Hi, my 1986 Kawasaki KX80 is easy to shift in the first and second gear, but the third, forth, fifth and six gear are really hard to shift in. I'm guessing that it's the timing that probably needs to be adjusted but I don't know how? I could really use anybody's help please.

Thanks!

Are you using your clutch to shift

First check you have the correct oil level in your gearbox. Some people think putting 2 stroke oil in the bike oils everything. If the oil level is low/empty, your may have warped the gear selector forks. If so they will need replacing.