Ran Compression Check, now what???

[tnman]

I ran a compression check on my 86 350. All cylinders were runing around 170 except 1, it was around 90. I left the tester on for over an hour and it only leaked a few pounds. What should I do next? Does this sound like a burnt valve? I checked the valves and #3 seemed to be tight, this is the cyl that is only running 90lbs. I adjusted to the proper setting but it didn't change anything. Any suggestions?

[SpitAndDirt]

how many miles do you have on the truck. I have seen some cams develop flat spots, which may directly relate to why you are having a severe compression drop in that one cylinder. I might also suspect major carbon build up behind the rings, causing major blowby. Anything mechanical could be to blame with your year and mileage.

[lefty13lefty]

i would have to agree with spitanddirt it sounds like carbon buildup but it could also be a crack in the valve guide causing a drop in pressure. have a pressure check done on the head

[tnman]

I just bought the truck from a friends brother. The receipts show the new engine has about 40k miles on it. He said around 10k miles a rocker arm came off and he drove it that way about 30 miles to get home. He put it back on and adjusted the valves on that one side. I had a guy that built numerous 350 engines check it and he said the valves were too tight and he thinks that led to a burnt valve. I'm just trying to make sure before I pull the head.
Thanks for you input.