Carb Vent Lines Routing

[RodC]

My sons both ride 2003 200 KDXs. Both of them leak gas out of the vent tubes if you just lean the bikes over the slighest. I thought the float hight was too high but they both measure right.

The PWK on my KTM has the vent lines looped up over the carb and are routed to the oppsite sides of the carb. The right vent loops up and over and down the left side, and the left side loops up and over the right side. I'm sure this prevents a lot of gas from escaping.

Has anyone else experienced this problem or looped thier vent lines over the carb?

 

[canyncarvr]

A fluid that is fairly low on the viscous scale will seek its own level.

Presuming the vent tubes to be attached to something that is to be vented (stand tubes connected on the inside of the carb in some cases), how is such a loop advantageous to controlling fluid levels in the carb? Consider the state of fluid IN the carb if the fluid IN the tubes is above the bowl?

Maybe it's insurance protecting entry from the other direction.

KDXs most always suffer from incontinence. I changed my float level from 16 to 17mm with the result of much improved peeing (less).

Just as likely if not more likely is the float needle or its seat.

 

[jeffw]

The gas you're losing when you tip the bike a little is coming from the float bowl overflow tube, not the vent tubes.

The loop design of the vent tubes on other bike carbs is to prevent a vapor lock condition in rough conditions like big whoops. Then gas really can get tossed up into the vent tubes then, start to drain, but then be 'vaccumed' back into the bowl as the bike needs gas, causing a momentary vapor lock. The result is there's no gas in the bowl for the main jet to suck and it bogs momentarily.

PC racing makes a vent box that mimics the loop design and prevents bogging and the possibility of sucking dirt into your float bowl.

 

[RodC]

Thanks for the replies, guess I never thought before I posted, it would take a lot of gas to come out the vent tubes, it must be the overflow.

Still seems weird, maybe its the angle the carb sets in the bike because these 2 bikes leak more than any other I have had. I have had lots of pwk carbs and none leak as much as these two bikes.

 

[wibby]

I changed my float level just like CC, and it rarely pee's at all now.

 

[GreenPeace]

Ditto

 

[RodC]

Tx guys, I'll try a lower setting.

 

[canyncarvr]

A semantics issue.....

While some of the tubes are truly connected to vents, obviously the bowl overflow is one of the tubes. I didn't descriminate between the actual vents and the overflow. My point was that the vent tubes hadn't better have gas in them to extent there would be an advantage to a loop to keep the gas out, the issue being 'when they are leaned over.'

The kdx has a pretty good angle to it when it's on the kickstand anyway. After the kickstand bolt gets worn, it's worse. After you lever the weight of the bike against the kickstand after you bury it (and bend the kickstand) in a rut on an uphill it gets even worse.

Make sure the carb is located correctly if you use the oem reed boot. If you happen to use a radvalve (no locating slot at all), ensure the carb is upright as it should be.

 

[Jim Crenca]

I run stock float height have fixed all my wetting problems with a new float needle.

 

[JasonWho]

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[CaptainObvious]

Jason,

Those are vent tubes. Since the fuel level in the carb is in a constant state of flux, fuel and air are always exchanging occupied space. If the tubes get clogged you get a pressure differential inside the carb causing the bike to flood (air doesn’t escape – sending too much fuel to the engine) or starve for fuel (the carb can’t equalize the pressure by drawing air – creating a vacuum). In either case the bike will quit running.

I always remove the vent tubes and blow them out after a day in the mud. Always blow them out from the carb side.

Water could find its way up a tube but the bike would need to submerged in water for it to happen. Remember, water has a higher specific gravity than fuel and the tube and internal vents have been designed to draw/expel fuel and air.

Personally, I don’t like venting anything into the airbox as any thing in the airbox can find its way into your engine.

 

[canyncarvr]

re: 'Always blow them out from the carb side. '

So....sucking on vent hoses isn't a good idea?

;)

 

[Smit-Dog]

Originally posted by RV6junkie
... Personally, I don’t like venting anything into the airbox as any thing in the airbox can find its way into your engine.

:think:

I clean those tubes out when cleaning the bike, and always thought about re-routing them into the airbox, but realize that gas needs to be able to drain out. How about attaching a fine mesh screen to the ends of the tubes?

 

[skipro3]

An air stone from an aquarium supply source would work good. I use those on the air lines for barometric sensors on weather stations I maintain. It keeps bugs and things from crawling up the hose without creating a pressure differential, working more like a baffle. It would slow down the migration of a fluid though, and that may be enough to keep from sucking water all the way into the carb.

 

[jeffw]

Jason,

The PC vent kit T's the vent lines at each of the two carb vent outlets. One end of the goes to the airbox and one back done through your dog bones. The two lines that go to the airbox plug into a small filter which keeps dirt and dust from entering.

 

[JasonWho]

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[91KDX]

Do both vent hoses "T" off? This sounds like a good, inexpensive, do it yourself, idea!

 

[jeffw]

Yeah, both sides T. Run the top tubes to the airbox and duct tape a piece of an old air filter so that it covers the ends of the tubes and you'll essentially have a PC Racing carb vent system.

 

[JasonWho]

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