Yamaha 60 2 stroke problems

[Highland_Pete]

We have a Yamaha 60hp autolube fitted to one of our dive club ribs and its giving us some grief.
Last trip out it lost power and plodded home on the middle cylinder, without missing a beat. We cleaned out the carbs and checked the plug packs / coils work. The engine now starts and runs on the middle cylinder but the spark on the top and bottom cylinders is week to nothing. If we swap the plug and coil from either of the non running cylinders to the middle one it still runs on the middle cylinder.
Any tips on what’s causing this?
Thanks

[carldalmas]

Originally Posted by Highland_Pete

We have a Yamaha 60hp autolube fitted to one of our dive club ribs and its giving us some grief.

Last trip out it lost power and plodded home on the middle cylinder, without missing a beat. We cleaned out the carbs and checked the plug packs / coils work. The engine now starts and runs on the middle cylinder but the spark on the top and bottom cylinders is week to nothing. If we swap the plug and coil from either of the non running cylinders to the middle one it still runs on the middle cylinder.

Any tips on what’s causing this?

Thanks

Check compression on none firing cylinders check two stroke mixture oil check bores check plugs
Warm plugs up over hot gase stove burn fuel off spin engine over with no plugs see how much fuel blasts out !
Fit hot plugs check sparks !