Cant stop the fuel leaks

Deadfrednc

Deadfrednc

New Member
Hey guys so i have an80 cb650c with keihin vb44's the 2 right side carbs have persisted on leaking fuel as if its flooding. Sorry I don't know the technical names but there is a small port on both sides of each carb on the outside about halfway up that they leak from as well as running out from inside the carb. I personally have cleaned them and rebuilt them at least 3 times and then in another attempt to fix the problem i toke them to a shop in town. He said he ran the carbs through an ultrasonic cleaner then reassembled them. I brought them home put them on and turned the fuel on after say 10 seconds or so no leaks bike engine off I rolled the throttle back and there it went pouring out again. I'm all out of ideas here the floats are none adjustable so that shouldn't be a problem. I've pulled the floats off sat them in a bowl of gas after an hour or more they were still floating I did notice a VERY lite scratch in the outside right carbs float valve seat but the other leaky carb was just fine. any ideas on what to do would be great.
 
OK so i toke the carbs back off and pulled the fuel bowls off the 2 leaking carbs and put the old float valves back in them. It seems to have "fixed" one of them the other #4 slowed down substantially but didn't stop. I used the wooden handle of a hammer and tapped the fuel bowl 3-4 times and it stopped. Now to me that means that a float is hung up either on the pivot point or the valve its self but when the bowls off i can move the float with no effort simply by flipping the carbs upside down and right side up they seem to have full movement. The valve itself has a spring loaded pin on the back side so i don't know if it is closing for sure or not. Someone please help before these carbs take a few blows from the other end of the hammer.
 
I think you've already found the culprit. It is your float valve(s).

Couple things can go wrong. If there is even a little bit of crap or gunk on the seat of the valve pin, it won't close all the way and fuel will continue to flow. Also, if the bowl gasket is too big and extends into the bowl, the float can hit it and get stuck. Also, if you have any pinholes in your float, they will fill with fuel and not float.
 
I've check the floats in a bowl of gas I even flipped them over so I feel safe saying they are ok. I've taken the bowls off multiple times and I'm very careful putting them back on to make sure the gasket seats properly and I've never noticed a pinched spot on the gasket itself. And as for gunk on the seat I've cleaned them including with a drill, q-tip and a brass cleaner/compound. Like I mentioned though there are lite searches in that particular seat not sure but could the float be hanging on that and if you think so how should I go about deburing or cleaning it up.
 
When you set the float height, did you do it on the bike with the gas on?

I set my float heights with the carbs on the bike and the gas turned on. When the float is set at the right height with my measuring tool, fuel stop flowing. This way I know the valve is working properly.
 
Gotta say I don't have much experience with Keihins and the ones I have had and worked on had metal tabs, but I would assume thats still how you would adjust your float level, by bending that tab. The exact measurent and procedure should be covered in your shop manual.
 
http://cosky0.tripod.com/imagelib/sitebuilder/misc/show_image.html?linkedwidth=actual&linkpath=http://cosky0.tripod.com/sitebuildercontent/sitebuilderpictures/page04-05.jpg&target=tlx_new

There ya go.
 
Also your float needle seats will have o-rings as well as the fuel transfer tubes between carb bodies. If these have cracks they will leak, but only after the floats close.
 
Your adjustment is the tab. Or at least you need to make sure that tab/tang hasn't bent in the wrong direction by checking the float height.
 
I know it sounds stupid and nobody believes me when I say you can not adjust or tune any part of these carbs besides the main jets size. But I have yet to find anyone that argued that with me to be able to show me how or where to adjust them.
 
Look at the picture in the link I posted there is no metal tang on the float nor is any integer part of the float metal. I can't see how it would be possible to adjust it without heating the plastic and bending it which to me doesn't seem like a smart idea. The carbs In the picture are exactly what I have but mine are much cleaner. Vb44a
 

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You are correct, they are not made to be adjusted by the plastic tang, or even adjusted at all. I did have to do a little reading as I have not crossed the 100% plastic floats before. :D

Are these floats new? I would assume that after much use those tabs would slowly bend in the opposite direction leaving the valve open. If they are old I would suggest trying to flex them back and see if it changes anything, or replace them for new floats.

I also like the idea of checking it on the bike with fuel on. I know this sounds messy and would require a pan under the carbs, but at least then you could manually push the valves shut and verify that they are sealing properly.
 
Thanks I believe I understand how you are suggesting to do this but could you go in a little more depth of how I would measure or the proper way to check this
 
Well float height is measured like so:


but I couldn't tell you what the proper float height is for your carbs, I haven't found the info with your all plastic floats and with non-adjustable floats it might not even be specified.

If you have the carbs pulled, I'd start by checking the float levels of the leaking carbs compared to the carbs that aren't leaking.

If they are off in height I'd try flexing the tab/tang or replacing all. If they are not, I'd hook them up to fuel and try to physically shut the valves with the bowls removed by pressing the float up or pushing a screw driver on the back side of the tab/tang. If that seals the valves and stops the leak you know its a float issue. If it doesn't you need to look into your valve sealing.
 
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