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Thanks for reply WFO-KZ
Yes I've bech tested it numerous times between trying different float heights ect, still leaking. I have just read a post on a KTM site about polishing with wooden dowel. So I'll give that a whirl tomorrow. Fingers crossed

KTM post read

Re: Non serviceable needle seat?

Take a wooden dowell a slightly smaller diameter as the needle orifice; grind a bevel on the end to match the bevel of the needle. Chuck the dowell up in a drill, add valve grinding compound to the bevel end of the dowell then grind a new seat in the needle hole. I think you will be surprised how well this works.
 

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Ok good. As long as you tested with gasoline pressure and not air pressure. Let us know how the valve grinding compound works. Also have you bought new needles? They are still available.
 

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Yep, got new needles. Even cleaned up old ones incase they worked, but still leaks.
Definitely tried all the obvious things. Only thing I can think of is the bike sat for a long time and somehow the seats corroded a bit to make them not seal. Anyway I'll try the dowel trick tomorrow, as I'm at the point of going to try and find another set of carbies, so nothing lost.
 

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By 1981GPZ550: I am sorry you are mistaken and do not understand the system. The vacuum petcock is a secondary backup device in case the carb fails to work properly. As noted in another thread no manufacturer designs and builds carbs that leak. They leak do to some failure. You are way off on your assumption....

A class in logic & common sense seems warranted. You say the petcock is a secondary backup, but then say no mfg designs a carburetor to leak? Then why install the automatic petcock if nobody designs a carb to leak? Why?, because in real world conditions carburetors can leak. Even properly maintained carburetors can leak*. Ideally, yes, ever single carburetor ever installed on a motorcycle should be maintained & operating perfectly. How many carburetors is that? Probably millions. To expect every carb ever made to work perfectly would be ridiculous. And that is one reason Kawasaki & others installed the automatic vacuum petcocks.

ps: I'm talking about little periodic dribbles of fuel, not a continuous dripping leak that can flood the engine, airbox or garage floor. It's up to the rider to assess the amount of leakage & then decide what should be done. common sense type stuff.
 

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Do engines develop oil leaks, yes they do, was this the designers intent. Every machine and every component ever designed by man is subject to failure. If an engine leaks oil it is due to a failed seal, a failed gasket or porous casting. This is not a normal condition. If a carb leaks something is wrong. Very rarely does a mechanical device repair itself, the problem usually gets worse over time. It is very simple, if a carb leaks it needs adjustment or repair. The point with the petcock is that the manufactures know very well that some percentage of the carbs will develop problems if only a speck of dirt between needle and seat. They provide a backup system not to cure the problem to to stop uncontrolled fuel lose until repairs are made. It is possible and normal to have some fuel exit the overflow in extreme conditions such as wheelies or a tip over. I have been at this for fifty years and I repeat, healthy carbs do not leak. I hate to see any leaking carb go unpaired as if the problem escalates it could endanger the rider. One of the sneaky problems with fuel and oil leaks on a motorcycle is that unlike a car when a motorcycle is traveling straight ahead a significant portion of the tire is not contacting the road. So a relatively small leak can go unnoticed as it contaminates the sides of the tire. All is good untill the rider leans the bike into a turn and the tire rolls onto the slippery contaminated surface. Every rider makes their own decision as to what risk they are willing to take, you want to ride with a leaking carb that is your choice. I am only explaining that leaks are not normal, the petcock is no substitute for repair. I would never let any motorcycle I had in the shop for repair leave with a leaking carb.
 

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So we have some common ground. Martin-CSR says "It's up to the rider to assess the amount of leakage & then decide what should be done" and GPZ550 says "Every rider makes their own decision as to what risk they are willing to take, you want to ride with a leaking carb that is your choice"

So relating this back to 84kaw's problem, if he is unable to stop the leak and if he is unable to source new carbs then he has a choice; he can rely on the vacuum petcock or install a manual petcock or he can junk the bike. If it were me, and the leak was a minor one, I know what I would do. If the leak is minor, a running bike will likely consume more fuel than the leak anyway, so there won't be spillage while riding it. But again, it is a rider's choice which is what both of you are saying.
 

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The carb on a motorcycle is not much different than on a lawn mower. Most older lawn mowers didn't have any type of shutoff for the fuel. Unless there is something worn or dirt gets under the float valve they don't leak. My guess is that the automatic shutoff is because of EPA rules. The Carb bowl is vented to allow it to operate. This will allow gas to evaporate from the bowl. If the fuel isn't shut off it will continue to refill the carb bowl. More evaporation more pollution. Cars and CA bikes have charcoal canisters to absorb the fuel vented from the tank.
 

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I would like to start by making a general statement. I am a retired professional mechanic and I follow multiple forums. Auto, motorcycle and aircraft. There is much valuable information from very competent posters. However there are also posts from those who have perhaps rebuilt a couple of sets of carbs, adjusted valves and perhaps rebuilt their clutch. These people make all encompassing statements of fact, in which I believe are all made in complete sincerity, but are simply false. One of the above posts states that no metal to metal valve can produce a complete seal. Wrong. For decades one of the final tests for a valve job is to fill the port with solvent, if it leaks past the valve you have more work to do. no leakage, good to go. The valve to valve seat is a one hundred percent metal to metal seal. Very hard for those who are just learning to separate accurate advice from that given by those who think they know but do not truly understand the systems they are commenting on. 84 Kaw, at this point I would suggest you purchase new inlet valves and seats. Install, set float level and go from there. Also when cleaning carbs it is important to always blow compressed air in tn the opposite direction of normal flow.
I totally agree with you about metal to metal does in fact seal. I have a question for you and need some advice. I have a carburetor WE-18 series. on an outboard motor. I just got this and rebuilding carbs. Metal needle to brass seat. befor lapping them, should I put needle in brass seat and lightly tape with a hammer just a light strike? I heard this is coing it. steel is hard, brass is soft. it pushes brass around steel vale to help seal? thanks
 
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