Carb or Petcock Fuel Leak Question (Z750 Twin)

750steve wrote: Guys, quick question. Im not used to gravity feed fuel taps that we have on our bikes at all so i was just wondering if they are left in the 'on' position should there be some fuel leakage? Im finding some fuel build up under the carbs in the oil pressure sensor area.

If thats not the petcock what might it be??

my petcock was leaking very slightly so i bought a kit which i thought covered all parts required until i took it apart and found the diaphragm valve in bits.
On searching for a part i contacted Jim at redlinecycles who informs me it's extremely difficult to stop petcocks leaking and although he has got the assy in stock he says it will only break again.
He suggested replacing the tap with another type. I'm still going to try another valve assy as i want to keep mine original..
but the crux of it is petcocks are unreliable and break regularly.. (well that's what i'm told)

Ok, so i left the petcock 'on' last night & the fuel thats escaping is only coming from the left carb float bowl ONLY (pic below)

Motorhead i don't know if the overflow tube is pressed in or not, are they usually on BS38's. When i left the bike last night & before i read your post the thought of a cracked bowl entered my head, but when the petcock is off there is NO leak so im a little confused

If there isn't a hose connected to the overflow nipple whereby discharge is routed to escape underneath the bike, then the discharge will of course drip from the nipple onto the area underneath the nipple.

From the pic showing no hose connected, would suspect that the overflow fuel discharge is resulting from a leaking float valve.

Carb appears dirty inside, and float valve may be suffering from the unclean condition.

Good Fortune!

There is a hose connected to that outlet & all other outlets. Thats the only pic i could find to show where the leak is coming from, when a hose is attached the leak goes to the floor......without a hose attached it goes below the carb.

Remember though then the petcock is turned off there is NO leak

750steve wrote: Guys, quick question. Im not used to gravity feed fuel taps that we have on our bikes at all so i was just wondering if they are left in the 'on' position should there be some fuel leakage? Im finding some fuel build up under the carbs in the oil pressure sensor area.
If thats not the petcock what might it be??

750steve wrote: There is a hose connected to that outlet & all other outlets... when a hose is attached the leak goes to the floor......without a hose attached it goes below the carb.
Remember though then the petcock is turned off there is NO leak

Okay, so the originally reported Im finding some fuel build up under the carbs in the oil pressure sensor area is only when the hoses are not attached.

Remember though then the petcock is turned off there is NO leak -- As would be expected, because when the petcock is turned off, there is no gasoline available to leak through the float valve.

When gasoline leaks through the float valve, the fuel level inside the float bowl keeps rising until it gets high enough to escape through the overflow circuit.

Would suspect that the overflow fuel discharge is resulting from a leaking float valve.

Good Fortune!

Thank you Patton. So do i replace the needle only or the whole thing? Parts 39 & 40 from the diagram

Patton wrote: If there isn't a hose connected to the overflow nipple whereby discharge is routed to escape underneath the bike, then the discharge will of course drip from the nipple onto the area underneath the nipple.

+1 That's the overflow pipe, it needs a hose to take it down lower on the bike.

Has to be a leaky valve or improperly adjusted fuel height.

Count yourself lucky your petcock will cut it off: mine got bad enough to where the petcock leaked significantly and I had to run the overflow tubes into a bottle to collect the gas. I had to buy a new petcock assy and also fix the carb needle valves.

750steve wrote: Thank you Patton. So do i replace the needle only or the whole thing? Parts 39 & 40 from the diagram

Needle and the brass seat it mates with. Should be in any decent rebuild kit. Keyster makes a good kit for these carbs. The drawing shows both pieces as #40.

If you live in a country that has Ethanol (Alcohol) in the gasoline, read this:

Ethanol In Gasoline Problems (E-10,E-15,E-20 &E-85)

Certain materials commonly used with gasoline may be incompatible with high-level ethanol blends, causing them to degrade and contaminate the fuel. Metals that have been shown to degrade over time in the presence of high-level alcohol blends include brass,(floats & jets) lead, zinc(carb bodies) and lead-based solder.

Nonmetallic materials that degrade when in contact with ethanol include natural rubber, polyurethane, cork gasket material, leather, polyvinyl chloride (PVC) polyamides, and certain thermoplastic or thermoset polymers.

On the other hand, unplated steel, nickel-plated steel, stainless steel, black iron and bronze have shown resistance to ethanol corrosion, with nonmetallic materials like reinforced fiberglass, Buna-N, Neoprene rubber, polypropylene, nitrile rubber, Viton and Teflon meeting acceptable usage standards with E85.

1. Ethanol can break down resins and fillers in fiberglass gas tanks, causing them to leak.

2. Resins leached from fiberglass tanks can go through the fuel system, sticking to valves and other internal engine parts.

3.These deposits have caused bent pushrods and have clogged intake valves.

4.The alcohol attracts water, leading to increased corrosion in metal gas tanks.

5.Water in the fuel affects the octane and leads to knocking and decreased performance.

6.Ethanol acts as an efficient solvent, gradually cleaning out the accumulated gunk in fuel tanks and lines, and clogging carburetors.

7. Certain rubber gaskets and fuel lines are weakened by ethanol. Some rubber fuel lines may develop internal swelling, restricting the flow of gasoline. My understanding is the Silicone fuel lines resist the effects of Ethanol in gas.

8. The Ethanol in the gas has been reported to attack the glue used in gas filters, rendering them useless, as the paper filter medium is now coated with glue. It also softened the filter hose connection ends, causing possible failure.

As known, the "float valve" consists of a needle and seat.

Some carbs have removable/replaceable seats, while on others the seats are more permanently installed (pressed-in fit).

Before replacing the float valve, would consider thoroughly cleaning both the existing seat (especially the seat orifice) and the needle (especially the pointed tip).
If desired, may use a Q-tip chucked into a drill to help clean the orifice area in the seat.

And also examine the needle's pointed tip to assure it isn't worn (such as having a ridge), and isn't otherwise damaged.

If new parts are needed, kits are listed at Z1 Enterprises.

www.z1enterprises.com/detail.aspx?ID=299

www.z1enterprises.com/detail.aspx?ID=2087

As bountyhunter suggests, when the seat is separately available, both the needle and the seat should be simultaneously replaced, and considered as a matched pair, married for life.

Good Fortune!

www.loudfastugly.com/carbkits/carbkits.htm

This place has the Keyster rebuild kits I used on my 750 twin for $17 each. The kits are very complete, have all the parts.

I too have this same issue with the fuel leakage Patton you are a very knowedgable fellow thank you to all you guys here so far this site has been very informative and helpfull.BTW I am very new to the motorcycle world forgive me if i have a lot of questions.