Fuel Tap

Opened garage door to be hit by a strong smell of petrol & a pool of petrol under the CB500.Walked over to the 500 had a look at the petrol switch to make sure i had not left it turned on,no petrol was running down the back of the switch ,so i drained the tank. Will have to the motor bike shop monday or tuesday to find out can i buy a repair kit to rebuild it or is it better to buy a new unit

krisstoffer allan wrote: to make sure i had not left it turned on...

Why turn the switch off? It's for this particular reason the switch is equipped with a vacuum-driven fallback-valve.

The second you shut off the engine, the vacuum-valve cuts the petrol feed. No need to turn the hand-operated valve off.

I read your text and gather you DO turn the manual valve off, right? This sparks two questions: Do you do this because otherwise you'd get the puddle of petrol? In that case, your vacuum-operated valve has been defunct all along. If you're just using the manual valve out of old habit - you might have worn it out?

I believe the switch assembly can be disassembled and that spareparts are available.

On removal from the tank, don't be surprised if the strainer is hard to get out. I broke mine, and a new one is not exactly cheap... Tip: Patience and - for lack of a better word - finesse is what you need to remove the strainer.

Diaphragm repair kits are available from places like Wemoto, but the only kit I could find for the on/off/res tap was from NRP. You have to drill out the rivets to get at the seals. NRP recommend tapping out the holes for the supplied screws, but I found there was room to fit nuts on slightly longer screws.
http://www.nrp-carbs.co.uk/shop/index.php?route=product/product&keyword=cb500&product_id=4384

I've not got so much confidence in the vacuum switch following my experiences. I picked my bike up as a non-runner that hadn't been taxed for 5 years. There was no petrol in the tank & I assumed the dregs had evaporated away over time. I realised I was wrong when I unscrewed the dipstick to a fountain of water-thin oil - all the fuel was in the sump! Now it could be that P.O.s repeated cranking of the engine & a stuck float valve was the cause, but some time after I had rebuilt the bike & got it back on the road, I had a few problems & checked the tap. Turned on, no fuel flowed. Sucked on vacuum pipe; fuel flowed. Stopped sucking; fuel still flowed! I couldn't see anything wrong with the rubber parts & the full Honda kit is quite expensive (part no.16953MY5B60), so I got a replacement fuel tap off ebay. Now, I turn the fuel off whenever I park the bike up for more than a few minutes. One advantage of this is I get frequent verification the tap works as I invariably forget & it starts spluttering a few hundred yards after setting off!
Are you sure the leak isn't from the union where the tap is fixed to the tank - possibly more likely than the tap itself?

I got a leak on the boss that the fuel tap screws on to; cured it with a can of Petseal which has long since disintegrated thanks
to ethanol in the fuel nowadays (there was a thread recently which mentions a sealant which is resistant to ethanol, @Badseeds knows about it)
First thing, remove the fuel tap and check the condition of the o-ring!

Doh! Must speed up my typing!