#8 cylinder not firing at idle

The #8 cylinder is not firing correctly at idle.  The header port attached to that cylinder is not hot, as the others are real hot.  Now if i drive it or get the rpm's up, it will fire, but at idle it will  stop.  Changed plugs and changed igintion wire.

Compression test on the cylinder is 174 lbs.

My only though is that a head gasket might of broke and is leaking over to the cylinder.

Engine setup.  IR block, 66 mech heads, holley 4150 carb.  it has a long duration cam, don't know what it is.  the engine was rebuilt in the late 80's and was stored until the past few months.  I'm trying to sort thru and get the bugs worked out.

thanks.

[QUOTE=Bill427]

Compression test on the cylinder is 174 lbs.

My only though is that a head gasket might of broke and is leaking over to the cylinder.

[/QUOTE]

Have you checked compression on all cylinders, to make sure  they are close to the same... ?

Change your distributor cap, Its a long shot but it might just fix it. if its not the problem, then you just have a new cap. And try another plug and wire. I know you already changed it but its worth a try.

It is so hard to trouble shoot from a PC.

cj5nutz38958.3626736111

 I had this happen after a tuneup. Turned out the "new" cap was bad competely dead on one cylinder. I would also take a good look at that sparkplug.Kiltime38958.6424884259

Ditto on the cap.... happened to me too. the ugly visions went away quik when I stuck the old one back on for a looksee.

Dont forget to check for a vacuum leak.  That will also cause a miss at idle, and not at higher RPM with more load.

174lbs of compression is killer!!
A blown head gasket would not give you that much compression, so I doubt that is the problem.

I kinda agree with everyone else on the cap idea. I was thinkin maybe a broken insulator, or too large a gap on the sparkle plug, but you changed the plug.
Check the cap, and the rotor.

If you are still running the points set-up, check the lobes on the distributor that open the points very carefully. It's possible the lobe for that cyl. is flat, or is getting flat.

oh, yeah....and that vaccuum thing Ken said!! I thought about that too. It would really depend on if there is a vac. fitting in the manifold close to the #8 cy., unless there was a problem with the intake gasket.....I think....maybe....? Adams' Apple38958.7509490741

What everyone else said is more likely, but check the spark plug...maybe during installation the gap closed, or nearly so. Check the ceramic as well...if it's cracked, it will ground out.

i ordered a new cap and rotor.  I'll let you know.  I did replace the plug and wire with no luck.  Didn't find any vacuum leaks as of yet.  But you never know.  I'll keep looking.  Thanks.

[QUOTE=Adams' Apple] 
but you changed the plug. 
[/QUOTE]

But did you check the gap on the new plug... they are not always gapped  right out of the box either..

2 cruzn38959.8541550926