upsidedown

My 650 has an issue that when the engine is cold it runs fine but when the engine warms up the engine gets a really noticable miss at full throttle.
Doesnt matter about the revs just happens when throttle is opened up.
I have put a westcoast 30 ci ( i think) head on and is running a westcoast exhaust.
Replaced the coil and stator as was only getting spark on one lead for a while.
Anyone have any ideas what it could be??
Also running 38mm carb

fleshbazbo

You probably just have one fowled spark plug do yourself a favor and replace both plugs and spark plug caps.