Help please

[FA50 rider]

my nut that goes on top of the valve haed does NOT go on all the way on so the nuts not geting enough thread and keeps coming lose, i need to know what to do to fix it, its an 1982 yamaha XT250 and has any body got a manual for one, have a look at the pic

[Colapop]

Check in the "General Maintenance" forum for a manual here (http://www.kiwibiker.co.nz/forums/showthread.php?t=10556).

[Paul in NZ]

Do you mean you can't wind the valve adjuster in far enough to get the correct clearance? If thats the case - something reasonably serious is wrong.