there is usually a rubber sealin the cap ur might be corroded
The vent hole can be very small so you might have to look for it. You've heard the term "your mileage may vary" - that's why different people with different styles will get different mileage on the same bike. I have the C90 and people claim to get 40 to 45 mpg. I'm lucky if i get 32. I had a Honda Rebel and was getting 60 while everyone else is getting 75 plus. I'ts just the way you ride it.I will take a closer look and see if anything is pinched or blocked. Thanks for the info!