Here's a question, can the breather pipe in the rear of the crankcase be shortened because as standard it goes all the way down & into the oil in the sump?. I think that if it's below the oil level then it can't 'breath' very well & will slightly pressurise the crankcase.
Any thoughts or has somone done it? :D :D

Yes it can just stick a small engine breather pod filter on or a diaphram filter of the carbs on i have had no probs with this set up will take photo and post up later. :D

The brether's on the outside the oil in the sump is on the inside of the engine.
It's just a vent so as long as it goes somewhere it's ok. As LAJ says if you shorten it you really need a filter to stop oil from coming out over the engine

I meant the pipe on the inside of the engine chaps, It sits under the oil level which means it can't vent to atmosphere properly. I want to cut it down so the pipe is above the oil & can vent better, I think it's put where it is by Yamaha to stop it pumping out oily air for emissions reasons. I've got a catch tank already fitted as it's my race bike. :D

The oil level will be much lower when the engine's running though, and I doubt the emissions will be an issue.
2 things come to mind ... if Yam designed the engine to run that way then it's probably right and I doubt there's much if any gain over this stock position

That pipe sits in the oil right at the bottom of the sump so will be submerged even with the motor running , I know you can pick up a small amount of power as the pistons aren't pumping against air that can't go anywhere & this seems to be a poor way to vent the cases.

I know what you are talking about, the only saving grace is the fact that the breather is in the centre of the crank case and when the bike is banked over i presume it will be free from oil and able to vent. I would not think it would cause any increased crankcase pressure even if submerged (the oil would simply flow up the tube to compensate for any pressure)..............................................i think, maybe a little too logical.

I see what you're saying, I was just thinking if it was worth do before I bolted it all back together again & if anyone else had done it. I didn't want to cut it short & find out I'd cock'ed it up on the track when it pukes oil everywhere! :D

an old saying springs to mind, if it works, why fix it!! :D