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How to stop the carb leaking

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How to stop the carb leaking
Started at 08:47pm on the 30th September, 2018 by daveh
daveh Subject: How to stop the carb leaking
Dear Bullet tinkerers, Can anyone help me stop my carb leaking? This is on an iron barrelled 350 from 2001. I can see drips forming on the bottom of the carb, and when I wiggle the bike there are many dribbles that come off. I already took the carb apart once - the float height was wrong and so I adjusted it. Took out the float valve, cleaned it, although it didn't look dirty. Squirted carb cleaner in the various orifices. Put it back together, and it leaks just the same!
Posted: 08:47pm 30th September, 2018
mart Subject: How to stop the carb leaking
have you checked for a punctured float? i had a float that very slightly rubbed against the inside of the float bowl. that stopped it from moving freely. are you using a fuel filter?
Posted: 09:08pm 30th September, 2018
daveh Subject: How to stop the carb leaking
thanks for that suggestion. I dipped the float in water and could not see any bubbles. But I will have another look to make sure it's not rubbing on anything.
Posted: 10:56pm 30th September, 2018
TONUPBOY Subject: How to stop the carb leaking
I realize not everyone has the desire to upgrade from the Mikcarb to a Mikuni, but I sure was impressed with the perceived quality in Mikuni's VM28-49 over the stock unit; I believe its float design to be superior.
Posted: 04:48am 1st October, 2018
daveh Subject: How to stop the carb leaking
Help! I'm still stuck. The carb still leaks. I just took it apart and replaced the float valve, and now the leak seems worse. I don't know what else to do apart from buy a new carb. Ton Up Boy - where would I buy a Mikuni?
Posted: 08:25pm 3rd November, 2018
stinkwheel Subject: How to stop the carb leaking
In my experience, float heights do not change themselves. So if it was wrong and needed to be adjusted, something has gone wrong with either the float or needle valve. I wonder if the tiny sprung pin in the top of the needle valve is stuck in or if the spring has failed.

Floats are usually obvious when punctured so if it were me, I'd be changing out the needle valve assembly which should set you back around £15 (part: 141969). It's a shame the service kits are out of stock for the 350s because re-brassing those carbs with japanese jets makes a world of difference, it was a really good upgrade for them.
Posted: 09:09pm 3rd November, 2018
ric Subject: How to stop the carb leaking
Did you replace both parts of the valve? Replacing only half of it isn’t always enough to solve the problem.
Posted: 09:12pm 3rd November, 2018
Alan R Subject: How to stop the carb leaking
Hi Guys------- well, you could try buying a new one ( On E-Bay at £38 approx ) ......... That'll get you back on the road straight away and then you can fiddle with the old one at leisure....My guess is that your present carb is Original Equipment which makes it 17 years old and they don't start off with the best of pedigrees, do they..............????
Posted: 12:25am 4th November, 2018
John L Subject: How to stop the carb leaking
Daveh - I would have serious doubts that spending "£38 approx."(really?) on eBay is the answer and will "get you back on the road straight away" - or that the need to replace the one part (the float valve assembly)of your 17-year old carb. that's actually giving you problems is a valid reason to condemn the whole carburettor, solely on the basis of its age. This makes altogether too many assumptions - diagnosis by substitution (and at a distance) is an expensive way to treat a problem, in my view.
Posted: 12:54pm 4th November, 2018
mart Subject: How to stop the carb leaking
Allens Performance are the Mikuni main agents in the UK- I recently bought a pre-jetted Mikuni for my 650 Triumph and it was spot on. Top quality too. John L is right- its not worth wasting 38 quid on what is probably Chinese junk. http://www.allensperformance.co.uk/
Posted: 07:28pm 4th November, 2018
Beezabryan Subject: How to stop the carb leaking
Does the engine run, has it been ridden?
If so how does it run?
Posted: 07:53pm 4th November, 2018
mart Subject: How to stop the carb leaking
did you reset the float level when you fitted the new needle? it might be slightly different to the old one. have you checked the float bowl gasket? to test the float valve: hold the carb upside down with the float bowl removed. gently blow through the fuel pipe and see if the valve lets any air through. if it does apply gentle pressure to the float with your finger and see if you can stop the airflow. alternatively: carb detatched from the bike, with the float bowl removed and petrol hose connected to the tap. hold the carb upright and hold the float up with your finger. turn the petrol on and see if your finger pressure prevents fuel flow. you'll need a bucket of course and a full risk assessment! drain some fuel into a clear jar and see if there is any crap in the fuel.
Posted: 08:17am 5th November, 2018
Mark B Subject: How to stop the carb leaking
At the risk of stating the obvious, are all the gaskets/seals in good condition and seated properly?
Posted: 01:15pm 5th November, 2018
daveh Subject: How to stop the carb leaking
PROBLEM SOLVED The brass floats had a leak inside, so fuel was getting inside, meaning they no longer floated properly. I had previously checked this by dipping it in warm water and looking for bubbles. There were no bubbles. This time I checked shaking it, and I thought I heard a subtle sloshing sound. So I sawed the offending float in half, and lots of fuel came out. Moral of the story: dipping brass floats in water is not a got method to check for leaks. Thanks to all those who suggested solutions.
Posted: 02:40pm 5th November, 2018
Wheaters Subject: How to stop the carb leaking
Dave, The usual method of checking for leaks in a brass float is to put it in a saucepan of very hot water, just off the boil. This causes the fuel inside to evaporate and bubble out. The float can often be salvaged by boiling all the fuel out (obviously not over a gas burner!) and then soldering over the leak. Done this a few times over the years on various bikes. Anyway, good to hear you've fixed the problem. I presently have a similar issue with one or two of the four carbs on my Honda CB750 Nighthawk - the floats aren't leaking - but they are made of plastic anyway so replacement is the only way to fix a leaking one of those.
Posted: 08:54pm 5th November, 2018
John L Subject: How to stop the carb leaking
daveh - Good to hear you have it sorted. These things usually have a very simple cause - but that doesn't necessarily make it obvious at the time.......
Posted: 09:50am 6th November, 2018
daveh Subject: How to stop the carb leaking
AHH! Problem not sorted. I having left the bike parked overnight with the fuel tap on, it is now dripping fuel again.
Just to recap - I've already replaced the fuel hose, fuel bowl gasket, float valve assembly, floats, and checked float height. I've checked the float valve with the bowl removed and fuel hose connected - it seems to work very well with light finger pressure on the float enough to stop the flow of fuel. The bike itself is running very well.
I'm now going to check that the fuel is clean. After that I don't know what else to do. Your ideas are welcome.
Posted: 10:21am 7th November, 2018
Aethelric Subject: How to stop the carb leaking
I saw this post on another (BMW) forum about a dripping Bing carb. It seems appropriate.

I once sent a fairly intemperate letter to Bing on this very topic (yes it was that long ago in the time before emails). They replied "We do not make petcocks, we make carburettors. When you leave your bike, turn the petcocks off."
Posted: 10:35am 7th November, 2018
Beezabryan Subject: How to stop the carb leaking
I'm with Aethelric :)
Leave now well alone, go for a ride, clear the head and as you approach home reach down to the petrol tap and turn it OFF.
Happiness :)
Posted: 10:41am 7th November, 2018
John L Subject: How to stop the carb leaking
daveh - Oh dear....sorry to hear the problem persists. I didn't mention it at the time, but I had a similar problem on my 500ES Bullet (sold 4 years ago). The Mikcarb began to leak when the bike was left standing for a few days - but this only manifested itself when the fuel was turned OFF - made NO sense whatsoever. After checking out the cause of the leak I eventually replaced the float needle and seat and checked float level, etc. after which the leak ceased. I then experimented with the the fuel tap (which itself must have been leaking - how else could the carb. leak with the tap turned off?) and tried leaving the fuel pipe disconnected from the carb. (but pointing into a container for safety) after parking the bike up. I was unable to get the tap to leak. My bike also started and ran perfectly OK. Only observation I would make re your problem is that it is generally considered bad practice to leave this type of machine parked up for anything more than a few minutes without turning the fuel OFF. You could give this a try, as well as turning the fuel OFF before you park up, leaving the engine to run until it stopped with an empty float chamber. If it's dirt in the fuel it'll probably drive you nuts.........DAMHIK
Posted: 11:04am 7th November, 2018

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