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Post by jimmyflawless on Jul 10, 2022 8:47:12 GMT
One of my carb bowls is dripping fuel through the little overflow tube underneath. The float and needle are obviously not blocking the fuel inlet opening as they should. Any suggestions how I can fix this? This is what I have tried so far:- - Swapped the float and needle from one side to the other - the leak follows that particular float and needle, so I the issue must be with that, rather than the carb itself.
- Checked that the float does indeed float
- Inspected and cleaned the needle, including giving it a little rub down with a scotchbrite pad
The float and needle move up and down smoothly. The needle blocks the fuel properly in the 'up' position - I have tested that by pouring a little fuel through and pushing it up and down with my finger. It just doesn't want to work when the bowl goes back on. It's very frustrating!
Also, I have attached a pic of my float and needle. I have noticed that there seem to be two types for these bikes. One with the needle like mine, and the other type where the needle has a little wire loop at the end. Which is better, and why? It looks like my float type is not adjustable, lacking the little metal tab that can be bent up or down).
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Post by BritPete on Jul 10, 2022 11:38:54 GMT
Had the problem
My view is the rubber in the float needle is end of life
New Float needle I think
Expensive from Silvers
Look on eBay- I sourced from China fraction of the price
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Post by duffer on Jul 10, 2022 12:47:12 GMT
Swap the bowls. See if the problem moves sides. Had a load of bowls that leaked.
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Post by buster on Jul 10, 2022 12:54:48 GMT
when you put it back together and fill the bowls with fuel have you given the float bowls a few taps? doesnt need to be hard, I use a couple of plastic handled screwdrivers and tap with the handles
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Post by BritPete on Jul 10, 2022 13:14:29 GMT
On the subject
Also, I have attached a pic of my float and needle. I have noticed that there seem to be two types for these bikes. One with the needle like mine, and the other type where the needle has a little wire loop at the end. Which is better, and why? It looks like my float type is not adjustable, lacking the little metal tab that can be bent up or down).
I think the NBs and the NCs had the type you have the earlier models had the wire loop
Can’t comment on best as always had the later models but there will be an opinion on here I am sure
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Post by dick on Jul 11, 2022 15:39:40 GMT
if you cant adjust the float height...it could well be putting to much fuel in constantly, the floats should be set at 15.5mm but if you cant adjust it, what does it currently default to ?
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Post by jimmyflawless on Jul 17, 2022 23:32:49 GMT
I don't know. What does 15.5mm refer to? Why do they need to be adjusted anyway?
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Post by buster on Jul 18, 2022 4:52:40 GMT
I don't know. What does 15.5mm refer to? Why do they need to be adjusted anyway? with the float bowls off and the carbs upside down you can measure from the aluminium face of the carb body (that the float bowls sit on) to the 'bottom' of the float (theres a good illustration in the haynes manual). a certain amount of fuel needs to be in the float bowls to stop fuel starvation at high revs, the float height ensures a safe amount |
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Post by johnfcbn44dx on Jul 18, 2022 5:35:52 GMT
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Post by jimmyflawless on Jul 19, 2022 8:47:30 GMT
Thanks for the info.
However, as mentioned, I have the all plastic floats. Not the ones with the little metal plate on them and the float needle with the wire loop.
Therefore I don't think there's any way to adjust them (nor do I think that is the issue anyway). I have ordered some new float needles in case they are the cause.
Doing some other digging on the Internet and Google it looks like another cause of leakiness could be the float needle housing, in particular perished o-rings. Does anyone know if the brass housings can be removed from our Keihin carbs?
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Post by grahamb on Jul 19, 2022 17:58:44 GMT
One of my carb bowls is dripping fuel through the little overflow tube underneath. The float and needle are obviously not blocking the fuel inlet opening as they should. Any suggestions how I can fix this? This is what I have tried so far:- - Swapped the float and needle from one side to the other - the leak follows that particular float and needle, so I the issue must be with that, rather than the carb itself.
- Checked that the float does indeed float
- Inspected and cleaned the needle, including giving it a little rub down with a scotchbrite pad
The float and needle move up and down smoothly. The needle blocks the fuel properly in the 'up' position - I have tested that by pouring a little fuel through and pushing it up and down with my finger. It just doesn't want to work when the bowl goes back on. It's very frustrating!
Also, I have attached a pic of my float and needle. I have noticed that there seem to be two types for these bikes. One with the needle like mine, and the other type where the needle has a little wire loop at the end. Which is better, and why? It looks like my float type is not adjustable, lacking the little metal tab that can be bent up or down).
HI have a look at the thin brass tube in the float bowl overflow. I found a crack down the length of one of mine It showed up as a drip from one of the overflow pipes Fixed it by soldering the tube along the length (outside)  |
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Post by duffer on Jul 19, 2022 19:15:51 GMT
Swap the bowls. See if the problem moves sides. Had a load of bowls that leaked. Absolutely. I rebuilt five pairs of carbs from bits. Loads of them had leaking bowls. |
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