Burnt Valve Question

[tri-power 250]

I am wondering if my 250 has a burnt valve. The engine runs fine at speed or above idle. It idles very rough, like it has a big cam in it, and rich.
Would this be a sign if a burnt valve?
Thanks,
Ken

 

[CoupeBoy]

A burnt valve creates a dead cylinder. If the valve burns through it will not build compression in that cylinder because it cannot seal when it is on its intake, compression, or exhaust strokes.

I have never had one so I can't give any specifics, but I think you'd notice if you were running on only 5 cylinders.

 

[First Fox]

I take it the problem just started? Could be any number of things. Some strange and sudden things happen to old engines. You might have blown a power valve, broken an advance spring, developed a faulty plug wire or vacuum leak. If it is running well at higher engine speeds it is not likely it is a burned valve. Any or all of these can lead to a sudden idling issue like you are describing. You will have to do some detective work and report back.

Autozone will loan you all the tools you need to diagnose a problem like this.

 

[xctasy]

A burnt valve creates a dead cylinder. If the valve burns through it will not build compression in that cylinder because it cannot seal when it is on its intake, compression, or exhaust strokes.

I have never had one so I can't give any specifics, but I think you'd notice if you were running on only 5 cylinders.

I drove my 1300 Kent engined Ford Escort 45 cwt van at 105 mph downhill once (it could only do 78 mph on a flat).

When I got home, it wouldn't idle. Compression tester yielded less than 60 psi in two cylinders, since I'd burnt out the exhast. Do a compression test, and if its lower than 115 or has a 20 psi inter-cylinder difference, since the I6 is the worlds easiest engine to do a head gasket on, pull the head and check the exhasts.

An I6 should run smooth if the ignition is within spec, the carb isn't leaking on the log head adaptor, hydraulic lifters are okay and the other vac lines are all there.

 

[Gene Fiore]

X2 on the compression test.

 

[tri-power 250]

A couple of weeks ago, It did have a vacuum leak. I did fix it. Saturday is going to be a busy day, fixing the car. I hope it's a power valve, I also have to fix a leaky heater core. I'm having a great run of luck!
Thanks for all your help.
Ken