Carburetor vent hose too short - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 14 (permalink) Old 04-23-2018, 11:39 AM Thread Starter
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Question Carburetor vent hose too short

I was having issues with my bike running rough at cruise. It idles fine, and runs WOT fine, but at cruise it would stumble. A gust of wind would also affect it. Reading on this forum (specifically the linked thread referenced below), many reported the issue was a misplacement of Hose B.

"Carburetor Fuel and Vacuum Connections" (I'm new so I can't post URLs yet).

It's a 1989 that I've owned for 2 weeks. PO had it for 3 years. He knew of the rough cruise (and disclosed it to me at time of sale) but was unable to fix it. He had cleaned and re-tuned the carbs, and even replaced the fuel petcock, thinking it was plugged. I don't know it's history before the PO had it.

I pulled my seat and gas tank and found this hose was tucked under the rear of the gas tank. I tried re-routing it to the back of the right ear, but the only way it would reach was with a sharp kink in the hose. It definitely didn't have enough length to be fully inserted into the ear! The hose did not appear to be cut, or whoever cut it did a really clean cut! Has anyone else had this issue?

I ended up putting the hose back where I found it, but wrapped some course steel wool (what I had on hand) around it to reduce airflow around it. It seemed to do the trick. Are there any issues with this method as opposed to running it to the ear? I know for emissions reasons, putting it in the ear will draw in evaporated vapors to be burned, but I'm not concerned with emissions.
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post #2 of 14 (permalink) Old 04-23-2018, 12:37 PM
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Some of us (myself included) don't have the ears on the bike anymore. I have my carb vent tube tucked up into the hollow frame tube directly in front of and above the carbs with no issues.

Long story short, you're fine. Not a bad idea about the steel wool, either, so long as shavings don't get down into the carb thru the hose. Basically the hose just needs to rest in some dead air where wind can't hit it.

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post #3 of 14 (permalink) Old 04-23-2018, 01:25 PM
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The original vent line is cut at a 45° angle, so when it's plugged into the ear it can't get blocked against the back wall of the housing. If the hose has a straight cut, it's not the OEM configuration. I'm pretty sure there's no air connection there between the vent line and the air filter.

If you don't want to use an ear, the fuel sending unit on the bottom of the tank has a plastic cover on it, and there's a blank hose nipple on that cover which makes a good place to put the vent line. Mine is currently zip-tied to the frame under the center of the tank, facing the rear. If you get farther back toward the seat, wind can be a problem. Under the seat isn't a good spot either.

If the steel wool works, it's probably fine, as long as none of the wool ends up in the carb. That could be a nightmare to clean out.

If you want to use the ear, you can get a plastic 'coupling' to splice an extra piece at the end, which should be easier than getting to the line down at the carbs.

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post #4 of 14 (permalink) Old 04-23-2018, 04:51 PM
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I've heard of folks cutting the vent line at an angle, but was unaware it was done this way at the factory. As far as I know, and in regards to my 2002, the stock vent line was not cut at an angle, as I pulled mine and cut it that way myself.

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post #5 of 14 (permalink) Old 04-23-2018, 05:46 PM
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Quote:
Originally Posted by Knifemaker View Post
I've heard of folks cutting the vent line at an angle, but was unaware it was done this way at the factory. As far as I know, and in regards to my 2002, the stock vent line was not cut at an angle, as I pulled mine and cut it that way myself.
It's in the repair manual. Mine had the 45° angle.

edit: Might be in the owner's manual? I know I saw it in a diagram somewhere. Repair manual just says not too install the hose too deep in the housing.

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Last edited by Spockster; 04-23-2018 at 05:54 PM. Reason: Editing
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post #6 of 14 (permalink) Old 04-23-2018, 05:57 PM
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Found a pic of the cover on the fuel sender, arrow points to the 'fake nipple'. Disregard all those arrows on the petcock.

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post #7 of 14 (permalink) Old 04-24-2018, 10:38 AM Thread Starter
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I used a piece of fresh course steel wool, so I don't expect any small pieces.
However, now you've got me scared of breakdown over time!
I think I'll change it out to something else.

Thanks guys!


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post #8 of 14 (permalink) Old 05-11-2018, 12:17 PM
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Hey Spockster, Now that you posted picture I see what you mean .I have connected a drain tube to that nipple but will change it to the carb vent asap. thanks.

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post #9 of 14 (permalink) Old 05-11-2018, 02:38 PM
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I'm pretty sure the tube on the sender is just a failure drain. So if the sender leaks it won't drip fuel onto the engine.

I put a sintered bronze fuel filter inline with vent hose and tucked the end into the hollow frame mentioned earlier.

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post #10 of 14 (permalink) Old 05-12-2018, 05:33 AM
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yep that's what I thought, I wonder whether there was a drain line originally as without one would still drip fuel onto engine or maybe Kawasaki thought did not need it,Spockster called it a fake nipple so does the hole go all way through the plastic ?.

Vn 750 A2 1986 rebuilt engine, crank shaft, half casing,shell bearings,con rods,rear cylinder head,oil pump,water pump ,(had ceased bearing rusted up),tie bar upgrade,clutch basket drilled,front cylinder cam chains,toc springs,stator,shaved, rectifier,agm battery,solenoid ,starter motor (used) re-spray ongoing.
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