Ok, rebuilt the carb on my 78 F150 that I just bought and only drove about 1/4 mile home to my garage. Was told it wouldn't idle until it got warm, but I never saw that. I rebuilt the carb using a napa rebuild kit and it's doing the same thing. It starts fine, but won't idle.

If I'm turning the idle screw clowckwise, am I bringing the idle up or down? I put on a new fuel filter and have tried adjusting the fuel mixture screws from 2 turns out to 3/4 in and had no luck. I do remember that they had the fuel mixture screws out several turns and that is why I got the new fuel filter.

When I first put the carb back on, do I need to sit there with my foot on the gas peddle until it warms up to start making adjustments? I see this in a lot of directions, but not sure if I can make adjustments before that or not?

 

For the curb idle screw - turning it clockwise pushes the throttle open, hence raises the idle. If you just play with it you can hear the effect. The more you turn the screw in, the faster the engine turns because the plates are opening more.

For the idle mixture screws - turn them both in until they bottom out (gently), then back them out 1.5 to 2 turns. That is the ball park. If your carb needs the screws out more than 2 or 2.5 turns to idle, you most likely have a vacuum leak. The mixture screws don't have anything to do with the fuel filter. Having them way out just means your idle will be rich. They just control how rich\lean the mixture flowing through the idle circuit is. There are four main circuits to any carb - idle, acceleration, cruising and wide open throttle. Each method has its own way of fuel metering and for idle, the screws are how you adjust it.

Not sure what you mean by keeping the pedal down until it warms up. Yes, to set the curb idle and mixture, the engine should be warmed up, because those mechanisms are for a hot engine. When the motor is cold, the choke and the fast idle cam control the idle and mixture.

 

as soon as I take my foot off the pedal it dies, even if I try to give it gas as it's dying, it still still die. I have to pump the crap out of the gas pedal for it to fire up and keep my foot down on the pedal when I turn the key. It has also started up without me having my foot on the pedal.

I pulled the fuel line off the carb and while it was 'wet' there was no fuel running out of it. I also noticed that when I took the carb apart, the float bowl was dry as a bone. Should fuel be flowing freely out of the fuel line when the engine isn't running?

fmc400, thanks for confirming the idle screw rotation!!

 

When you pull the fuel line off the carburetor, sometimes it will gush a little fuel out, but it won't keep flowing because it loses pressure quickly. The line before the pump, however, has quite a bit of negative pressure - if you pull that line off it will keep siphoning out. However, the post-pump line won't have much pressure with the engine off.

When you took the carb apart and the fuel bowl was really dry - how much time had passed since the engine had been running? Was it right after you shut the truck off?

 

no, it had been a while, so you are probably right, that is why it was dry. I checked the pump out tonight and when I cranked it for 2 seconds, a few tablespoons came out, so think that is ok. But.......I did get it running today, and by running I mean when I pumped the gas pedal twice then turned the key it would start, but would immediately die if I didn't continue to give it gas. I checked the fast idle cam and that was set right (on V) then I adjusted the choke (turned it both lean and rich) and it didn't seem to matter. I even sat there giving it gas until it warmed up to normal temp and it continued to die on me. I even had the wife hold down the gas pedal while I adjusted the idle and looked for a vacuum leak.

Big question I have now is about the fumes/gases I'm getting off the truck. I noticed this when I first brought it home and the smell is so bad that I had to leave the garage. I would describe it as too rich, but the idle mixture screws are only 1 turn out, so I'm thinking that I have an exhaust leak somewhere that is also causing the engine to stall.

I'm not really sure what I need to plug on the vacuum lines when I'm adjusting the carb, so maybe I'm not capping something off properly. I have the carb connected properly and only the vent off the valve cover that goes to the air cleaner and the smaller hose that goes from the tree at the back of the engine (no egr valve to be found) to the top of the air cleaner are plugged. Is there someplace that I should be looking for a vacuum leak that I'm not seeing yet?

 

forgot to mention that when I checked the fuel pump, noticed that the gas was 'brown', so someone at work suggested that I hook up a hose to the pump from a gas can and see if that solved the smell problem...it sure did! I even got it to idle after it warmed up, but it was very high. Of course I was only using my ear to tell, but it seemed high to me, even after I turned it down till it stalled. I'll hook up the tach (after I figure out how to hook up the sears model that I have, instructions make no sense) tomorrow and play with it some more.

I still can't get it to idle when I first start it, and I'm not sure what hoses need to be capped off when you make the carb adjustments. Any ideas???