another weil mclain gold!

This one won't fire on the first attempt ever, and sometimes will fire on the second attempt.  It also fails to fire at all, which is why the homeowner called...tired of resetting it.  These are the negative pressure gas valves.  Incoming pressure was 8", now when I tested the manifold pressure, it was supposed to be -.1 to -.2, but I was getting a -1.5" to -2.5" reading on my digital manometer, and it would not fire. I then noticed on the second ignition attempt, the pressure would go back to -.1 or -.2 and it would fire.  Tried that sequence a number of times, and it was consistently missing the first attempt with the higher vacuum, and then firing on the second attempt when the pressure was correct.  Got the boiler going for the night, was looking for any ideas you guys may have.  I was planning on pulling out the blower and cleaning, and having a new gas valve and ignitor on the truck.  Is it possible the burner cone is clogged?  Usually when I have seen that the pressure switch trips intermittently.  Would the cone have any effect on the gas pressure?  I would think it would cause a higher pressure (in the +) if the screen was clogged because it wouldn't be able to create the vac in the manifold but I seem to be having a higher than normal vac created which led me to believe the gas valve was the problem.  Thanks!