Misfiring, no power, stalling once warmed up

The Bike
<BR>
<BR>2006 Thruxton. Airbox replaced with K&Ns.Jets = 150/42. TORs AI removed, Cal emissions removed. 7 months old 10500miles (running with no problem for first 10000miles)
<BR>
<BR>
<BR>The Problem.
<BR>About 4 weeks ago bike started coughing and spluttering at cruising speed. Thought it was a tank of bad gas (been to a different gas station). Drained tank. Continued to cough and splutter, usually after about 10-15 miles riding. Idles fine when it happens, but gently rolling on the throttle increases revs til about 2500rpm then revs just drop quickly to about 2000rpm and fluctuate between 2000 and 25000. If I leave the bike to cool a bit (10-15 mins) It's back to normal. At first I could continue the rest of my commute (another 15 miles), but it has gotten to the stage that it's happening every 2 or 3 miles after the initial time on a ride.
<BR>
<BR>Yesterday I drained the tank completely again. Pulled the carbs and checked and cleaned everything - appears to be fine. I installed new spark plugs and a new fuel line. Re checked fuel filters and checked all electrical connections.
<BR>
<BR>It happened again this morning on the ride to work.
<BR>
<BR>Has anyone else experienced this? Any suggestion?
<BR>
<BR>Could it be a problem with ignition coil/leads?

[ This message was edited by: steelcap on 2007-01-22 11:44 ]