My 1974 Yamaha 250 Enduro wont start I have cleaned and redone the carb. I have changed the coil pack and spark plug. Any suggestions will help Im not a mechanic by any means so not sure where to start next.

You need good compression ( at least 90 psi , kicking it with the throttle open) , good crankshaft seals for sucking the fuel/air into the botton end, proper point gap and timing set for spark ( spark should be big and fat,if not the source coil is weak,, this is a flywheel magnito ignition and it needs no battery to fire the plug) if you clean the carb, make sure you also clean the choke pickup tube or it wont choke. also make sure you have the slide installed in the right direction ( not backwards and the idle is not set too high at first...compression/****-good spark at the right time-proper fuel/air ratio and it will run

Does your bike have a battery? lot of the older bikes with battery and kick start need the battery to excite the ignition untill bike is running.

Are the points at the required gap,check wire from points to coil.the plug lead can break down and track to earth,with plug body earth see if you get a spark at the plug,if not,check coil,wires in ignition lay out,and ignition switch.

CK air filter,if it has one. If your getting spark and fuel it should start. I worked on a carb. for about a week cleaning etc. no luck, finally took it to a real mechanic, he cleaned the carb and it ran the next day. Don't bang your head against the wall it cost a few bucks (really few) but worth it. I'm no mechanic.