2004 Hisun 500 carburetor tubing

[Supertech15]

I'm looking for some close-up pictures of the tubing out of the carburetor. I understand that these are important to the operation of the UTV. The manual does not show a good diagram of where these lines go and come from. Please help.   Thanks

[Ben1098]

The T hose would be the CV carb's atmospheric vent.  The problem with the open ended hose is bugs and dust.  Bugs build nests and block off the vent.  Dust ingestion is bad for the engine.  Older  motorcycles would have the open end routed to the INSIDE of the air box and it's own little filter.  Yamaha 750/920 Virago vents went to a pair frame mounted steel tubes......open ended.......wasps loved these open ended tubes under the steering head..

Test hose assy by removing the tube at the carb (between the CV slide and the intake horn).  Blow shop air thru the just removed tube and it should flow out both the ends.

Install a clean tube to the carb and mouth blow air into the tube.  You should have no resistance down to the carb bowl and and if blown hard enough, you can bubble gasoline up thru the fuel jets.

Function......the fuel bowl has fuel sucked up thru the pilot jet (idle), main jet, and the fuel enrichment (choke cable on the left in the picture.  For the fuel to flow, a pressure difference is required.......intake creates a vacuum relative to the bowl's ambient air pressure.  Also, the CV carb needs the pressure difference to open the slide against the spring.  For funnys, put your finger over the hose nipple and see how the engine stumbles.

Now, I see on the air intake rubber tube it has a molded push in tube mount....very close to the end of the tube in your photo.  Check around the air box......there might be a hose connector to connect to.

[Supertech15]

Thanks so much for the information. My other concern is where the bottom of the "T" tubing. Where does that go?

[Ben1098]

Open drain for dust and water to get in.  High water will get sucked in by manifold vacuum if a bug calls the other end home.  The vent inside the carb goes directly to the bowl.  Water sits on the bottom, jets cannot flow with higher viscosity water and DEAD.

[Supertech15]

Please see picture. Does the bottom of that tube stay off or does it directly plug into the tubing coming out of the bottom of the bowl?    Thanks

[Ben1098]

OFF....both the small tube and the bigger atom vent tube stay open.

The tube out of the bottom of the carb fuel bowl is smaller in diameter.  That is the gasoline overflow drain for the bowl.  Look at the bowl's other side bottom and you might find a screw head, OR a boss pad that COULD be drilled-tapped for the screw.  EPA restrictions and/or bean counters deleted the function.  This screw (with a tapered end) lets gas will drain from the bowl when cracked open.  The bowl drain hose should be open.  The external nipple the hose is connected to goes inside the carb to an open ended vertical brass tube.  Think of a standing drain pipe for a lake overflow.  Function is to keep a flooding carb from filling to the point where raw gasoline runs into the engine cylinder----wash down.

The atom vent hose bottom is an open drain.   TRICK--------squirt some oil into the hose bottom but now fill to the "T".  Blow excess for just a coating that keeps bugs from becoming a squatter.

Q. for you.  Picture is framed too low.  You routed the atm vent thru the air boot molded mounting.......DID YOU FIND A SPOT to connect to WHERE THERE IS FILTERED AIR?

[Supertech15]

Thanks  for the info. To answer your question is no. I noticed that a newer rubber boot between the carb and the air box has a place where tubing plugs in.

that black coupling that you see on the bottom of the hose and the the hose that goes to the bottom of the carb is a one way coupler. 

Also when I suck on the line for the atmospheric vent, the engine really sounds good like everything works great.

On 8/15/2025 at 10:42 PM, Ben1098 said:

atmospheric vent

 

[Ben1098]

If the new boot is a good fit and function, buy...... Cheaper than engine rebuild if you use on dusty trails. The boot might be petrified anyways.   Down side is there might have been different jetting and/or a different spring constant----the stiffness of compressing the spring.  The diaphragm slide spring selection is a calibration of spring stiffness, length, and the needle hanging out of the bottom of the slide.  The slide position (air flow and fuel from the main jet) = engine RPM.... is determined by the difference in air pressures vs the spring pushing it back closed.  These stupid "I need the more speed" wantabe racers have problems with the carb hop up kits like race and full race for crotch rockets-----which literally fouls the plugs when just idle cruising the WHIP.  If the air boot modification changes the runability, simply disconnect and and plug---most noticeable when the air filter is starting to get clogged----restricted......changes the designed pressure difference at the slide porting.  Try and see.