250-500cc petcock rubber o ring - what's the trick?

Hi fellow husky riders. I noticed a fuel leak from the petcock after my last race. I've removed it and cleaned away the crud that was built up but now when I try and tighten up the petcock to the tank the rubber o ring/washer keeps moving/squashing out of one side as I tighten the two screws up. I wouldn't even say I'm over tightening them screws before the washer pushes out.. any help much appreciated! I'm on a 2008 wr250 if that helps.

Thanks in advance

Myles

I'm not sure what's going on there. It might help to have all traces of gas/oil mix removed from the o-ring and its seating areas--it might be lubricated to the point that it's too slippery to stay put under force. If that doesn't work, inspect the seating area for the o-ring carefully--any damage there? If all looks good, then it might be worth just trying a new o-ring.

Thanks dfeckel, I'd not even thought about it being covered in petrol.. Will dry it off and try again!

I replaced my whole petcock, it wasn't that much

I've been trying to find a replacement one but nothing in the UK it seems. Where do you get yours from?. I'm happy to go universal with a replacement one. Was surprised how basic the set up was.. cheap plastic thread formed from the tank that the petcock screws on to. Was expecting a filter type petcock but mine just has a little straw tube.. Will post a picture in a minute as someone might say I've not got the right o ring or even petcock.

Here is what was happening to the o ring. Have dried it of and tried again and appears better seated

Here is the petcock and o ring... does this look normal to everyone? I noticed the screws were already a bit chewed so I suspect the last owner had a similar leak issue. Possibly of home made repair so always good to get some expert advise!

in picture 3 look at the threads inside the petcock at the tube, there should be a screen that's shaped like a tube
I bought mine at my local dealer OEM part

Thanks.. I wondered whether something was missing as all the photos I've seen have a kind of filter looking thing which I guess the straw tube goes in.. off to my local dealer tomorrow.. hopefully they are still accepting that the WR exists rather than the all new ktm/husqvarna range!

Thanks again for your help/advice

Plenty that fit on ebay ! Or just pop into Halfords and purchace a huge box of assorted o-rings.
http://www.ebay.co.uk/itm/Uprated-H...41?pt=UK_Motorcycle_Parts&hash=item256119793d

http://www.ebay.co.uk/itm/New-OMG-S...76?pt=UK_Motorcycle_Parts&hash=item25611aaba0

Nice one community - will see how I get on but very handy to know there are alternatives available.

Update - bit of drying out of the o ring and using a flat head screwdriver to hold the o ring in place and bingo, dry petcock.. need to ride it and make sure it holds but so far so good. Cheers for all the advise.

It may be that the oring isn't the correct one. It looks a little fat to me.
Hylomar gasket sealer works good for holding o rings in place and is completely fuel resistant.