I went to start the Trophy today so I could move it and it wouldn't start. I got a strong smell of fuel so thought it wasn't sparking. On further investigation the half gallon of fuel I had put in the other day had vanished. No sign of a leak so I checked the sump and sure enough that's where the fuel had gone. Now as I understand it there is no "off" position on the fuel tap and that the vacuum shut off should stop fuel flowing, as should the needle valves in the carbs. I'm assuming I had the tank switched to prime instead of reserve which would account for the fuel getting to the carbs unabated but surely it should get no further unless the needle seats are bad? Can anyone confirm that the positions for the fuel tap are up for prime, pointing back for on and down for reserve? also are the needle seats replaceable on Mikuni carbs? Thanks in advance. Ps the bike is a 92 900.
If this is the petcock that you have, you can read the positions in the image. I just did a google search for images of the fuel petcock, but I'm not certain that it's for your year. You could try the same until you find your specific petcock, or spend a few bucks on a manual. https://haynes.com/en-us/triumph/trophy/1991-2003
Hi Fuel tap positions depend on year all of mine built, late 92, 94 & 99 are pointer up 12 oclock = Prime Pointer @ 3 oclock = ON Pointer down @ 6 oclock = Reserve Some earlier ones the pointer was set in a different position Forward / Up / Rear Vacuum should shut off the tap @ On & Reserve. Prime leaves the fuel feed on gravity feed I suspect you have dirt / grit under one of the float valve/s tips leaving fuel to flood into the cylinder/s. Float valve needles are available, but I think on the Mikuni's the valve seat is part of the float assembly, but, I could be wrong abot that ........... wouldn't be the first time.
Have a chat with Sprint mfg for the needles and advice, https://www.triumphparts.gbr.cc/product.php/7004603/ Can confirm oldyam, ie fuel tap position and the pic of the tap (hackdriver) is not the standard tap for your model, but who knows what has been fitted in the past. If you need a workshop manual for your bike here is a link https://www.dropbox.com/s/ia2hex5rw70pip4/Triumph T300 Service Manual.pdf?dl=0 and if its any use https://www.dropbox.com/s/a67oymz7es51402/Triumph T300 Owners Handbook.pdf?dl=0