Rebuilt carb, engine won't idol

I just rebuilt the carb in my 54 chevy and it won't idol. I have to step on the gas pedal to start it and once it starts it runs ok but dies if I try to let it idol. This is my first time messing with carbs so I have no idea what's going on.

could be a few things - idle adjustment screw not quite right, mix not quite there (seat mix screw then back it out 1.5 turns), vacuum leak, tired fuel pump, float level,...I'm assuming rochester 1 barrel carb for the 1.5 turns. Might try stovebolt.com for folks who know there way around these really well.

The idle adjustment screw is outside near the bottom of the carb correct? How dO I adjust the mixture? I was told that the screw above where the floats are attached needs to be tightened and then backed off 1 or 2 turns but when I did that it seemed to be a little loose. Wonder if that could be one of the problems?

Very first thing to check: I assume it still has points, make sure they are clean and gapped properly. There's a saying among old farts like me: '90% of carburetor problems are actually ignition problems'.

Make sure there are no vacuum leaks. It will never run right if something is leaking. Also if it has mechanical valve lash adjustment, make sure they are properly adjusted. A too tight intake or exhaust valve will drive you nuts trying to 'adjust around it'.

Assuming these are correct: setting idle mixture is first. That's the 'needle' screw with the spring under it. It looks like this:

The same guy has a pretty nice tutorial on rebuilding his carb: http://my54chevy.com/index.html

With the engine off, turn it all the way in until it bottoms, do this by hand! Even screwdrivers will add enough 'torque' to damage the screw tip. Once it's all the way in, back it out 1 3/4 turns, this is your starting point.

Next set the idle speed, this is a screw that the throttle linkage stops against. Again with the engine off, make sure the choke is all the way open, then turn the screw out until it no longer contacts the linkage. Now turn it back in, watching for it to touch the linkage. Once it does, turn it another 2 turns. These are your base settings.

Now start the engine. It may or may not idle well. If it does not idle well, start by turning the idle speed screw (that's the one on the linkage) in until the engine will idle. Now let it warm up completely (thermostat open) before fiddling with the mixture screw.

Once warm, get the idle close to the factory spec (probably 750 RPM) by again turning the idle speed screw. (At this time it's a good idea to check the ignition timing before proceeding). Once you are there, now it's time to fiddle with the mixture screw. Turning it in will lean the mixture, turning it out will richen it.

With the engine idling, turn the screw in 1/4 turn, then wait. It will take a few seconds for the engine to respond. It will either speed up and smooth out, or slow down and get rough. If it slows down and gets rough, turn the screw OUT 1/4 turn till you get where you were, then wait a few seconds and listen. Once the engine steadies, turn the screw OUT another 1/4 turn and listen.

You are looking for the fastest smooth idle. If you walk to the back of the car, you can also listen to the exhaust note to get an idea of where you are. If it's smooth and steady, congrats that's where you need to be. If it's has kind of a high note and has 'splashy' sounding 'sput sputs', it's too lean. If it's got a low rhythmic thumping beat, it's too rich. Fiddle with the mixture screw accordingly

This is trial and error, it takes a few adjustments both ways to get it right. In practice, if the carb float level etc are right you will usually find your mixture adjustment to be somewhere in the 1 1/2 to 2 1/4 turn range. Once the mixture is right, you may find the idle speed is off, turn the idle speed screw either in or out to get the idle speed where it should be and you are done.

That should do it. Of course we are assuming all of the passages have been cleared.

Thanks for all your help. It always helps having a second person to help. Kinda hard to start the truck and make adjustments when it doesn't idle. With my neighbors help we got it running; however we found the problem. The rebuild kit did not come with a mounting gasket and there's a rather large vacuum leak at the base of the carb where it mounts.

ok easy fix. go to store get paper cut gasket and your good.

Ok so I made the gaskets for mounting. Tried starting it and it ran for about 5 - 10 secs. When I restart it same thing. A friend questioned the floats and needle valve. The screw above the float was loose so I tightened it and put everything back together. It started right away and ran for a couple mins. Trying to let it warm up the idle started to drop off until it died. When it died it shot fuel out of the front of governor. Now it won't start and when I stop cranking on it I can hear the fuel shooting out. Is it flooded? Did I miss a gasket during the rebuild?

Sounds like the needle is sticking. Easy way to fix: use the plastic handle of a screwdriver to rap on the carb body in the area of the needle. Don't wail on it, just rap it smartly. It may take 1-2 tries but that usually works. If it doesn't, the top has to come off of the carb for a look-see.

To start a flooded engine: be sure the choke flap is open, use something to hold it open if need be. Hold the throttle to the floor (do NOT pump it!) and engage the starter. It may take 20-30 seconds of grinding away before it will start. In real bad cases, I've pulled the spark plugs, unplugged the battery lead from the coil (don't want random sparks around fuel!), then spun the engine for 20 seconds or so with the throttle held wide open. Let everything air out for 15-20 minutes, then reinstall the plugs, reconnect the coil and try to start.

Ok I'll try that. I probably should double check my float level as well.

My float level was way off. Once I set it, the truck fired right up. I played with the mixture screw and couldn't really notice a difference.