elecrical problem??

hey guys, i got a 03 pro x 440, baught it at haydays and ran fine, fired it up last night and ran on the right cylinder until about 3k rpms then the left cylinder kicked in, both have same good compression and both are getting gas and spark, put it on the stand and it ran fine on both

took it around the yard and ran good, then let it sat and idle for about 10 seconds and the left cylinder kicked out again, any clue whats goin on????? cause i sure dont!!
HELP!!
thanks

the cap is good, same as the right one, still have no clue whats goin on