normally my engine would behave pretty well if I can ride normally, but a vintage 4cyl bike just tempts me far too much to twist that throttle open quite a lot...
I noticed when I am on spirited rides out in the hills (i.e. riding aggressively our in the best Appalachian twisties I can hit in a day trip from home in SE Ohio & sometimes into West Virginia), I always come home with oil mist all over the undersides of the bike. this does a great job in preserving everything, making sure it will not rust/corrode, but makes for quite a messy bike. Rear tire traction is also a concern.
I started noticing that race bikes quite often had some sort of makeshift catch can. This is when I really started paying attention to this mod.the guy actually gave me a PVC catch can that was fabricated for his race bike when he parted it out. getting my bike ready for the riding season, I clean a whole lot of oil grime from the undersides of it, and so I referred back to this thread.
I currently just have a K&N breather filter on the end of the hose, and had it sitting on top of my air filter, so drips would just hit my K&N dual oval pods. I've still got a lot of misting out all over.
one of my first thoughts was just to get a bunch of fittings and connect all of the carburetor sync ports together with a brazed copper tube manifold that I would fabricate, so that I would have a constant vacuum on the crankcase. any moisture Vapors would get sent out the exhaust, and I don't think it's a problem to introduce minor amounts into the cylinder, as humid air gets sucked in there all the time. this might lead to a little exhaust smoking under aggressive riding, and could also maybe dirty the spark plugs up a little bit unless you are already running on the lean (hot) side.
with the factory set up, I noticed there is a drain hose on the bottom of my 77 GS 750 air box, and the oil would potentially just migrate down into the bottom if there was any condensation forming into liquid again. Vapor mist would of course get sucked into the carbs.
you probably wouldn't want to vent all of the vapors into one pod, as you would have uneven running conditions. it would be even worse if you vented it into only one synch port, as you would then have unmetered air going into that cylinder
the $45 Krank etc copy one way check valve is an interesting concept, and I am going to look at that KLR forum link in a minute. it seems like it from might quite possibly allow the engine crankcase to operate in a vacuum (reducing potential oil leaks and pressure against the pistons & possibly reducing blowby), as it will expel excess pressure, and then when the pressure drops, close itself, sealing the crankcase off into a slight vacuum condition. this would not help the oil migration out of the breather filter, but this seems to be a big positive if you are not running the hose into the air box or pods or synch ports
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