I've noticed that the new tailpipe that I put on the truck is now covered in black soot, after less than a month. From what I understand, that's a sign of an overly rich condition. Since I've replaced the air filter, I guess the next step would be to adjust the richness on the carburetor. Here's where I run out of experience: on my truck, are the richness adjusting screws the ones on the rear of the carb, with black caps on them? If not, where are the adjusting screws? How do I go about adjusting richness?
Any help would be greatly appreciated.

'81 Flareside
300/6
4 spd
3.31 gears
31" tires

 

I would check the choke first. If it is not releasing properly you will have an over rich condition.
1977 F-100
300 I-6 / C-4 (soon to be AOD)
Offy intake w/Edelbrock 500CFM
Hooker Ceramic coated headers w/duals
MSD6
Whiter whites/Brighter brights

 

I'd pull a couple of plugs too, just to see what they look like

 

baitboy:

The air mixture screw is on passenger side of carb right near the base of carb. Turn it in (clockwise) to lean out the mixture and the opposite to richen the mixture.

At a warm idle, turn the screw clockwise until the engine starts to loose rpms...you are at this point leaning out the mixture, adding more air than fuel. Turn the screw a half a turn at a time to let the adjustment catch up with the engine idle. The ideal setting is to have the smoothest idle without going too rich. Once you lean out the carb, slowly start to turn the screw back out to richen it up, only to the point of higher rpms and smoothness. If you go too rich the idle will start to drop again.

You can also use a vacuum gage to do this by watching the needle's steadiness and its peak reading. A tachometer will give you the same results by trying to obtain the highest rpms. I use my "ear" for rpms and my "feel" smoothness.

The screws on the back of carb are:
1. Choke idle (screw closest to firewall)
2. Curb idle or engine idle (screw closest to carb)
Leave them alone for now, they have nothing to do with the air mixture adjustment that you asked about.

Yes, check to make sure that the butterfly flap in carb is straight up and down on a warmed up engine. If it's at an angle then your choke is too tight or binding up....try cleaning the whole carb down with some gumout carb spray...linkage and all, use an old toothbrush if needed.

good luck, let us know what you find.


1981 F-150 2WD STYLESIDE P/U
4.9L 1 BBL CARB
C6 AUTO
2.73:1 LIMITED SLIP REAR AXLE
STABILIZER BARS FRONT & REAR
6100 LB GVWR PACKAGE
ORIGINAL OWNER
195,700 PLUS MILES
100% STOCK & UNREBUILT
BUILT FORD TOUGH!!!

 

 

I've looked all over the passenger side of the carb, and don't see anything resembling an adjustment screw. Is it possibly on the back of the carb? (The sun wasn't totally up in Seattle, so maybe I missed it.)

'81 Flareside
300/6
4 spd
3.31 gears
33"/31" tires

 

baitboy:

If you have the factory carb like i do, it will be on the lower passenger front side of carb right near the base. It is NOT in the rear of carb. There may be a black plastic limiter cap on the screw head. The screw will also have a spring on it like what you see in an ink pen. If my digital webcam had a long enough cord on it i would take a picture of my carb and show you.

Let me know if you find it....It is there!!!

1981 F-150 2WD STYLESIDE P/U
4.9L 1 BBL CARB
C6 AUTO
2.73:1 LIMITED SLIP REAR AXLE
STABILIZER BARS FRONT & REAR
6100 LB GVWR PACKAGE
ORIGINAL OWNER
195,700 PLUS MILES
100% STOCK & UNREBUILT
BUILT FORD TOUGH!!!