Engine Dies After Startup ?

[Insayn]

So I have a 1976 Bronco with a rebuilt 302 and 2 barrel Motorcraft carb that ran perfectly for years, until the other day. All the work was done by the previous owner. It normally starts fine and idles high until warmed up or I step on the throttle. The other day I started it and put it into gear to back out of the driveway and it died. Tried it numerous times and it dies each time. It has fuel, the tank switch is on the correct tank, checked down the barrel and see fuel squirt when I pump the throttle. If I stay on the throttle slightly it'll continue to run, off the throttle it'll die. I'm not familiar with carbs so I am having a hell of a time. It ran a few days before this just fine as I ran errands. Any help as to what to look for?

 

[DirtDonk]

This is interesting. Didn’t I just see this posted here yesterday? I can’t find it now. Or maybe it was another form somewhere?
I’ll have to check. See if I can copy and paste my list from that reply.

 

[DirtDonk]

Never mind. Different scenario.
I’ll see if I can be of any help for you after rereading your question.

 

[DirtDonk]

The first thing I’m thinking of is a vacuum leak. But it could be a combination of vacuum leak, joke, not adjusted properly, an idle speed, solenoid, failing, or combination of items. When was the last time it was given a tuneup? A lot of things might need to be at this point.

Another scenario that comes to mind is, especially if the vehicle sits for extended periods, the modern fuels may have gummed up the insides of the carburetor slightly.
Sounds like your fuel is getting to the carburetor.
Sounds like your accelerator pump squirter are working.
But it doesn’t sound like the main fuel circuits are working.
Maybe it’s gummed up, or maybe the idle is set too low. Can you post a couple of pictures of the area around the carburetor?
Are you still running the stock Dura Spark electronic ignition

 

[Insayn]

It does sit for several weeks or months without running, but haven't had any issues with it just starting. I drove it 2 weeks ago to run errands and filled it up then. When I went to start it last week it started acting this way. My first thought was the carb dirty or an old, reused part finally failed. It had idled fine before the day I drove it. I'll get my son to snap some pics now.

 

[DirtDonk]

That’ll be great. Thanks.
You can post them to your “garage“ or “gallery“ functions above. If you wanna post them directly to the discussion, you have to be a contributor for $12 a year.
Otherwise, there are free hosting sites that you can link to as well.
The $12 is worth it, but since you just got here and may only have this one question, you have to decide whether it’s worth it or not.

There are additives that you can run during the year to stabilize the fuel, or clean the system once in a while. You may even have gotten some water in your tank from a pump at a gas station.
I found that running cleaner through the system once or twice a year really helps with the overall longevity between fiddling with things.
A little late for that at this stage, but thought I’d add those for a future reference.
The pictures will help to see how your 76 is set up.

 

[Insayn]

 

[Insayn]

 

[Insayn]

I noticed the cap on one of the carb fittings is dry rotted. Not sure what that goes to.

 

[Insayn]

 

[Insayn]

 

[Insayn]

 

[Insayn]

Thanks for pointing me in the right direction DirtDonk. Paying attention to the vacuum ports specifically I noticed rot on one and replaced it. Still heard a sucking sound and found the one in the rear where the end of it was flat out missing. Two new caps and it runs like a too.

 

[DirtDonk]

Fantastic! Yeah, these modern rubber caps are well known sore spot for us. They dry rot very quickly.
Yours could be very old and have lived long life giving good service. But new ones are often bad within a few months. So keep that in mind the next time it starts running a little off.
Definitely vacuum leaks, causing at least some of your issue.

 

[DirtDonk]

The ones at the bottom of the carb were causing most of the trouble. The top one is simply a float bowl vent for emissions.
It should be plumbed into your charcoal canister on the frame. Or, if you have a later model 76, it would have a plastic canister bolted to the passenger side firewall.