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Join Date: Nov 2007
Location: Chandler, Arizona
Yes that vacuum port should be capped off. The easy way to tell if your bike is a CA model with an evap system is to remove the seat and look at the very rear of the gas tank. If there are two fittings on it, it is a CA model and has/had an evap system. If it still has it, it should be removed. Not just disabled, but removed. I don't want to be riding around on a bike with EPA crap on it.
Now, while only CA models have the evap system, ALL VN750s have the PAIR system. This is also EPA emissions crap and should be removed. Their is a large hose connected to a fitting on each head, both connect to a 3 way valve under the seat, and another hose connects to that and goes through a rubber grommet into the airbox, if you still have one. There is also a small vacuum hose, which would connect to the vacuum port in your picture. When this system is removed, everything needs to be plugged/capped off. The port on the rear carb can be capped off with an automotive vacuum cap, but I have had these rot fairly quickly, so I use a short piece of vacuum line with a small bolt stuck in the end of it, and stick it up under the tank. Where the two large hoses connect to the fittings on the heads, I have mine capped off with Dorman car heater hose delete caps from Autozone. The one that goes into the bottom of the airbox can simply be left in place under the seat with a bolt or some other plug stuck in it after removing it from the 3 way valve, or you can pull it out of the air box and find some kind of a plug that fits fairly tight where you pulled the hose out. That's what I did. Remember, this is an unfiltered hole in the airbox, and will allow dirt to enter if not plugged.
Now. if you have 2 fittings at the rear of your tank, find 2 pieces of rubber vacuum hose of the proper size, run them through the 2 holes in the frame, and down under the bike, and leave the ends open. One is a tank vent hose, the other one WAS an overflow hose that dumped gas into the charcoal canister if you actually filled the tank all the way full. I've had no problems with it, but if you find gas dripping from the bottom of your bike when you fill it up, it will be from that hose. If that happens, you can go ahead and plug it up.
I am a motorcyclist, NOT a biker.
1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike