I have a newly aquired 56 F250 with a 272, which was running when I bought it 2 weeks ago.

First job I did was to replace dizzy cap, plugs, plug wires and install a Pertronix electronic ignition module with Flame thrower coil.

The motor starts readily but feels rough from insde the cab but smooth from the engine bay. Now heres the thing;

I can remove 4 plug wires and the engine idles with no change at all. If I remove any of the others it runs rough. Its as though its only firing on 2,3,5 & 8 and therefore only missing everyother cylinder - BUT every wire has a good spark.

I double checked all the wires and the dizzy cab, everthing is in the correct firing order. I checked TDC with 10 degrees advance and eveything lines up. I pulled the plugs and can see unburnt gas on those cylinders where I can remove the wires and have no change to idle.

I put shop towls in the plug holes of the 'non firing' cylinders and they pop out with a pop, so imagine I have good compression.

Any thoughts out there? Could it be a miss-alined timing chain or maybe the ignition is off, it has a 57 model year distributer. Should I put the points back in and see if that solves anything?

Any help would be much appreciated.

Oh the exhaust note does not have that typical Y block burble, I guess 'cos its only a four banger????

It could be a carb problem IF you have a TWO BARREL carb and only are getting gas to one of the two barrels. Much easier to check.

If you have a spark from all the plug wires check your carb. Pete

Thanks for the suggestion. I just checked and both barrells are giving good fuel.

And from what your original post said, you have gasoline getting to those cylinders that are not firing, and it looks as if you have compression. How did you test for spark?

If it was me, I would get a gauge on test your compression on all 8 cylinders to see what you have.

After that, I would test for spark with one of those spark plug tester gizmos...

If after those 2 tests show all the "explosion" aspects to be true, then you must have a timing issue.

If you have unburned fuel in the cylinders, then you know in that cylinder you either have no spark, no compression, or the timing is way off. Don't forget that the cylinders are numbered 1-4 on the passenger side from radiator to firewall, and 5-8 on the drivers side from radiator to firewall..

hope we can help you. These things are always frustrating. One time I forgot to put all the plug wires in a firing order that went counterclockwise! Talk about a problem...I had the misfiring and towering flames shooting out of the carb until i got that one solved.

The plugs, wires, cap, coil etc are all tip top.

I pulled the plugs again and all I got was stale fuel smell from the 'dead' cylinders. I did squirt some Easystart down the left barrell and did notice a change with wide open throttle.

As you suggest i'll clean out the idle needles and see what happens. I'll keep you posted.

Although this sounds like a stopped up main jet in the carburetor, blowing some air through the idle mixture ports is definitely easy to do.  Beyond that, check the gaskets under the discharge fuel nozzles and/or do a complete disassembly and re-cleaning of the carburetor body.