Hi All, New to forum but was hoping some one could help. I recently purchased a 1984 Yamaha TT600 project bike. Engine had been rebuilt when I bought it so I know very little about the engine set up other than it was done by an engine reconditioner. After getting bike back together I found the following. Engine has good compression, does not blow smoke or leak oil. It runs nice and quiet, no nasty rattles or knocks. Bike starts easily and runs well. Pulls hard through entire rev range. Runs a nice clean plug. Only issue is that the oil appears to be pressuring in the oil tank and a small amount of oil blows out of the tank vent tube. Not a huge amount but enough to make a mess. I have checked to see that oil is circulating through engine and all appears normal. I have also checked engine oil level when hot and have it set to run halfway between add and full mark. (About 1 litre difference in oil level between full and add mark on these old bikes.) This did not seem to reduce amount of oil blowing from the breather. I have another later model TT600 that does not have this issue. The 1984 model has crank case breather running direct from crank to the cylinder head. The later model has crank case breather running from crankcase to air box. The later model has no breather in the cylinder head. Other than that engines are the same. The build up of pressure seems to be occuring only in oil tank. (dry sump engines) I would be keen to hear from any one that knows these bikes or any one that has encountered the same problem. My gut instinct is to run the crankbreather directly into air box and run a hose from the cylinder head back into airbox as well. Any thoughts? Thanks Mark.