77 f150 351m. The truck starts right up when cold and has no problems while driving but after shutting it off for a little while it floods sometimes but not all the time. I can hold the pedal to the floor and it’ll start up after a few cranks and runs fine. Sometimes it’s flooded after just a few minutes and sometimes it isn’t. It has a knockoff of a motorcraft 2 bbl carb (not sure of brand). Has anyone had this problem? Anyone have any suggestions?

 

Welcome to FTE


How do you know it is flooded?
When it dose start dose it start just like it is flooded till it clears out?
If so it is not the carb but the gas .... this is known as hot restart and there area lot of posts on this in all the truck areas where the motor uses a carb.

Todays fuel is made to vaporize and add heat and it dose it like nothing else.
Your carb is sitting over a heater, on a v8 right in the center!
Motor is up to temp and you stop of gas or a quick run into the store and come out and need to crank, foot to floor and it will then start, Again theis is normal with todays fuel.

You need to keep the carb as cool as you can.
Some have a heating plate below the carb sending coolant thru it.
Remove this heater by bypassing the heater hoses but leave the plate.

Overs use a exh cross over in the intake manifold.
There should be a valve in the exh just after the manifold but before the Y pipe. The 300 six has a valve in the exh manifold.
Make sure this works and is not stuck closed sending hot gases to the intake manifold.
Better yet just wire it open so it cant close.
If you have a v8 manifold off that has a cross over you may want to also block the cross over so gases can go thru.

You can also try a different brand of gas as some have a different blend that might not be as bad.
In the end keep the carb as cool as you can.
Dave ----

PS: wait till you truck sits for a week or more and you have to crank it a lot to refill the carb.
No fuel did not drain back to the tank as there is no way that can happen.
Search for this also.
TODAY'S FUEL

 

So does the fuel just vaporize and create a “flooding” type problem from the intake being filled with fuel vapor? I’ve heard that today’s gas isn’t as good for carbs, will higher octane help this problem or is keeping it cool the only solution? I installed a carb spacer made of some sort of plastic that is supposed to keep heat off of the carb and it seemed to help but it still happens sometimes. It doesn’t have a heating plate and I removed the egr plate (which was disconnected and plugged by a previous owner) to have room for the spacer I added. I assume the intake manifold has to come off to block the crossover? I’ll have to check on the valve in the exhaust, mine has factory manifolds with dual exhaust that I think is original but not positive, would my truck have 2 valves in the exhaust or just one on one side?
Thanks Dave

 

Sounds like you removed the EGR plate and replaced it with a phenolic spacer, that's the best thing to do. you would have to remove the intake to block the crossover, and that's a good idea when the engine is apart but you don't need to do it and it's not your problem now.

First thing to do is check your choke, see if it fully opens when the engine is warm.

 

I’ve adjusted the choke and checked it several times since to make sure it isn't malfunctioning and it is open fully before it hits operating temp so that shouldn’t be my problem… I will block the crossover when I rebuild the engine but I’m trying to milk some more life out of this old 351m for the time being since it still runs pretty good.

 

My thinking on the flooding is that the vapores are heavier than air so when it gets pushed out the bowl vent(s) and cools it goes down the carb intake to the manifold floor and "floods" the motor.
It sounds you have done what you can to keep the carb cool with out pulling the motor apart like 440 side just leave it for now.

You should only have 1 valve between the manifold and the head pipe.
The valve closes and the hot gasses cant go out the pipe on that side so it is forced thru the intake and out the other side till the valve opens.
Now I dont think dual exh was factory on any pick up truck so that is after market / muffler shop setup.
Because of that the valve may have been removed but the only way to know for sure is to look.
If you have one make sure it is open, wire it open is best.

You might try a different brand of fuel.
If using ABC gas next few fill ups try XYZ gas and see if that makes a difference.
IF you can might try non-10% fuel to see what that dose but that can be $$ over the 10%
Other wise I dont have anything more on keeping it cool.
Dave ----

 

Fuel percolating .... back in the early '80s, I had a Chevelle, I swapped a fresh 454 in in place of the tired 396. I also put a freshened set of Holley 2 bbls on a Corvette Tri-Power intake on it. Was early spring, car was flooding at stop lights, I pulled into a parking lot out of traffic and popped the hood, pulled the air cleaner off, gas was bubbling out of the vents of all three carburetors. I poured a cold drink or two from a drink machine on the float bowls, I made it home, but I think was fresh summer gas in my tank that really cured it. A "junk yard find" 19" seven blade Lincoln 460 fan and a new set of intake gaskets and crossover blocks likely didn't hurt. I had already made myself a insulating shield for the carb bases.

Then there was vaporlock .... we used to put close line clips on the metal fuel line from pump to carburetor on our police cars. Setting there, idling, working radar, hot day, AC on, fast one go by, pull out into I95 and be ready to hit the median if it died. Maybe the clips didn't help, but they seemed to. I later tried and found that substituting a long length of rubber fuel line out in the air, supported, seemed to help in place of a steel line running tight behind the alternator and PS pump, etc.. next to hot heads & block. Just inspect and replace.

 

Is it just like a butterfly valve that blocks the exhaust? I’ve not had time to get under there and look to see if it’s there or not but hoping to get to that today. I usually always fill up at the same station so I’ll have to try the station across town.. none of the stations in my area have non or 10% that I know of

 

tbear853 I need to reroute my fuel line it hugs the motor pretty tight. If that doesn’t help I may try a bigger fan I hadn’t thought of that