My best friend has an 87 Banshee that always ran really good. One day when we cleaned the filter we tried a new type of filter oil. It started mising real bad. We figured it was the oil so we cleaned the filter again but went back to the regular oil. It still did it so we took the carbs off and cleaned them, it ran fine for about five minutes then started back up. Do you guys have any idea what it could be? by the way it has a fresh topend with good compression, and an airbox adaptor similar to the Pro-design.

 

Try new plugs... try to swap the plug wires from one side to the other and see if the other side is mis firing. Check the choke tube that connects the two carbs together. I'm not sure if that year had the e brake cut off or not but you can adjust the e brake cable and see if that helps.

 

Back firing usually means electrical. Check your plugs and all connections one little split in your wiring harness could mean disaster for such a sensitive electrical system.

Waymod

 

does this thing have the TORS system on top of the carbs? if it does, you may have disrupted something in the TORS system resulting in an electrical problem as the above post suggests. if a throttle cable is bound up, the TORS system will intermittently cut out resulting in misfiring issues....

 

You might try looking at the reeds. New filter oil could be causing them to stick.