number is D5TE-ASA an autolite 2100