GS850G leaking fuel at petcock.

[clagrow68]

I put a new petcock on my GS850G as the old one was super hard to turn and it was seeping just a small amount of fuel. I put a brand new one on and it seems to be doing the same thing. Just a slight amount if you run your finger over the edge where it bolts together.

 

[MaxPete]

Leaking petcocks are a real pain and the cause is usually the same - crummy quality parts regardless of which brand of bike they are on.

OEM valves were much better - but it is nearly impossible to get OEM valves now. So we have to use aftermarket hardware and they simply are not made to the same standard. The other issue is that gasoline has a very low viscosity (i.e. it is thin and "runny" compared to engine oil) and so it can leak past much smaller gaps or flaws in any components that are supposed to seal.

So - what to do?

I have found that the only thing that will really seal against gasoline is a gasket goo called Hylomar Blue. This stuff was developed by Rolls-Royce in the 1940s-50s for use in gas turbine aircraft engines and it is amazing. It never hardens and it seems to be impervious to anything.

The only issue is that auto parts places never seem to carry it - but you can buy it online from aircraft maintenance suppliers and a small tube is a lifetime supply for we motorcyclists. I just searched and found it online on Amazon for $17.35 / tube - as I said, a lifetime supply.

• https://www.amazon.ca/Hylomar-HMMS00C-040G-Universal-Blue/

Cheers,

Pete

 

[gold01ca]

Pete,

How would you use this in the petcock scenario?

Thanks,
Glen

 

[Nessism]

Where is the petcock leaking?

 

[Shin-Ken 1074]

With a new fuel tap you'd like to think the tap itself and the new O-Ring isn't the problem. Only two other options for fuel to leak, the flange or the bolts. Does the tank flange have only old paint or rust on the mating surface? If the flange is flat and not pitted a clean and polish of the tank flange should eliminate the flange as the leak. Sometimes fuel will leak past the tap bolts. To seal the bolts try using a fuel rated thread tape or fuel rated sealing paste like Hylomar Blue or Loctite 567.

 

[Nessism]

With a new fuel tap you'd like to think the tap itself and the new O-Ring isn't the problem. Only two other options for fuel to leak, the flange or the bolts. Does the tank flange have only old paint or rust on the mating surface? If the flange is flat and not pitted a clean and polish of the tank flange should eliminate the flange as the leak. Sometimes fuel will leak past the tap bolts. To seal the bolts try using a fuel rated thread tape or fuel rated sealing paste like Hylomar Blue or Loctite 567.

The screw washers have a rubber lip, so you don't need to fool around with sealing the screw with monkey snot.

 

[MaxPete]

I haven't started in on my "new to me" '79 GS850G just yet (still assembling parts - thanks Nessism !), but my old Yamaha XS650s have a fibre washer through which the petcock mounting screw goes. I always try to use a new washer each time I mount a petcock because they must fit the screw threads very tightly since the screws go up right into the tank (i.e. the mounting holes are not "blind" but poke up into the liquid gasoline in the tank).

Unfortunately, I have not been able to find those slick Suzuki washers with the rubber lip (p/n 09168-06023) as shown above in the Nessism post - but I have made a note of that part number.

Anyhow, good washers or not, if the washer does not seal tightly on the screw thread, the gas will simply trickle down the screw, past the screw head, and onto your hot engine or exhaust :hororr:. The other cause of a leak is petcock parts that are not quite flat - or a tank mounting flange that is slightly bulged out.

So, I usually put a thin film of Hylomar Blue on both sides of the fibre washer to help it seal - and I do not have leaks anymore.

The other place I have used it is to fix a leak on the body of the petcock itself - usually, because the "Chinesium" parts are not sufficiently flat - I have sealed those gaps with a thin layer of Hylomar Blue.

As noted earlier, this stuff never hardens and it is impervious to gasoline, oil, coolant,...whatever - so you can always disassemble the parts later - but they will not leak in-service.

Pete

 

[Peter#1266]

https://www.motorcyclespareswarehouse.com.au/products/fck-5-suzuki-petcock-repair-kit

 

[clagrow68]

Sorry I disappeared after posting. The leaking petcock was an aftermarket one from Amazon. And after careful investigating (me staring at it with a light and magnifying glass), It literally appears to be coming from the actual metal of the petcock. I can't see any crack at all and it just appears! Anyway, I put the stock back on after rebuilding it and it's fine. But, now on to the leaking carbs.

 

[gustovh]

I hope that you cleaned up the mating surface to the O ring on the diaphragm and that there is no thing but nice slick surface for the O ring to seat.

V