I have a 72 F100 with a 360 and a C6 tranny. I can't seem to get the fuel mix to lean out. The only way it will run is too rich. While setting at a stop light I see blue smoke. No smoke going down the road. Hesitates breifly at take off. Do I need to rebuild the carb? If so, where can I get new idle adustment screws that go in the front. It is a 2 barrel, motorcraft carb.

 

Do you still have your manual fuel pump? Or have you converted to electric...you are definitely getting too much fuel which is causing the cylinders to wash and burn oil. One thing to check in your carb is the floats..if there are holes they will sink and the carb never stops feeding gas.

 

Yea, Ford4Life is right. If its the original carb, it should just have one float in the front (it seems like its the original since its a 2 barrel motorcraft). To me, that does sound like a float issue, most any parts store has floats, such as NAPA or carquest. The hard part is adjusting it, there are tools you can get to more easily adjust it but they arent sold at NAPA or CarQuest because "carburetors are dying out" according to an employee i spoke with. So I would suggest checking the float and a rebuild never hurts and usually you can get a rebuild kit for around 30-50 dollars. I rebuilt my 2 barrel carb on my 1971 ford f250 360 engine and i had no prior experience and i did it by myself. So its not to difficult, just if you run into any issues, come back to this site and don't be afraid to ask questions and if it requires it, post pictures.

 

I have the original Chilton's repair and tune up manual that gives instructions on how to check the float and bowl level. Is that info good?

 

that should be accurate..to check the float just pull it out and dip it in a bowl of gas...if it bubble when you stick it in or when you pull it out you can hear gas inside of it then you need a new one. but for the bowl level the book should help you out. if not there is this place or all the knowledge you need at the click of a mouse.

 

Will a float problem cause the engine to idle irratically?

 

when you say that do you mean it will dump down and pop back up again (in terms of RPMs)?

 

Not really...the float is a static part...the setting remains the same as long as the float mechanism is all there and is seated correctly. However, a sticky needle valve or dirty needle valve seat can starve the carb for gas or cause it to flood over. So can dirty/clogged air bleeds. If you have to do a rebuild, don't be intimidated...it's not that hard to do...be sure to get the kit specific to your carb make and model.

 

I didn't even think about that stuff...you should probably do a rebuild with that many possibilities for problems.

 

No. Just the opposite. It idles fine for a few seconds then goes up for a second or two and comes back down.

 

OK. I did the carb rebuild. I have GREAT acceleration. Idle is constantly up and down as well as at a steady speed. The choke is now either stuck open or closed. No in between. Help?

 

Did you get your float setting right...according to the rebuild kit instructions? Did you replace the idle mixture needles or are you using the old ones? After you rebuild a carb you have to put the basic adjustments back to baseline/stock settings. First, make sure your choke plate is fully open...do that and then look on the left side of your carb...if you have an automatic/electric choke, make sure the fast idle screw below/behind the choke mechanism is set so that the bottom of the screw just touches the cam on the throttle plate linkage...if it's turned in too far, it will keep the throttle plate from closing all the way. Next, turn your idle mixture screws all the way in (clockwise) until they stop (don't crank them down tight, turn them gently until they stop), then back both of them back out about 2 full turns (counterclockwise). Next, reset the curb idle screw, on the right, rear of the carb...turn it counterclockwise until it doesn't touch the throttle plate stop underneath it...work the throttle arm and make sure it is moving freely...now turn the curb idle screw in (clockwise) until it contacts the throttle arm stop...watch the throttle arm and turn the screw in about 1.5 turns clockwise...you'll see the throttle arm move a little when doing this...you want to find the spot where the throttle arm just starts to move and then go 1.5 turns with the screw. After you do all this you will have your carb back to baseline settings.
Start the engine and let it warm up. Does your idle stay constant? It should if the timing and point-gap are set correctly and you have no vacuum leaks. Check your vacuum lines to make sure all the hoses and connections are good. A vacuum leak can make the idle surge up and down, so make sure all of your vacuum lines are there and are hooked up right and tight. Make sure the carb is snugged down tight to the manifold, but don't go crazy and overtighten the nuts...you can crack/break the base of the carb doing that.
You may have to adjust the curb idle screw in a little more to get the engine to idle on it's own. That's how you set the idle speed. Your truck should idle around 650 rpm in Park after the engine warms up, and around 550 rpm in Drive.
Run a check on your setup now...using the info I've posted and post back and let us know how it goes.