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Re-routing carb vent lines so bike won't stall in water crossings

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I know this has been talked about before, but I thought I'd post some pictures and a quick description for those who might benefit. If you do any type of deep water crossing your bike will often stall a few seconds after the carburetor vent lines, which are hanging down below the swingarm, become submerged under water. Once the vent lines become submerged the fuel can no longer flow into the carburetor from the gas tank much like liquid cannot flow out of a straw when you have your thumb covering the end of it. The cure is to re-route some of the lines up higher than the water can reach. Recently when I had my carburetor off I modified the vent lines as pictured below. I ran this exact setup on a KTM for years without any problems or stalling through deep water.

IMG_2813.jpgIMG_2817.jpgIMG_2818.jpg

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It is a mistake to run vent hoses into the air box. You are getting away with it because the other end of the vents are open and when submerged in water the you are going slow. The purpose of the vents is to keep a standared reference pressure (atmospheric) on the fuel in the float bowl. Anything that upsets that standard reference pressure affects fuel delivery. Pressure in the air box is not atmospheric, at least no all the time. On a KTM, the "air box" is not very well sealed, more of an air chamber. Your vent design is good but I would move the end of the hose out of the air box to some place in still air.

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That makes sense. Thanks for that. I will take your advice and remove it from the airbox.

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I ran mine up to the stearing stem area, zip-tied them to the other throttle/clutch cables running there, and taped some foam over them. This way they are about as high as you can get them and no dirt is getting into the carb.

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It is a mistake to run vent hoses into the air box. You are getting away with it because the other end of the vents are open and when submerged in water the you are going slow. The purpose of the vents is to keep a standared reference pressure (atmospheric) on the fuel in the float bowl. Anything that upsets that standard reference pressure affects fuel delivery. Pressure in the air box is not atmospheric, at least no all the time. On a KTM, the "air box" is not very well sealed, more of an air chamber. Your vent design is good but I would move the end of the hose out of the air box to some place in still air.

Looks to me like he ran it through the air box and then on up toward the fuel tank. Are you saying that simply passing the vent hose through the air box will have an effect on it's function?

To OP, nice job but why go to all that trouble up through the box. I simply took those same two lines you siamesed into one and ran them straight up from the carb to the steering head area. Far easier, but not as clean as yours. Mine's gonna be easier to deal with with it comes time to pull/install the carb though, I'll bet.

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Looks to me like he ran it through the air box and then on up toward the fuel tank. Are you saying that simply passing the vent hose through the air box will have an effect on it's function?

To OP, nice job but why go to all that trouble up through the box. I simply took those same two lines you siamesed into one and ran them straight up from the carb to the steering head area. Far easier, but not as clean as yours. Mine's gonna be easier to deal with with it comes time to pull/install the carb though, I'll bet.

I ran two lines into one so I only had to deal with one line to re-route. The one line then goes up under the seat and then down into the airbox to hold it in place. I figured that was as high as it needed to be. If I ever get in water up to my a$$ I think the carb vent will be the least of my concerns. I understand the idea that there is a slight vacuum in that airbox, but in reality I don't think the carburetor draws enough CFM for it to matter. I ran my friends vent as pictured on his DRZ and he has never encountered any problems. I don't know why all the factory bikes come with all the vent lines hanging down that far. You will stall every time in a deep water crossing. Also, the vent lines are sucking in unfiltered air. Why this is not a concern for manufacturers, I don't know. We are very careful to oil and seal our air filters, yet the carb vent lines are just open to the dusty air.

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Ah so - I didn't look carefully enough at the pictures. I thought I was seeing the line come up through a hole, then out the top of the air box through another hole. Now I see that you brought it back into the airbox. My bad.

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Is there anythings that an owner of DRZ with a stock DRZ S carb could do to help out when going in the deep end? Am I correct to assume that the previous posts are all refering to the FCR?

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Is there anythings that an owner of DRZ with a stock DRZ S carb could do to help out when going in the deep end? Am I correct to assume that the previous posts are all refering to the FCR?

I have the S model and did the same sort of thing. When it is stock, you have a vent line that runs from the carb down. All you need to do is put a "T" fitting in the line and run one line up under the seat. You can leave the old vent line in place. This way your vent has two openings. Like the PO stated, you will be fine until you are running water deeper than your seat. I try to avoid that!

I just put the T up near the carb. Here is a blurry image:

IMG_0339.jpg

The top hose goes up and sits along the frame rail under the seat. I have it zip tied.

Edited by Mr. C

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Carb vents don't flow air. That is why they are not fitted with a filter.

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Carb vents don't flow air. That is why they are not fitted with a filter.

Huh?. A "vent" by definition is something that flows air. They do flow a little bit of air and there are companies that offer filters for the Keihin vent hoses.

Edited by q2quest

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Have had this discussion before. Call the "vents" what you like. They are atmospheric pressure reference signal routes. Easier to just call them what everybody does - vents. The only time they flow air is when the bowl is refilling (air flows out as the fuel flows in), and when the choke is on (there is an air bleed to the choke circuit inside the float bowl). Other than that, no air flow. The volume of fuel in the float bowl used by the motor is replaced by fuel from the gas tank. The volume of fuel in the gas tank used by the motor is replaced by air that enters the gas tank. Not normally a filter there but could probably use one. Yes, you can buy filters for the carb vents, but you can also buy a lot of things that are unnecessary.

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