The plugs were just replaced along with a pair valve mod and 4 degree advancer and full Muzzy exhaust. The old fuel in the carbs had a fuel stabilizer mixed with the fuel before the mods started. I hooked up an auxillary fuel tank to check the engine and lube the engine parts. When the bike warmed up it had a off idle stumble but the engine runs good after the revs are up. Any ideas what could cause this?