I am having trouble with my idle on an '81 300. Of course when I start the truck it idles rough until it warms up. As soon as I get it out on the road though, it idles really rough when I stop. The thing is stock from top to bottom.

Also, I have been thinking of converting it to a fuel injected system, but I have no idea where to start. Any ideas or articles?

-Any and all help would be greatly appreciated.

 

I'd suspect a vacuum leak. Check vacuum hoses, carb attachement to intake manifold (mine was loose when I had your problem) and the EGR valve (been there twice). Good luck. (Assuming you have eliminated ignition system problems)

Raul
w/ 81 F-100, I6, SROD, Carter 1V non-feedback carb, no A/C, no PS, no PB, but it gets me where I need to go

 

At an engine idle, spray some carb cleaner all around the base of the carb. Listen for any increases in RPM's and smoothness. Do the same around the base of the EGR valve. If something is loose it will suck air and cause a rough idle. The carb cleaner spray will temporarily seal the air leak and the engine will regain its proper idle qualities. Retorque anything that has come loose. Check your PCV and the hose going to it, make sure it is on tight and not all dry rotted. Get some carb cleaner you can pour into the gas tank, you might have a filthy carb inside.

Lastly, you might attempt to adjust the air/fuel mixture screw at the passenger side base of the carb. Turning the screw inward will lean out the mixture, backing it out will richen it up. I use "white out" to put a reference mark on the screw head. Turn the screw quarter turns at a time and let the engine catch up to the adjustments you make, go slowly.

I turn mine in (lean) until the engine starts to stumble, then i back out the screw until the idle speeds up and smooths out...if you go too far out it will start to lose idle quality again.

One last thought.....Check to see if the preheat dooor on the air cleaner snorkle is opening up on a warm engine. If it stays closed after heating up, the carb has to suck hot air off the exhaust manifold flex-pipe that goes to the snorkle. This really restricts the air flow going to the carb and will give you poor mileage and performance. I have disconnected and plugged all the vacuum lines going to the snorkle air temp sensor. My preheat door stays open all the time.

Lets us know what you find, and good luck.


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
190,000 PLUS MILES
100% STOCK & UNREBUILT
BUILT FORD TOUGH!!!

 

I found out what my problem was.....

It seems to be a sticky choke. I just turned the "****" on the back of the carb, and "loosened" the choke.

Does anyone know how to adjust the choke so that it works correctly?

Thanks

-matt

 

There should be 3 small screws on the plastic choke ****. Loosen them so you can freely turn the black plastic **** (choke coil). Remove your air cleaner assembly so you can see the carb butterfly flap.

On a cold engine turn the choke **** until you see the butterfly flap in the carb move. Without being under the hood right now looking at mine i can't say for sure which way will richen or lean it, but you will be able to tell by turning it yourself. It may even have the words RICH and LEAN with arrows showing the direction to turn. Use some white-out or etch a reference mark in the plastic before you start turning. You want the butterfly flap to be closed but not so tight that it would take the heat from a blow torch to open it.

Or....on a totally warmed up engine turn the choke until it just starts to close then back off so that the flap is straight up & down in the carb throat. This method may be easier for you to do. Make sure to snug up the screws after adjusting so your choke setting doesn't slip.

You may need to do this once more if you don't get it just right the first time you do this. But at least you'll know which way to turn it if your choke is off in either direction. That's where the reference mark comes in handy.

Spray some gumout carb cleaner or eqivalant on the linkage around the rear and side of the carb where the choke is. Is your heat tube connected from the exhaust manifold to the choke housing? It's an aluminum tube about the size of a thin straw...it draws heat into the choke coil **** to hasten the amount of time your engine needs to be choked. They tend to rot away over the years.

Choke idle speed is another adjustment. The rear of carb is where the idle speed screws are. Closest screw to the carb is your engine idle speed screw, the one next to it, closer to the firewall is your choke high-idle adjustment. Don't mess with these yet unless they're out of whack.

Keep us updated on your progress. good luck.


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
190,000 PLUS MILES
100% STOCK & UNREBUILT
BUILT FORD TOUGH!!!

 

Thanks for the advice, I just got around to fixing the thing. Your advice worked really well, I had to do it twice, I didn't get it right the first time (when it was cold). It was a little easier for me to do it when it was warm.

Thanks for all your help, maybe I could return the favor sometime.

-Matt

 

 

Hey kaisermat,
i'm glad i was able to help you!

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
193,000 PLUS MILES
100% STOCK & UNREBUILT
BUILT FORD TOUGH!!!