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