Question about 1986 Honda VT 500 C Shadow

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Leaking Fuel tap (petcock)

I have taken apart and taken apart and taken apart this evil little device. I have confirmed it is not the connection between the gas tank and the top of the petcock (giant bolt). after I take it apart and put it back on it doesn't leak until I hook the vaccum hose to the fuel pump and turn it on, then it really leaks. Also since I have put an inline filter on it with a longer fuel line (to accomidate the filter) you can only see gas moving through the filter if theres ALOT of of gas in the tank. Any Ideas anyone?

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  • cindi0418 Jun 08, 2009

    It turns out that the fuel supply valve was leaking due to overtightened screws. Proplem was fixed with the tiniest amout of gasoline safe rv. Thanks fro the reply.



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This sounds like a vacuum lock pet ****. 3 position? run, prime,and reserve? If you have it on pri, You will fuel running or not. If set on run, then you will only pass fuel when engine is running, and of course res. when tank is used up. Is this leak at the valve? or from the tank or internally flowing? Tis should also be a gravity feed fuel system, please correct me if I'm wrong. good luck. Long fuel lines are not prefered on gravity feed systems.

Posted on May 21, 2009

  • Ned C Cook
    Ned C Cook Jun 09, 2009

    Wonderful, that's taken care of. Safe Riding



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About after a min of the bike running gas starts flowing into the air box, its alos getting into th oil

First check to see if the oil level in your crankcase is too high. If you have a vacuum petcock malfunction (hole in the diaphragm) or if the fuel petcock is left in the prime position and a float needle sticks, then you get you get gas running into the cylinders, past the rings, and into the oil.
When you start your motorcycle the oil/gas mixture has no place to go, the crankcase is too full, and the mixture exits through the crankcase breather into the air box where it will ruin a paper air filter. Always turn your fuel petcocks off when not driving. If the petcock diaphragms are bad rebuild the petcock with K&L rebuild kits or replace the fuel petcocks with new ones. If the float needles in the carburetors are bad or sticking, take the carburetors apart, clean them, and replace any worn or damaged parts You will have to change your gasoline saturated oil for it will no longer properly lubricate your motor.
Just a note: in 1983 brand new Honda's would fill there engines in gas. All the components were clean and new. This can happen to any machine in any condition at any time. When not riding always turn off the fuel vales never leave them in the prime position.

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2005 1200 s. Since not being ridden for 6 to 8 weeks,gas has leaked into crank case.Fuel tap has no shut off,so I assume there must be a vaccume activated diafram,of sorts,in the tap.Could this be...

Either the vacuum operated petcock is stuck in the flow position as well as a float needle is stuck in the open position. Two things would have to be wrong so that the fuel would over flow the carburetors and run past the piston rings into the crankcase. Or, more likely, the vacuum diaphragm inside the fuel petcock is leaking and the fuel is flowing down the vacuum line into the engine. I would start by inspecting the vacuum fuel petcock. If you unplug the vacuum line and gas is dripping from the vacuum line then you will need to rebuild or replace the fuel petcock.

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What you are dealing with is a vacuum petcock with a bad vacuum diaphragm , in this case fuel is bypassing the petcock via the vacuum line and filling the engine (oil) with gasoline.
If you have a standard petcock that is leaking (not shutting off properly) or just left in the on position a stuck float needle will also fill your engine (oil) with gasoline. This can happen with a clean carburetor and a good float needle. It just sticks and you have to change your oil. If you have the kind of fuel petcock that allows you to turn it off when not in use , always turn off your gas when not riding.
You will have to change your oil if it is fouled with gasoline. I suspect a vacuum operated petcock is at fault. With standard petcocks I have seen new motorcycles in perfect order stick a float needle ( Kei Hin Carburetors ) and fill there engines and air boxes with gas/oil mix. On vacuum petcocks the diaphragm that shuts off the fuel flow is usually leaking and at fault.

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To see what is wrong you will have to drain the tank and take off the fuel tank outlet(filter assembly). What you should see is a tube sticking up with a fuel filter over it. The tube allows the fuel to enter the carburetor down to that level , when the fuel petcock is in the ON position. When you switch to RESERVE the rest of the fuel flows down through a hole at the base of the fuel petcock. If the tube is missing from the fuel tank outlet(filter assembly) or/and the actual fuel petcock switch (sometimes a separate part )you will not have RESERVE. Another way you have no RESERVE is if you have a leaking four hole washer in your fuel selector. This allows the fuel to flow from RESERVE to ON inside the selector valve(gas leaking in petcock but not escaping outside petcock). "Honda" has all sizes of 4 hole washers available, but , the assembly may not be designed to be taken apart and reassembled. In either case you may end up having to buy an assembly to fix your problem.

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My 2000 Harley Davidson Fatboy (carburettor / BT 88cc) is leaking fuel out of its fuel tap. It is coming out of the botton of the fuel tap where it looks like there should have a tube out but there isn't...

Your bike is equipped with a vacuum operated petcock. To check the petcock out, you must remove it from the tank. I usually use a large funnel and an empty fuel can. Loosen the petcock enough to allow the fuel to run out and use the funnel to collect the fuel in the empty can. Once the tank is empty, disconnect the fuel hose to the carb and the vacuum hose. Remove the petcock from the tank.

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Sounds like you've got a vacuum leak somewhere. Either your intake seals or the carb seal is leaking air. Have you replaced the air filter housing? On the Evolution and later engines, the carb is designed as a "spigot seal" type carb. In other words, it just pushes into a seal instead of bolting on like the older carbs did. This means that the carb has to be aligned correctly or an air leak can occur around the seal. The air filter assembly is what holds the carb. into the seal and aligns the carb.

If you haven't messed with the air filter assembly there is one other thing that I've seen cause this problem. Your bike has two vacuum operated devices on it. One is the VOES switch and the other is the fuel petcock. The VOES switch is part of th igniton system and the petcock is the fuel valve on the fuel tank. The vacuum comes from either the carb or the intake manifold and is routed to the devices by a vacuum hose. Make sure this hose in connected to all three locations and has no holes in it. The vacuum hose to the petcock is on the backside of the petcock and the VOES is located on the bottom of the frame top tube under the fuel tank near the carb.

I have seen the vacuum operated petcock cause a vacuum leak in at least one occasion. Normally, when they go bad they just shut the fuel off to the carb and the engine won't run. But, I did have one that caused a severe vacuum leak and the bike acted exactly like you're describing. I took the petcock out of the tank. Drain the fuel first, not easy to do with the petcock being vacuum operated. I got a large funnel and held it under the petcock while I slowly unscrewed it. Once you have the petcock out, you'll see four small screws on the back side of it where the vacuum hose connects. Remove the screws and check the diagraphm behind the plate. Be careful, there is a small spring behind the plate. Take the petcock apart carefully so you can remember how to properly reassemble it.

Personally, I would eliminate the vacuum operated petcock and replace it with a high quality manual operated petcock. Like I said earlier, if they malfunction they usually shut the fuel off to the engine. There you are, a full tank of fuel but none to the engine. I'd replace it with an original Harley unit for a 1995 or earlier bike or a high quality aftermarket unit like a Pingle.

You need to find this problem before you ride the bike too much. The lean mixture resulting from a vacuum leak will cause the engine to run very hot.

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