1984 Nissan Truck Timing?

I am part of a majority that is having alot of trouble timing my nissan pickup, the previous owner messed with it alot, lately it's been running worse and everyone i've talked to says I need to time it so I say ok help me out they pop the hood and look under it and say sorry, there's no timing mark I can see or anyone else for that matter all the stickers from under the hood are gone I am lost I love this truck it's my driver I depend on it frequently but it's just been running so poorly I can't go up a hill faster than 15mph it still has the stock carburetor and lately it's started missing so if you could help me at all i'd appreciate it I really don't want to send this thing to the scrapyard or spend a zillion bucks to fix it