death46 wrote:Ahh cheers for explaining. Does the vacuum hose connect to the take-off point behind the frame or not then? I know exactly which nozzle you are talking about as it's that well concealed i only noticed it the other day.
About the faulty gasket, it was leaking anyhow and so surely that affects the vacuum effect of the fuel tank? My bike is definitely being starved of something, and i think it's petrol. As soon as the tap arrives i'll install it and see what happens from there,
thanks
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It fits to the one behind the frame thats well concealed.
The other 4 take-offs are usually blanked off by screws and washers... as long as they are not leaking air then all is good leaving them whatever way they are (if somebody has fitted the adapters that let you connect pipes to them make sure they don't leak air and are blanked off, you fit these when balaning carbs but usually remove them.)
Vaccum tap:
I'll explain how this works so you get an understanding.
The fuel tank and tap is a normal bog standard tank.. think of it as just a giant can with an on / off / reserve switch.
When 'On' you can empty out 3/4 of the tank... when in reserve you can empty out all the tank including the last 1/4 that you can't empty out when in On mode.
The only difference is the 'vaccumn' part.
Here you can see a picture of the diaphram inside the tap.
Even if you have your valve set to On or Reserve the diaphram (rubber disc in the picture) springs shut when the engine isnt running and closes the fuel off. This is a safety feature, so even if you leave the fuel turned 'on' and say your carbs spring a leak, the whole tank isn't going to empty itself.
When you crank the engine over it creates a vacuum (suck) to draw in petrol and air... the little vaccum pipe takes a small amount of this suction and pulls on the other side of the diaphram to suck it open, which so long as your tap is turned to on / reserve you'll get petrol comming out of the tap!
The problems with this system are.
1. Vaccum Hose
Over time the heat makes it brittle.. it can split / collapse / break off all together... if this becomes disconnected then you won't have any suction to open the diaphram in the tap and no fuel will flow and your bike will stop working! (i've had this happen at 70mph on a motorway! luckily my first point was to inspect the vaccum hose and see a big split had appeared! some electrical tape got me home till I could replace it!)
2. Diaphram
The diaphram in the tap is made of rubber. If it splits or perishes then either the tap will leak fuel out of the vaccum air nipple (the spare nipple on the tap.. this allows the sealed diaphram to move) or the fuel wont flow properly at all.
The hose is obviously cheaper and eaiser to repair.
If you have a busted diaphram you can mod the fuel tap to not use it (remember to turn fuel off when bike is not beign used as the safety feature will be bypassed)
http://www.akhara.com/nc30/fueltapmod/
You can read about it here on Mikes page.
If your diaphram is ok and it's just the vaccumn hose then make sure you replace that with proper good quality heat-reistatnt hose.
4mm inner diameter is good.. aquarium 'air' tubing gets too soft with heat. (i've tried) David Silvers sells Vaccumn hose cheap.