I have a 1980 F-150 with a rebuilt 302 and a rebuilt stock 2 barrel carb. When it's cold it will bust off but it will immediately die. Then it takes a long run on the starter to crank it. It has a new fuel pump, new plugs and wires, and new distributor cap and rotor. It is also hard to start even after it warms up. What could the problem be?

 

Sounds like the choke is improperly set - either lean or rich. Have you set the choke?

When the engine is cold pull the air cleaner and open the throttle slightly. The choke should close completely. Does it? Then, when the engine starts the choke should open about 1/4". And, as the engine warms up the choke should open fully. And, when the engine is hot the choke should be open.

Edit: And welcome to FTE. You should go into the User Control Panel and enter your location. And maybe set up a signature to remind us what your truck is so we don't have to ask.

 

The choke is adjusted and is working properly. Thank you, I will do that soon.

 

If the choke is properly adjusted then your air/fuel mix is off, and probably lean. I'm betting you have a vacuum leak. Maybe a connection that wasn't made or a hose that is cracked. Or maybe the base gasket on the carb. You can squirt carb cleaner at suspected leaks and see if the idle speed picks up.

 

I will check all if that again this morning but it shouldn't be a issue. I replaced all the vacuum lines and carburetor gaskets when I rebuilt the motor and I tuned the fuel mixture a couple weeks ago. It idles great and runs great on the highway. It's just hard to start and lacks power when first cranked. I usually have to let it sit and warm up before I drive it, if not ill have to give it a lot of gas to keep if from stalling when I ease off the clutch.

 

I was thinking it might be a timing issue, but wouldn't that make it run rough all the time?

 

Two things. First, in future you should tell us what you've done as you describe a problem. In this case we've gone back and forth several times with me guessing what to do but you've already done that. So we have wasted a lot of time.

Second, retarded timing will give you problems at all times. However, the vacuum advance can overcome a lot of that once the engine is running. So you should check the initial lead, which should be in the 6 - 10 degree BTDC area factory, and maybe as much as 14 optimum.

 

That still sounds like a choke problem. You said you set it, but that doesn't mean it's set right. Are your choke tubes intact and hooked up correctly?

Gary gave you good advice. Go back and actually LOOK at your carburetor choke plate and make sure this is happening. For some reason, I don't think it is.

 

Sorry, I see that now. I have looked at the choke and it is working properly. Everything is connected right. The choke pull off opens it about a quarter of the way and it opens like it should. And the heat tube is connected to the manifold and the choke thermostat. I have checked the fuel mixture and choke, and the timing. I replaced the fuel pump about a week ago because it was letting fuel drain back through it leaving me with a dry float bowl. Before I rebuilt the engine it wasn't having this problem.

 

I will recheck everything to be sure it is set correctly. The timing and fuel mixture I set with a vacuum gauge. I set everything to the highest vacuum I could get.

 

Opening "about a quarter of the way" may be too much just after the engine starts. My '81 factory shop manual does not give the spec's for the vacuum pulldown, meaning the distance that the choke is supposed to open under vacuum, but IIRC it is supposed to be ~1/4", not 1/4 of the way.

Were it me, I'd adjust the opening by one of two ways: On those carbs with an external vacuum line I'd put vacuum to the diaphragm and then bend the linkage to get the choke open 1/4". On those without an external vacuum line I'd collapse the diaphragm with my fingers and adjust the choke opening 1/4" by bending the linkage.

An engine will run, albeit poorly, with too much choke. But it usually won't run with too little choke until it gets warmed up. Err on the side of too much rather than too little.

Edit: Just saw the second response. Sometimes adjusting the idle mix to the absolute highest vacuum gets a too-lean condition for starting well. Many times it is best to find the absolute best idle mix and then open the mixture screws 1/8 to 1/4 turn to get a slightly richer mix.

 

I re adjusted the choke and idle mixture like you said. There was Also a vacuum leak where one of the new caps split, I fixed that. It runs better now but it still has the same starting problem. I pulled the air horn off the carburetor before I started it and the float bowl was about a quarter of the way full. It is starting better when warm now. I'm gonna see what happens when I let it sit for about thirty minutes.

 

I'm concerned about your imprecise statements such as 1/4 of the way off and 1/4 full. Carburetors are very precise devices and need to be adjusted accurately. If you are adjusting the carb with the same accuracy with which you communicate it is not going to work properly. Have you, in fact, set the float level/drop as well as the vacuum pulloff accurately? If so, to what spec's?

 

Actually turned out to be an ignition coil problem. Thank you for your help.

 

Glad you got it fixed. Apparently it was giving a very weak spark. Should have thought of that.