I doubt it is compression. That is a problem where it usually doesn't start at all. A lack of WOT is usually a sign that you are only running on one cylinder. Those motors will run remarkably well on only one cylinder but with a significantly reduced power at the high end. This is what racerone was alluding to.
To test for this I would do a cylinder drop test. You may have done it but to do it properly you should start the motor and let it warm up. Now bring it to a fast idle and then pull one spark plug boot at a time (use insulated pliers to avoid shocking yourself). If the motor dies when one plug boot is pulled you know that the other cylinder was not working or is very weak. If it does die on one cylinder, if you can, switch the coils and do the drop test again and see if the problem moves to the other cylinder. If it does then you most likely have a bad coil. If it doesn't you have another problem.
Now if you have another problem or if the motor dies when either plug boot is pulled then you need to do the following tests. A spark test would be my next test. With an external spark tester the ignition should be able to create a spark across a 3/8" gap on either cylinder. Does it? I would also do a compression test to ensure that the compression of both cylinders is within 10% of each other.
With the above tests you should either be able to identify your problem or at least have enough information to have someone here help you get to the exact cause.
