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Discussion Starter #1
Hello Forum peeps, newbie here. I've had the VN750 about a year now. Had the carbs rebuilt by a local shop here in south Florida and the bike is running well. My question is about the open vacuum port in the picture. Pretty sure there was a tube connected but mechanic says not. Should it be capped? Thanks in advance
 

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If you still have the emissions equipment in place, that vacuum port is connected to the air valve system (which has 2 big hoses, one going to the exhaust of each cylinder jug, and 1 small hose which runs to the vacuum port)

If the emissions equipment has been removed you can cap off the vacuum port.

Where does the disconnected hose in your picture go to?
 

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Uber's probably right. Mine has a hose on it that runs off to the left (rearward) and disappears underneath the tank/seat area. My bike is totally stock (except for MCCTs). I'm thinking that black hose shown dropping down may be the one that is supposed to go up behind the right-side air filter.
 

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Good point about the airbox drain hose. Let's try and demystify this a bit, shall we?

Left Carb Vacuum Port -> Fuel Petcock (Left-side of gas tank)
Right Carb Vacuum Port -> Air Valve (Underneath seat, near battery box) -OR- Capped off
Top of Carbs Vent Ports -> Tee-Fitting -> Back of Right-Hand-Side Air Filter Box
Front Bottom Air Intake Box -> *hangs freely beneath bike*

There's a buncha other hoses, but these are the most common ones I recall seeing questions about
 

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Discussion Starter #5
I dont think the bike has emissions, not sure what it looks like. The hanging hose i believe goes to a tee between the two carbs? Maybe? Will try to investigate this weekend. If i put my finger on that open vac port the idle goes from 1000 to around 2000. My point to the mechanic was that the port is drawing in unfiltered air to the carb but he didn't seem concerned. The bike is running well and i'd like to keep it that way. If anyone here knows a good mechanic in south Fla let me know please. I did do the mccts, oil an fuel petcock myself but the carbs were to much for me to handle.
 

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Wow, that mechanic is dead wrong and he didn't connect things up the way they're supposed to go.

This should be an issue you can fix, though, unless you want to take it back to the mechanic and tell him he did it wrong and that you've confirmed it with fellow VN750 owners, but at this point I wouldn't trust their word or work since they've already flat-out lied to you. A vacuum leak is a serious issue, any mechanic worth their salt knows that.
 

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The hose that connects to the right side air filter just slips onto a tit on the rearward part of the innermost side of the air filter housing. Essentially this hose simply dead-ends on that tit. If you pop off the two bolts that hold the air filter housing to the frame (one upper, one lower) all you'd need to do is tilt it out a smidgeon so as to get a look at the rear of it. The hose is either there or its not.

The hose is supposed to end in a dead-air space so they (Kawasaki) put it there. If that hose ends in a place where the air moves then the engine can run like crap. But I don't remember if removing assorted emissions control stuff has anything to do with that particular hose or not.


Give me a few minutes and I'll come back with a decent pic of that area "naked" and shows a bit more detail than yours above.
 

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This pic was taken a few years back when I was changing out all of the cooling system hoses and flushing the system. To your needs, it more clearly shows the hose that runs to the air filter housing. Your hanging-down-hose looks suspiciously like this one.

That thick hose that you see running horizontally from behind the air filter area off to the left is part what Uber was talking about belonging to the air valve system. It comes out of the head, which from this angle is behind the visible air filter housing. If your bike does not have this hose (and the corresponding rear cylinder one that is on the other side of the engine) then someone has removed the emissions stuff.

You can also see the small hose connected to your "vacuum port".
 

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Also, while I'm thinking about it, that hose you've got hanging down (that fits onto the air filter housing tit) could use a slight alteration. I'd snip the very end at a VERY slight angle. The issue is that sometimes this hose can bottom out onto that filter housing and again, the engine can run like crap.

By snipping a "slight" angle to the very end, it won't bottom out and "seal" itself. A 10 or 20 degree snip should do the trick. If you cut it at a larger angle, there may not be enough hose there to hold onto the tit.
 

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the carb vent hose goes into one of the places I circled in your pic, either is fine, whichever works best for you

plug it most of the way in so the hose doesn't bottom out inside the hole, this can block air flow in the vent hose and cause fuel starvation
you can also prevent blockage by cutting the tip of the hose at a 45* angle so it doesn't bottom out, your choice



blocking the vacuum port is a good idea for now. still need to figure out if your bike has the air valve system. look at the engine picture here, do you have a hose attached to the circled port? (there's another one on the other side of the engine coming off the rear cylinder, not pictured here)
 

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I took a second look at your pic and realize I see that you DO have the air valve system in place. I can see the hose coming off the engine port.

instead of plugging that vacuum port you need to look for the air valve.

1 - follow a hose coming from either of the engine ports. (see my previous post)
2 - if you follow either of those hoses back to where they meet you'll see a brass valve assembly with 2 of the big hoses coming out of it. there is a third hose coming out of it, which is a vacuum hose.
3 - plug that hose in to the right-hand-side vacuum port.

that will return your bike back to stock.


other people will chime in about marbling/coasterizing. don't get ahead of yourself. they'll be talking about another modification that is VERY well documented on these forums. look for a sticky/how to if you want to do that mod. we should not discuss it further in this thread.
 

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Its been a while since I looked at it but as soon as I saw uber's pic I realized/remembered its not a tit after all but as he circled.
 

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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.
 

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I don’t understand how this thread went 15 posts this is standard equipment on all VN750 and it’s a simple connection. Uber said it right from the start. It is not a CA option (as said directly above), it’s not special, it’s on every single bike. Carb to canisters under the seat. Don’t find a way to cover it up, cap it off, screw it up. Just connect it back with some hose from advanced auto for 0.30¢ a foot. Removing that properly involves block off plates and isn’t just a screw in the end of the hose fix.

Since you haven’t modified the bike they should be there. If they aren’t you may want to check and see if it looks recently removed and go back to the mechanic with a persuasion device to find out why he is screwing your bike up and taking your money to do so.

Here’s some pics. Hope you get it solved.
 

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There are 2 different emissions systems on Vulcan 750s. The evap system is CA only, though CA bikes were sold all over the country. The PAIR system, the one that uses the big hoses and 3 way valves and injects air into the exhaust causing backfiring is on all Vulcan 750s. Both should be removed at the earliest opportunity. I believe the small hose to the 3 way valve which is part of the PAIR (Pulsed Air Injection System) is the one that connects to the rear carburetor, and that is probably it that is hanging loose there, so yes, just reconnect it. BUT. When you get time, remove ALL that stuff from the bike. If it has an evap system (CA), the cannister and pump will be mounted just above the front end of the swing arm. You could just pull the hoses off and plug them up, but I wanted ALL the emissions crap off my bike. I even removed the bracket that the cannister is attached to, which takes over an hour, because you can only turn the bolts 1/8" at the time. IF your bike has only one fitting on the rear of the gas tank, it does not have an evap system, because the hose from that extra fitting goes to the evap system.

In that last picture on post #16, that gold colored valve, and all three hoses that connect to it shouldn't even be there. That's the PAIR system.
 

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I called it! I knew somebody would come in and talk about removing the emissions equipment!


My post above thoroughly answered the OP's question. One1 provided some good pictures showing you the "valve" and hoses. Let 'er rest

Don't go confusing the guy with an information dump
 

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Yes, you do have the PAIR system installed. All VN750s came with this. There is a small hose that connects to that valve that the 3 big hoses connect to, and the other end of that hose goes to the vacuum port on the rear carburetor. So just trace that unconnected hose to see where it goes. If it goes to that valve, then connect it to the vacuum port on the rear carb.

It's your bike, so you can do what you want, but I would remove that entire system. Get rid of the valve and all of the hoses. Cap where the two hoses connect to the front and rear cylinder heads, plug the vacuum port on the rear carb, and plug the hole in the airbox where the third hose goes too. You would be amazed how much crap there is. once you get it all off, it looks like you have an octopus in your hands. It seriously cleans up the looks of the bike, makes things a lot more accessible, and the bike will start and run better, the exhaust will not get nearly as hot, and it will not backfire. Basically what this system was designed to do is inject air directly into the exhaust system where it connects to the head to "help burn any unburned gas that might still be in the exhaust" Maybe it does, maybe it doesn't, but I don't really care. I like simplicity, and I don't like having a bunch of stuff on my bike that it doesn't need.

I just posted this FYI. All you have to do is make sure there is a small hose going from the rear vacuum port to that valve.

Also look at the rear of your tank, and see if it has fittings for one hose or two. If it has two, you have still another rats nest that needs to be removed.
 

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Sometimes you can really feel the love on this site.
I have found this site (and the Clymer VN750 manual) to be very helpful. My guess is that just about everybody here has removed all the emissions crap. Many have also removed the entire intake system and put pod filters directly on the carbs. But it is up to each person what they want to do to THEIR bike.
 
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