'85 Big Red Missing and Backfiring

[Sheemer]

Hi. My '85 Big Red misses and backfires, but only in 5th gear and only when I go faster than 45 KM/h or so.

At the suggestions of people I know I have changed the carb and gas line, the coil and spark plug, as well as the CDI box. The issue still persists. If anyone has any suggestions or has fixed a similar issue I would appreciate any input. Thanks.

[Thorpe]

Probably carb issues... Sounds like its leaning out on the top end... High speed Jet too small?

[jb2wheels]

Are the carb vents in place and routed correctly?
I've seen issues like this on street bikes when the carb vents aren't routed right. At higher speeds, they get in the airflow and pull a vacuum on the float bowls. Something to check anyway.

[specsec]

Could be the timeing too, when you get the engine backfiring it could meen that the exhaust valve is open a bit when the fuel ignites. if it only happens at high speed its only slight. maybe timeing stuff cant keep up.