Slant 6 Help Needed

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bigboijc13

bigboijc13

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What would cause my '73 valiant to idle so rough in gear, while your foot is on the brake at a light, but when you take off and are driving, it seems to run smooth?

1973 valiant 225 3.7 liter, purchased after sitting for 5 or so years. Replaced so far:
Fuel pump, fuel filter, carb, plugs, cap, distributor, coil, ignition module, radiator, misc belts and hoses.

Thank you guys in advance....?
 
Did it start happening all of a sudden? Power brakes? A bad brake booster? Try plugging the vacuum line....could be a bad torque converter, could just be an engine that is out of tune....
 
No power brakes, but did find a vacuum leak at the carb. Fixed the leak and it seemed to idle much more smoother in gear. Will find out tomorrow on the trip to work. Wish me luck....:thumblef:
 
Those sixes can idle like a singer sewing machine. Smooooth. Rough idle is almost always a vacuum leak, then Carb mixture, then valve lash. Start pulling vacuum hoses and plugging while running. 73 has a few.
 
Just in case the vacuum leaks and carb do not do it for you......That year had solid lifters and it very well could never have had the valves adjusted. You need to take off the valve cover (get a new rubber gasket) and the mechnical adjustments are right there at the ends of the rockers. Good valve adjustment and free valve action is critical to the /6 smoothness.

Old fuel ingested into these engines can really show up as gummed/sticky/stuck valves. Did you clean the tank and dump all the old fuel? The valve springs are pretty light and so won't easily overcome stickiness in the valves. So you may be due for some valve cleaning, with this car having sat for a while. Sometime some Marvel Mystery oil in the crankcase will free them up, sometimes not.

Some Sea foam dribbled slowly down the carb while manually holding a fast idle will clean the intakes some but not do anything for the exhausts; that takes more work under the valve cover. Ideally, you pull the springs one at a time and clean the valves and guides from the top and put in new valve stem seals at the same time. Ask about the procedure if you want to do this so you don't drop a valve into a cylinder....NG!

Good luck with it!
 
I bought a 63 Valiant and the intake gasket was worn paper thin.Check for vac leak there.Slant sixes head heat cycle and the intake and exhaust actualy move around alot over time.Just a thought.
 
Lean idle. My slant six idled like that in gear, sometimes stalling for years. It was many bad Holley 1920 carbs. I had several professional mechanics looks at it, to no avail. Convinced me to learn how to fix cars myself than give gomers my money for nothing. 4th carb and it purred like a kitten.
 
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