I've removed my starter from the race bike and was measuring up the hole for a plug/cover, and I thought I might put a fitting in the middle and have a bottom end breather. Any thoughts on this? Are the gs motors known for building up crankcase pressure? I know the gs has one on top of the motor attached to the valve cover but I thought I read that some will drill it out bigger.

My big single had a bottom end breather tube right underneath the carbs. I stuck a k+n breather filter on the tube and ran it into my catch can.

Opinions? Any negative effects from adding a breather?

No negatives, but you definitely want to vent the crankcase. More venting should be beneficial in getting rid of hot air trapped inside. A kind of internal cooling.

There is already a breather tower on the top of the case, on the right-hand side, inboard of the engine number, that is threaded. I think this is used on 49 state models and the GS450's as the crankcase breather, but I'm not sure.  :dunno:

Interesting, I do have a california model engine, which I've replaced the ing. rotor with a 49 state. I thought that was the only difference between the cali and 49 state. Can someone shoot a pic of this breather? That way I can see if it's blocked off on my motor.

It's got a big bolt in it and a washer.

I was just thinking if you can use both breathers and install one-way valves and filters, so that the crankcase mounted one draws in cool air and the upper one expels the hot air, creating a kind of 'flow' keeping the engine cooler(?).

I know what you're talking about now. I think that actually has something to do with the transmission. I just had the engine completely tore down and I can't for the life of me remember what it does :dunno: