Hi again Fred

I was thinking again about the submarine - of course your talking about the bit thats attached to the side of the snorkel. When you said submarine i pictured a periscope !!

I have a similar little bottle on an RD125 and its function is explained in the manual. It's refered to as YEIS Yamaha Energy Induction System. On the RD125 it's mounted on the inlet tract between carb and engine. Its function is to improve intake efficiency in the low to medium speed ranges. It does this by reducing pressure variations in the inlet tract which exist in both two and four strokes by the action of the inlet valves opening and closing.
It goes into lenghty detail of what exactly happens but basically when the intake shuts the momentum of travelling air/fuel mixture in the inlet tract creates a pressure which tries to go somewhere. Rather than have it go back out through the carburettor it is diverted into this bottle which itself becomes pressurised long enough for the inlet to open again whereupon the pressurised fuel mixture can mix with the fresh incoming charge.

Now I know this is a different setup to what we have, our bottle is mounted on the side of the airbox intake (on the wrong side of the carburettor if you like), but the reasons for it being there must be similar. ie. to reduce pressure differentials in the intake system.

-- ralph --