216 question

[1955 Eddie]

So I've gotten around to getting my 216 running. Things were good. Easy start, nice idle, no smoke And revved up fine.

Over the past week it developed a slight miss at idle and started to blue smoke At start up and all rpm ranges. Started to go through things and found that while the truck is running I can pull the spark plug wire off of the two back cylinders and no change in the way the truck idles or revs.

I have no experience with these 216s and don't know the overall history of the block. I replaced the cap, rotor, wires, plugs, etc before starting it. Easy fix? Need a rebuild?
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[dwcsr]

Do a dry and wet compression test and post the readings.

[Tims37chevy]

Sticky valves?

[mr48chev]

First do as DWcsr advised and do a compression test. I'd suggest pulling all of the plugs, propping the throttle wide open and make sure the choke is open and check the compression in all six cylinders.

Two dead cylinders side by side quite often means that the head gasket is blown between the cylinders. But you still want to know what the compression is in the other four cylinders before you do something like pull the head to do a quick head gasket change.

[dwcsr]

I should add that while its not un heard of for these 216 heads to crack, compression loss in two adjacent cylinders usually is not a cracked head. But if it is 216 heads are still around at reasonable prices.

[Speedbumpauto]

Doesn't the rear leg of that intake feed both 5 and 6 cylinders? If so, at idle and other high manifold vacuum situations, it could simply sucking air through a loose rear leg of the intake, especially considering how those things were held on. Compression test is a reasonable thing to do, however.

[dwcsr]

Originally Posted by Speedbumpauto

Doesn't the rear leg of that intake feed both 5 and 6 cylinders? If so, at idle and other high manifold vacuum situations, it could simply sucking air through a loose rear leg of the intake, especially considering how those things were held on. Compression test is a reasonable thing to do, however.

The manifold feeds cylinders 1-2, 3-4, 5-6 and could be leaking. But typically that would cause a lean miss fire not excessive smoke at all speeds. Lean miss fire should cause a puffing noise out the pipe. If the compression test shows good then look at the vacuum at idle and high speed to see if its normal and not bouncing. This video is good at explaining what the vacuum readings mean

Vacuum Gauge Test - YouTube