Yamaha DT80 Carburetor

Hello,

I currently own a 1993 Yamaha dt80, it ran smoothly until a few days ago it started reving itself out of no reason. I changed the throttle cable as the old one was sturdy, also i dissasembled the carburetor and cleaned it thoroughly, but found out the main jet inside it was tampered with (probably by the guy i bought the bike from), the top of the jet was reconstructed from tin and a hole with a smaller diameter was made, the reason for this i don't know, however i polished out all of that tin but the jet seems flimsy now. My question is does anybody know what type of jet do i have to buy to replace it?? It's a Mikuni carb, doesn't have anything written on it, except Q3 X3.

Also, any reason my spark gets all black and smokey? would i need an iridium spark?. The oil pump was cut off by the previous owner, so i make the fuel/oil mix myself, don't know why the pump was cut off, i've been running like this for about 3 months on it and it all went ok, should i do a check on it and enable it back again??

Would appreciate any kind of help on this