300 1bbl carb boils over.

[green68250]

Hey guys,
I just bought a 1970 F-100 with a 300 and a 4-speed. The carburetor idles fine but once I drive it the fuel boils over and hydrolocks the motor. Any ideas? I have been through that carb 6 or 7 times and it was a rebuilt to begin with. I found some gummed up teflon in the needle seat but that still didn't fix the problem. I was told the motor was from the early 80's buy a guy at work. It has emmision ports that are plugged in the head. They PO put the new carb on it am a new fuel pump. Could the fuel pump be the wrong one? Its the type with the canister with a filter in it. That is the correct filter for a 1970 300 but not an early 80's 300. So if anyone has any ideas that would be great, I could sure use the help!

Thanks a lot,

Corbin

[69timemachine]

What brand of carb are you running? I got a reman Carter YF for my '69 240 and had a somewhat similar problem out of the box. It ran fine all the time, but when the carburetor approached normal operating temperature, fuel would start POURING down the accelerator pump rod and onto the scalding hot intake manifold. I opened up the top on it and the old carb and noticed that the top gasket on the old carb had a hole for what appears to be a vent or equalizer passage. It was located between the throttle bore and the bowl. The new gasket did not have that hole, so I added it with my hole punch. I reassembled it and so far, it hasn't happened again. I guess the rebuilder just didn't notice that the gasket didn't have that hole. Might be something worth checking into on yours.

[green68250]

Hey 69timemachine,

Thanks for the tip. I believe the carb is a carter. I will check the gasket for that hole. I dont have an old carb to look at but I will see if I find anything obvious. When you say the vent are you talking about the thing that sticks out over the venturi just looks like a tube? What you describe is exactly what mine is doing and I have heard that these carbs are know for doing that. Thanks again for the tip, ill let ya know if it worked.

Thanks,
Corbin

[green68250]

I looked at my gasket and it looked like it had all of the holes it needed. I know the float is set right and that there isn't anything in the needle seat. It can idle all day long but once I drive it for about 15 min. straight she starts to boild over. Any other ideas?

Thanks again,

Corbin

[69timemachine]

No, the hole in the gasket wasn't for the main vent tube that you're talking about. It was to connect the bowl to a small passage in the top cover. Not totally sure what that little passage is for, but I assumed it was sume kind of vent or equalizer. It was roughly in the middle of the "wall" between the bowl and the throttle bore. The reason I knew to check it was because I saw an indention on the bowl half and a passage hole on the upper half, but the gasket was sealing them off. Then I saw that the old gasket had that hole to connect them, not block them off. It seemed like a reasonable conclusion to add that hole to the gasket, and sure enough, it worked on mine. Yours boils over into the throttle bore though and not down the accelerator pump rod, right? If it's overflowing out of that little vent tube over the throttle bore, then that's usually the float hung open or the float needle not sealing off. Man, you got a real headscratcher there!

[green68250]

No its leaking down the accelerator pump like yours was. When I checked the gasket there was one spot in roughly the same location you describe where the gasket had an indentation on it. I looked for a passage between the top cover and the main part of the carb but it didn't look like there was a passage between the two that would require a hole in the gasket. It was like a vent from the bowl to the throttle bores through the main wall but not up into the top cover. I suppose I could put a hole in the gasket there and see what happens. It should have any affect on the sealing. Yes this is a real head scratcher!

Thanks again,

Corbin

[69timemachine]

Yeah, you might give that a try. I don't think it would cause any harm. I used one of my gasket hole punches, but you could use an X-Acto knife or razor blade. Let me know how it turns out. Good luck!

[cdherman]

The accellerator pump in a carter YF is in the bowl, so I cannot see how fuel could be leaking down it on the outside. You sure you have a Carter YF?

Cause an Autolite 1100/1101 does have side mounted accell pumps.

If its boiling the gas out (and not just leaking) then you also need to check the exhaust riser. In the exhaust manifold there is a flapper that has a bimetalic coil on the outside. Its *supposed* to open when cold and shut when hot. Supplied heat to the base of the intake manifold to prevent carb icing.

BUT -- if that flapper stays open, the base of the intake gets gawd awful hot and will boil out the carb in nothing flat....

Remaned carbs are mostly crap. Buy a kit for the carb you have and rebuild it yourself. You have a better change getting it to run that way than plunking down $150 for a spray painted junk carb from Autozone.....

[green68250]

My leak is out of the bottom of the bowl through the meetering rod/"pump lifter link" according to my chiltons. Its the rod underneath the bowl on the front of the carb. I will definately check out that heat riser and see what I find. Do you think that wouldn't supply enough heat to boil the fuel untill I drive it a distance? It will idle all day long and not boil over untill i drive it. Thanks agiain for the idea I bet thats probably what it is.


Corbin

[69timemachine]

Yes, that's exactly where mine was leaking from. It's the flat steel link that passes up into the bowl and pulls down on the accelerator pump plunger inside. I checked my exhaust riser valve in the manifold too and it moved freely and opened & shut as it should. Then I noticed the missing hole in the gasket, added it, and the problem went away in mine after that. But like I said, mine is for a '69 model. I don't know if later versions would have that little passage that needs the hole in the gasket.

[green68250]

Well I finished the water pump and thermostat housing today and got her running again. I let her idle for a good 20 min and checked to see that the exhaust valve was working, which it was. Then I drove it up and down the street a few times all without shutting it off. Drove it back to the house shut it off let it sit a minute while I decided if I should drive it to the gas station or not. I decided to drive it and made it there and back without an issue and let it idle in the driveway once I got back for another 15 min and still nothing. I'm not convinced its fixed untill I drive it a longer distance. So if the gasket doesn't need a hole in it and the exhaust valve is working correctly, what else is there to check? I didn't really do anything to make it run other than adjust the fuel mixture screw a little and get the choke to work.

Thanks again,

Corbin