Mikuni carb won't stop leaking
Discussion
The centre carb on my Kettle (Mikuni) has been troublesome since I bought the bike, with leaks. I've had it apart more times than I can count, checked the needle valve is seating and the float height is correct but it still pisses. So I bought 3 replacement needle valves and stuck those in this morning. Sure enough the outer two carbs are fine but the middle one still leaks. I've had it apart 3 times today, and each time before putting it back on the bike I have checked it and it seems leak-free, but once it's all bolted up it leaks again.
I'm struggling for ideas now. Is there anything else which could be causing this that I'm missing? The leak is coming from the overflow pipe. It's not a dribble either, it's as if you've left the tank tap open with no hose on it. it flows that much.
The replacement valves were Keyster; I know some will say only buy original, but the outer two are fine, and Keyster seem to have a good reputation as replacement items.
I'm stuck. I was going to run it down to the coast and have an ice cream this afternoon but given up on that now.
I'm struggling for ideas now. Is there anything else which could be causing this that I'm missing? The leak is coming from the overflow pipe. It's not a dribble either, it's as if you've left the tank tap open with no hose on it. it flows that much.
The replacement valves were Keyster; I know some will say only buy original, but the outer two are fine, and Keyster seem to have a good reputation as replacement items.
I'm stuck. I was going to run it down to the coast and have an ice cream this afternoon but given up on that now.
Mr2Mike said:
I'd check for cracks in carb body around the needle valve thread, and the other one is punctured floats. Does the needle valve work if you operate it manually i.e. no leakage when blowing into fuel inlet and pushing float up?
Floats are fine, they're brass and I checked them previously with the hot water method, and soldered a few pinholes up. I'll check for cracks them I didn't see any but wasn't looking for them either. Yeah, the needle valve works fine when the bowl is off and I blow through. I even started the bike with just the carbs on, no airbox, to check and it was fine then, but once everything is buttoned up and the bike is running, out it comes.The fuel tap is vacuum driven but has a prime bypass, it doesn't leak when it's on prime but does when it runs
CAPP0 said:
Steve Bass said:
I'd be looking at the float.
...jamming.....
Hmm, that's a possible, very difficult to check though!...jamming.....
If its not leaking wire the float up so it closes the valve and connect the fuel supply. If it's not leaking then you have a sticking float...
Steve Bass said:
CAPP0 said:
Steve Bass said:
I'd be looking at the float.
...jamming.....
Hmm, that's a possible, very difficult to check though!...jamming.....
If its not leaking wire the float up so it closes the valve and connect the fuel supply. If it's not leaking then you have a sticking float...
Had this a few weeks ago on a Honda Hornet 250 that I fettled for a mate. It'd been sitting for a number of years.
Number 3 carb would just PISS fuel. When I took it apart it looked fine. Had the carbs off and on twice thinking I'd missed something.
With the carbs off but the right way up and the float bowls off I could just detect some slight resistance to raising the floats. Really slight - almost undetectable on two of the four carbs, one of them being number 3.
So I got some 1200 grit sandpaper and "honed" the bore the needle valve sits in. Just rolled the paper into a tube and span it round a bit.
It's not leaked since. There must have been a slight but invisible step of deposits or wear that caused a bit of stiction....
Number 3 carb would just PISS fuel. When I took it apart it looked fine. Had the carbs off and on twice thinking I'd missed something.
With the carbs off but the right way up and the float bowls off I could just detect some slight resistance to raising the floats. Really slight - almost undetectable on two of the four carbs, one of them being number 3.
So I got some 1200 grit sandpaper and "honed" the bore the needle valve sits in. Just rolled the paper into a tube and span it round a bit.
It's not leaked since. There must have been a slight but invisible step of deposits or wear that caused a bit of stiction....
CAPP0 said:
Steve Bass said:
CAPP0 said:
Steve Bass said:
I'd be looking at the float.
...jamming.....
Hmm, that's a possible, very difficult to check though!...jamming.....
If its not leaking wire the float up so it closes the valve and connect the fuel supply. If it's not leaking then you have a sticking float...
If you wire the float up and run the bike you'll know if the fuel is passing the valve body.
From my experience, id say you've been lucky the keyster kits worked on the other 2 carbs, they dont have much of a reputation in the LC world which I found out for myself, to totally eliminate the needle, id get a genuine item from Allens performance.
http://www.allensperformance.co.uk/
Sounds like you've checked everything else, carbs do wear out eventually and its possible the seat itself is worn.
I hope you get it sorted anyway, would have been a fab day out on it today...Good luck.
http://www.allensperformance.co.uk/
Sounds like you've checked everything else, carbs do wear out eventually and its possible the seat itself is worn.
I hope you get it sorted anyway, would have been a fab day out on it today...Good luck.
@Podman, thanks, the Keyster parts seem ok on the other carbs but point taken. I do fully understand that you get what you pay for but the difference was something like £20 for a Keyster kit (which is everything, although I only used the needle valves and the gasket) vs, I think, £60 each from Suzuki for the needle valves alone! But maybe a bullet I'll have to bite. Although the carb leaked anyway on the previous needle valves, which was why I changed them. No idea what make those were.
I bought a kettle that had been restored it had the carbs rejetted using keyster kits and I had nothing but trouble with them, rough running, leaking and only getting 21mpg. Mikuni jets are hard to come by if it's the later CV carbs. I had mine vapour blasted and rejetted using mikuni jets and a bling finish done by Baz of the kettleclinic, it is like a different bike.
I have a pair of Mikuni's on one of my bikes. Is the float like a pair of ear muffs that rotate around a pin (not to blind you with jargon) held in place by tangs in the cast float bowl?
If so the cast part on mine that holds the pin in place had cracked slightly. It seemed ok when testing the bowl but with use the floats would break free.
As someone else said, what happens when you switch floats/bowls on the leaking one?
If so the cast part on mine that holds the pin in place had cracked slightly. It seemed ok when testing the bowl but with use the floats would break free.
As someone else said, what happens when you switch floats/bowls on the leaking one?
Moulder said:
I have a pair of Mikuni's on one of my bikes. Is the float like a pair of ear muffs that rotate around a pin (not to blind you with jargon) held in place by tangs in the cast float bowl?
If so the cast part on mine that holds the pin in place had cracked slightly. It seemed ok when testing the bowl but with use the floats would break free.
As someone else said, what happens when you switch floats/bowls on the leaking one?
The pins on the floats on my carbs are "free", ie not held in by anything, they just push out when you remove the float. The floats have never been free when I take the bowl off, they are always in place.If so the cast part on mine that holds the pin in place had cracked slightly. It seemed ok when testing the bowl but with use the floats would break free.
As someone else said, what happens when you switch floats/bowls on the leaking one?
Thanks though, something else to check later today.
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