Kawasaki Vulcan Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter #1
New member checking in. I have a 2006 Kawasaki Vulcan 750 and I think I am experiencing some carbureator problems. Not really sure. Going up a hill it seems like a loss in power and backfires some. When I let up on the throttle it seems to run normal, when it doesn't need the power. Just wondering if there could be something in the carbureator that needs cleaning. When sitting still and holding the throttle at 2000 rpm's, I notice the rpm's on the tack fluctuates. Doesn't stay at 2000 rpm's. Bike only has 3300 miles on it. It probably set for a long time before I bought it and wasn't run a lot. Does anybody have any idea on what could be causing this problem? I would appreciate your input. Thanks, wrbish
 

·
Registered
Joined
·
213 Posts
first thing I would check.
there is a set of vent tubes between the two carbs that come together into a "T" fitting.
the 3rd end of this "T" is supposed to run off into the back end of the Left side stock Air cleaner/filter box.

make sure this tube isn't hanging out to open air. if it is, the wind turbulence at highway speeds is known to cause odd hesitation issues.

a second option for routing this tube is to connect it to the little nipple at the bottom of the gas tank where the fuel level sensor attaches into the tank.
 

·
Registered
Joined
·
11,753 Posts
a second option for routing this tube is to connect it to the little nipple at the bottom of the gas tank where the fuel level sensor attaches into the tank.
Bowl vents should always be referenced to air that is between air cleaner and carb. (factory location)

Try running some Seafoam in fuel before breaking out the tools.

That bike has low miles for its age, so it has done some sitting!
 

·
Registered
Joined
·
213 Posts
Hi sfair,

Sorry, but this is another instance where I am speaking out of personal experience. You are correct the carb float bow vents need to be open to allow for proper venting. Attaching the vent tubing in the manner which I described WILL NOT stop or hinder proper venting in any way.

Attaching the vent hose into the back of the left air filter housing is how it was attached by Kawasaki from the factory. Attaching the hose to the black nipple on the underside of the gas tanks fuel sensor is an option commonly used by those of us running a modified air intake system and no longer have the stock air boxes attached. It move the end of the hose away from turbulent air and still allows for proper venting.

as Stated above, yes, the carb bowls need open air to properly vent, BUT with the VN700 and VN750, if turbulent air is allowed to pass over the end of the vents, it does and will cause issues exactly as the OP described.

This is a very common issues discussed over at the forum: VN750.com

Furthermore, I do agree with you that it can also very well be an issue with the carbs being dirty/clogged due to sitting for long periods of time. Seafoam is a great idea to try running through the fuel system to try and clean it up before going into a full removal, tear down and cleaning. (assuming of course that the OP is in the US where it is available -Seafoam is commonly not available outside the US-)

I would even go so far as to drain the carbs, disconnect the fuel lines from the tank. Pout Seafoam straight into the carbs and let it soak overnight. Next day, drain out the Seafoam, reattach the lines, and run the bike to see if there is any improvement.

Photo of Stock air box for reference:



Back of Air box for STOCK mout point for vent hose:


One Note for this location. The end of the hose inserted into this location needs to be cut at about a 45 degree angle to be sure that the end of the hose does NOT seal itself off by making contact with the bottom of the hole.



OPTIONAL mounting point on underside of gas tank:


Closer views of what the hose is attaching to:

 

·
Registered
Joined
·
11,753 Posts
To maintain correct carb metering, bowl vents must be tied to air that is between air filter and carb mouth. The reason for this is that as air cleaner begins to plug up, float bowls are seeing air pressure that changes with the filter conditions to maintain consistent metering throughout the range of being a new filter to fully plugged up.

Tying into any place that just sees open atmosphere will upset this metering, even if the end of the vent tube is out of the flowing air.

I would be cautious in using Seafoam outside of manufacturers recommendations.
 

·
Registered
Joined
·
213 Posts
The VN750 carb vent tube was to open atmosphere even from the factory. The stock mounting location on the back side of the air cleaner box did not actually tie into the air filter in any way. It attached to the back of the air cleaner box solely to remove it from turbulent (flowing) air.
 

·
Registered
Joined
·
213 Posts
Are those vents not tied into the surge tank?
Nope. Connected to the back of the air box where I circled in red in the above photos. This 'hole' does not actually tie into the inner workings of the air box.
 

·
Registered
Joined
·
213 Posts
The surge tank connections (aside from the obvious air cleaners) would be the Crank case breather which comes off the front head between the head and the radiator, and the tubing for the reed valves which feed the cold air back into the exhaust to burn off excess gas fumes.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #10
I originally thought I had carb problems, but with the info you guys provided me got me thinking to check more lines and more wires. i've tried the Seafoam for the past year and another product that a motorcysle dealer told me to use and none of that fixed the problem; got me thinking there was more to check when he told me to check the vent line going into the back of the air filter. I found it was in place from the factory, so I checked the sparkplug & wires & I found front right cylinder wire was arcing out because throttle cables were pressing down on it hard & wore a groove in it. So I taped it up & put a piece of rubber block between them & it seems to be running just fine now, Hope that was the fix. Thanks for all the suggestions you guys gave me that got me thinking a little deeper to check more things. Now I know I need to buy a new wire. wrbish
 

·
Registered
Joined
·
11,753 Posts
The surge tank connections (aside from the obvious air cleaners) would be the Crank case breather which comes off the front head between the head and the radiator, and the tubing for the reed valves which feed the cold air back into the exhaust to burn off excess gas fumes.
It is standard practice to run bowl vents, for the reason described in post #5, plus then you have filtered air only reaching the bowls, but if the 750 is not so plumbed, then I will take my crow with a little ketchup, please!
 

·
Registered
Joined
·
213 Posts
Great wrbis,
Glad you got that sorted. I've heard of the throttle cables doing that on the 750 to some other people as well. Been awhile since that ones come up and didn't think of it, but it certainly makes sense. Good idea wit the hose a guard.

Heres a thought for the new spark plug wires:
http://www.ebay.com/itm/Kawasaki-Vulcan-VN-750-Spark-Plug-Cables-Wires-Black-VN750-/390822582580?pt=Motorcycles_Parts_Accessories&hash=item5afed75934&vxp=mtr

This was the route I went when one of my OEM plug caps cracked on me. NGK plug caps and core wire. This setup would be of a better quality then OEM.
you MIGHT be able to ro it yourself cheaper if you can source the parts locally, but for around $40, it's really not a bad deal.
(and no, I'm not assosiate with the seller at all :p)



sfair, thanks for sharing your knowledge. As a side note, another bike that isn't hooked up in manner you describe is the Honda Rebel 250. The carb vent is hooked to a T. One end on the T goes straight to the float bowl drain. then to another T that loops back up over the carbs and then down below the swing arm. I always thought this one was a strange setup.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #13
Carb fix

Thanks to you guys for your quick responses to my carb problem. Really appreciate your help. I have another question. Do you know what octane gas that works best for my bike that I should be using? Thanks, wrbish
 

·
Registered
Joined
·
213 Posts
Stick with 87 octain. Anything more is a waste and does not help performance on this bike.
 
1 - 14 of 14 Posts
Top