1996 40hp back fire

[onislandtime]

I have a 2 cyl 40hp 1996
backfires and no power SOMETIMES
Was thinking cdi yamaha dealer says thay don't go bad
Please any help
Thanks

[99yam40]

lean sneeze, clean the carbs

[onislandtime]

Carbs have been cleaned still sneezing after running in test tank for 10-15mins it starts to backfire

[99yam40]

like I said lean sneeze is my thoughts,
need to clean better
some times an ultrasonic bath is needed to get it all
or you have vacuum leak

Hopefully you followed steps in service manual to link and sync carbs after reinstalling

Timing is easy to check with timing light to make sure CDI is setting timing correctly