81’ 4.9 cutting out intermittently

[NewEnglandF250]

Hey folks I really need some help here..... finally after 2 year’s I got my truck going took it out for 190 mile trip and after about 90 miles the truck with started intermittently cutting out upon deceleration after being under load....it keeps going but it seems like the truck shuts off for a split second......it has a YFA and I rebuilt it... new plugs, wires, cap, rotor, fuel filter, gas tank......thanks!!!

[1986F150Six]

With the engine cut off, remove the air cleaner and look down into the carburetor throat as you move the throttle cable. Do you see a stream of gasoline being squirted?

[Gary Lewis]

Yes, it could be a fuel problem, like David is suggesting.  And if so it could easily be a bad fuel pump or something as simple as rotten fuel hoses.

There are short sections of hose from the tank to the steel fuel line and from that line to the pump.  And if you have dual tanks there are sections from the steel lines to the switching valve.  I've had significant problems with those hoses getting so bad that they leaked fuel when the truck wasn't running and leaked air in when it was running.  And the air kills the vacuum the pump uses to move fuel.

Or, it could be electrical, as in the ignition module or the pickup in the distributor.  But one thing at a time - check out the fuel system.

[NewEnglandF250]

Thank you very much gentlemen!

[1986F150Six]

My response was based on the fact that the carburetor has recently been rebuilt and the stumble [power loss] is reportedly after deceleration. Perhaps the accelerator pump is not functioning correctly?

[FuzzFace2]

This is going to be a hard one as I under stand the motor does not shut off and stay off but shuts off and then back on when you let off the throttle.
Take it no tack in the in the truck? Maybe you could pick up a cheap one and just lay it some where and when this happens see if the tach is showing RPM or not.
Dave ----

[NewEnglandF250]

So I check the rubber between the steel lines and the seemed ok but I replaced them any way. Put a new fuel filter in. I cranked it Iver and was getting fuel but just a trickle, would definitely not call it a stream. I had my buddy crank it over and I noticed some fuel coming out of the pump at the seam connecting the top & bottom. I have a new one coming this morning so fingers crossed!!!

[Gary Lewis]

Yes, lets hope that's the problem.  But also check your oil.  Does it smell like gas on the dip stick?  A bad fuel pump can put gas in the oil and cause problems with the engine's bearings.

[NewEnglandF250]

Hey Dave, the only other way I can think to describe it is ...... it’s like flipping a kill switch off and then back on.

[NewEnglandF250]

Thanks Gary, spot on!!! It does smell like it has gas in it....

[1986F150Six]

Is the oil level higher than expected? Take the dipstick and away from combustible materials, hold a lit match to the oil residue on the dipstick. If gasoline is present, it will ignite. [Be careful!!!]

[82F150I6]

Are you still running the Carter YFA carb?  If so, this is a long shot, but it did happen to me once.

There are 4 screws which install vertically from underneath the carb body and fastens the body to the mounting base.  In my case these screws had shook loose and caused symptoms similar to what you describe.

With the air filter housing removed it was easy to diagnose...I grabbed the carb and was able to move the main body back and forth yet the carb base was still securely mounted.   Hmmmmm....not good.

The fix was also easy.  Remove the carb, a drop of Loctite and reinstall each screw.

Like I said, long shot.