'05 EC 300 billowing white smoke & running poorly

[Deerhon]

New here. '05 EC 300. Newer piston and rings (80 hours of mostly gnarly, low rpm single track). Never had any issues. Very recently began running very poorly with copious amounts of white smoke. Bike won't idle or rev past 1/4 throttle. Runs like the choke is pulled. Any ideas? Thanks for the help. Judson.

[Capz85]

Right hand crank seal??

[(F5)]

Water ingress. Read up on pump seal. I had to replace the shaft the seal runs on with my 07 but they are cheap. Check for water loss and gear oil contamination. Head o-ring could have gone too.

[Deerhon]

Thanks for the input. I suspected a right crank seal but wasn't sure the bike would run this poorly due to a crank seal failure. Checked the coolant, doesn't look as though I've lost any although I haven't ran it very much since it started having issues. Any fool proof way to check for a failed right crank seal or pump seal? Thanks for the help.

[GGRider01]

Also check the main jet.. it can fall out and act the same way.

[Zman]

Or it could be a water pump seal with a bad right crank seal

[Zrt1200]

I have had crank seals go on both sides of older Yamaha's so make sure you check your transmission oil to see if its low. Chances are its a water pump side seal but you dont want to fry your tranny!!

[Deerhon]

Thanks for the information. I have lost any transmission oil that I've noticed. It looked pretty good the last time I changed it too. "Piece of mind" sight glass on the right side shows full. I've had the carb off several times of late and haven't ridden it, so the main jet is still in place. Hopefully I'll have time this weekend to pull the water pump off and have a look at the seal. Once I figure it out I'll let you all know. Thanks for the help.