Cylinder 4 not firing- HELP! Options

[tornik550]

Over the past three years, I have been working on my 73 914. The majority of the car has been rebuilt (except he body). I recently got the engine working well enough to drive. I have been driving the car to work the past two days. The engine seemed to run great. I am still fine tuning the carbs though. The engine is freshly rebuilt with about 200miles on it. It is a 2.2.7 l. The only thing that wasn't rebuilt was the heads (long story why).

Tonight, I made a few carb changes, drove the car around for about 15 minutes.. The car seemed to run great but idled a slightly rough. When I got back to my garage, I decided to re-adjust the idle mixture screws. I started with cylinder 4. I didn't notice much of a difference when playing with the screw. I noticed that there was a lot of cold condensation on the manifold for that cylinder. With the engine running, I put my hand over the trumpet on each cylinder one at a time. 1,2,3 caused the engine to almost stall, 4 made no change. I checked to make sure that I was getting spark to cylinder 4- I was. I checked to make sure that I was getting fuel to cyl 4- I was. I took out the spark plug and it had a bunch of black soot. I checked the others and they were a nice brown color. I felt the exhaust pipe for cyl 4 and it was about the same temp as the other pipes. I did a compression test and it read 90 on cyl 4. In my panicked state, I did not check the other cylinders.

I had previously gotten compression tests on cyl 4 at around 150. The problem is that I think that I may have screwed up tonight's test. When I did get the 150 on previous tests, I did the comp test properly. This time, I took the spark plug out, engine hot, put in the compression gauge, turned the ignition for about 4 seconds. Read the gauge- 90. Repeated- 90 again. I was panicking and tried to think of what the problem could be. Decided in my haste that I should check valve lash. I got the cover off and decided that I should stop and think about things overnight.

Any guesses?

Problems that I can see- compression test done improperly but would this make that much of a difference? Also, I did not check the other cylinders. Even if the compression was good- why wouldn't the cylinder fire or is it firing but just not well? Could this all be because of a tight exhaust valve? Or is all of this just wishful thinking. I suppose that bad rings are an option but they are brand new so why? I also supposed that I could have a bad exhaust valve.

Argh- since I just got my engine were I like it- I really hope that I just did something stupid and that there is not a big problem that will take the car off the road for a while.