hey guys just got a 91 spi in from a friend and its been forever since i have worked on the yellow 587 motor, this thing ran well on the hose and at the lake for 10 mins now it wont fire up, i have rebuilt the carbs, has good compression, has spark but its not as good as i would have guessed, looks to me as the mag cover is mangled up a little that it might be out of timing or so as it back fires out the carbs after cranking it for a while.

any ideas?????