Help! Slant 6 keeps dying

[Fr. Kevin]

I have a 1973 Plymouth Valiant with a 225 Slant 6 automatic. When I drive 20 or 30 minutes or more highway speed (about 75mph) and then get off an exit, as soon as the car slows and I let my foot off the gas, the car dies. It doesn't sputter or shake, just dies. It starts back up but you have to keep it moving or it will die. After it sits for about a half hour or more it will run fairly normal but if you drive it long it does it again. If you put it in neutral when this happens it dies too. I have no idea why. Any ideas?

 

[mvh]

My 67 225 was plagued by this, also. Never got to the bottom of it, but I suspected the Holley 1bbl carb body -- the idle mixture screw had been tightened so hard that there was a crack in the carb wall. The hole was also ovaled out so that the mixture could not be precisely controlled. Since new bodies for these are not available I decided to go 2bbl.

People always say "vacuum leak" but I never found one.

 

[mguner]

Check the EFE valve under the intake (flap type valve on the exhaust) make sure it isn't stuck if equipped. Sounds like you are boiling the fuel in the carb and supply line to the carb. Make sure you have the fairly thick insulator gasket between the carb and intake, you may also slide a section of water noodle or pipe insulation over the exposed fuel line that runs along the intake and valve cover. If you have access also check to see what your total timing is with vacuum advance. If over 45 degrees try running with the vacuum advance plugged off and or adjusting the allen screw inside the vacuum pod all the way out till it skips and then thread in a turn.

 

[barbee6043]

with a plastic gas filter you can see if it is boiling. I know, steel is safer. a routine deal is run a FI hose across the valve cover to car from fuel pump, and ditch the factory steel line as it gets hot how it runs.
timing chain slop????? carb problem? move that fuel line is pretty much stardard for most slant guys now days with this sorry gas.

 

[AJ/FormS]

That is classic tight valves. As long as the revs are up, it will continue to rev, cause there is enough effective compression left to motorvate the car. But as soon as the revs come down, the compression is insufficient and the engine stalls. Let her cool down and everything shrinks and now maybe you have enough compression again to get moving.
If I am right and you continue to operate like this, you will end up with burned valves and that leads to a parked car or a sudden loss of spending money.
So my 2cents is set the valves. This is supposed to be done with an up-to-temp engine, but on a slanty it takes forever to get the cover off and by the time you get to the last cylinder, who knows what the running clearances will be. I set mine in the morning when the engine temp has stabilized overnight. I can take an hour or more, no sweat.
You have to use feelers that are no wider than the valve stem,or you will get an erroneous reading, cuz the stems hammer grooves in the rocker arm;and your feelers will have to fit into the grooves.
The valves have to be set with the lifters on the base circle.
I set mine at about .013/.022 IIRC;Loose is better than tight.