I have a relatively fresh rebuild with fewer than 2000 miles on complete rebuild through the short block and heads.

I have a backfire which I cannot tune out of the car. The backfire is coming from the passenger side tail
pipe (cylinder 1-4). It occurs "sporadically" during idle all the way up through WOT. Although, the backfire
frequency does reduce while idling when engine reaches 180 degress.

I checked the cylinder pressure and 7 cylinders register very close to 180lbs (+/- 3lbs), while the number
#1 cylinder came in at a feable 135-140lbs. I changed the plugs....the carb is jetted just fine but after 100
miles, I inspected all plugs and found the #1 cylinder was fouled and all other plugs were clear.

So, it's seems evident the #1 cylinder is the source of the problem.

I pulled all plugs and went back to the cylinder pressure check. Using a squirt can which has a levered
handle, I squirt one solid stream of oil into #1 cylinder and it still only registered 140lbs. With 2 additional
squirts of oil (now a total of 3 shots), the pressure is averaging around 160 with a max of 170lbs.

I'm concerned that the 3 squirts are screwing up the accuracy of this test as it may be possible that the oil
is now creating a seal at the valves.

Had I not shot in the additional 2 squirts, I was prepared to pull the passenger side head and inspect the
valves. Reminder, these heads were fresh rebuilds (guides/3angle/seals/etc) only 2000 miles ago.

I don't have a leakdown tester.

GUYS: What do you suggest I do next ?

Thanks in advance

 

If close inspection of the plug wires and distributor cap show no problems,I would remove the #1 wire just to make sure I was looking at the correct cylinder for the problem. Next I would remove the valve cover and inspect the valve springs,rocker arms and pushrods.If you still find nothing removal of the cylinder head will probably be necessary. If you have to remove the head and disassemble it,and it had replacement guides installed during the rebuild,make sure the guide is not moving in the head.I have seen this before cause a similar problem.