1989 tw200 yamaha won't start

G'day egdbcs . Ok.now lets see.You say good spark,so i'm presuming you are doing the old sight test.Try bending the arm on a know good sparkplug about 5-6mm,earth the plug and kick'er in the guts(crank it over)Be very carefull , high voltage danger.If there's still a good spark it's safe to say that there will also be a good spark under pressure in the combustion chamber,speaking of which you should also do a compression test,anything over 100psi should be ok. as i'm not to sure of the extent of the re-build,hopefully the valves were lapped and checked for straight and true and valve seals replaced,if you notice oil on the tip of the spark plug you could have a leaking valve seal or oil seal .Try putting a small amount of fuel directly into the combustion chamber ,tighten up the spark plug ,install the plug cap and.......Yeah ..You guessed it ..."kicker in the guts".If all the abouve are correct and true it should fire up.If it runs for 5-10 seconds then stops you've got some sort of fuel starvation problem , could be dirt in the carb,blocked idle jet ,or air passage or even the needle could have come off it's clip,believe me with an old bike like yours anything could be worn and loose inside that carby.The only other thing to consider is the timing.There may be a good spark but is it happening at the right time inside the engine???. I'll leave it all in your capable hands EGDBCS.Hope this helps to solving your worries. Chow for now......Tilleydog..