Hello, new here, excited to see if this helps.

6 months ago I bought a 1966 f250 with a 300 in it. It had a new distributor but otherwise hadn't been touched in a while I gathered. After putting a new exhaust system in it ran like a champ with no problems. One day I was driving down the road when it began to sputter and lunge like it was running out of fuel. It died and so I added a can thinking that is what happened. It started right up and acted like all was well then died again, and again, and again. It would catch and run well for a few seconds then lose power and lug until it died. In all that starting and dying 2 things happened. I burned out the solenoid and had a single backfire that ripped open my new muffler.

What I have done to date:
I thought perhaps I had pulled something off the bottom of the tank so changed the fuel filter and rebuilt the single barrel fomoco carb. I then changed the plugs just to do it. It hasn't ran since the day it died. It starts then immediately the carb floods and kills it. And it floods badly. Gas spills out of everywhere it can. I have taken the carb apart a dozen times and messed with float (even pinning it to the floor so no fuel should come in) and it doesn't help. I have taken the needle out and cleaned it and the seat (my carb year doesn't have a seat assembly) but it doesn't help. If I pinch the fuel line I can get it to run somewhat. I have been worried that I rebuilt the carb wrong and maybe that is the cause but local mechanic help is tough to get.

I am doing my best to learn all I can but it is slow going to find answers, so any suggestions would be a great help. Thanks!

 

First thing i would do is check the fuel pressure coming from the fuel pump. An inexpensive gauge(0-15 lbs) and a couple fittings are required to do this. Something may have happened inside the pump causing too much pressure. Seen it happen a couple times.
5 lbs or so of pressure is fine.
Also make sure the float isn't leaking and filling up with fuel. Lastly pull the dipstick and smell the oil. If it smells like gas, change it.

 

Thank you. I wondered if it could be the pump but everyone I've asked said it is highly unlikely that it could fail and push too hard. The pump is old and I want to replace it anyway. I'll let you know

 

Do you live where its hot? Do you get excessive pressure when you take your gas cap off?

 

Hi, here is an update. I replaced the fuel pump and no luck, still spilling fuel out of both seals. I took the carb apart again, turned it over and let gravity hold the float against the needle. Blowing through the fuel line the needle seemed to work fine; no air was getting through until I lifted the float off the needle.

 

Hi rusbukt. I live in Boise Idaho and it does get hot, but we are just getting there. It wasn't hot when the problem started and I don't get pressure when removing the gas cap.

 

check for a plugged return line

 

I'm sure you set the float level when you had the carb apart.? When carb is turned upside down float should lay level with carb body.
Is the float your using brass or black plastic?
Is the float new? Brass floats can become "water logged".
Black plastic floats have been known to absorb fuel also.

 

Thanks hotstuff. This will complete my level of ignorance. What is the "return line"?

 

I did set the float level but have moved it all over the place trying to stop the fuel from coming in. I'll set it again. It is a brass float and doesn't have a leak

 

Did you resolve your problem? I have a similar issue with newly rebuilt carb on 66 F100 352 V8. I do have a lot of pressure when I remove the fuel cap.

 

Update: it ended up being a bad condenser for the reason it wouldn't run, but the carb is still flooding out of everything and everywhere. I can't figure it out. Could it be a faulty heat riser in the manifold?

 

This is killing me because it's a 300 i6; I'm told it doesn't get easier and I just can't seem to crack the case.

 

Have you tried a different carb? Maybe you're tightening the screws too tight and mashing the gaskets or cracked the carb? I'm not familiar with the FoMoCo carbs to know much about their components.

 

Maybe it's time for s new carb? Carbs don't last forever even with rebuild kits. We don't have return lines in our F-100's, not until the later smog years.

Get another carb to try, Good luck...