Is it a vacuum fuel tap on a TZR, if so it could be passing fuel while standing and filling your crankcase with petrol hence it will not start. Got the same problem on my 350 YPVS at the moment.
Also bad starting can also be down to a leaking LHS crankseal which will pull in air and weaken the mixture, this is more unlikely as it will normally sieze pretty soon after.
Disconnect the fuel hose and put it in a jam jar to see if you get any fuel leaking out is the first thing I would try
Ian
also post here for a wealth of 2T info
http://www.yamaha-rd.com/forum/index...d165c1b50142ce
Threaded Mode