Pa help naman sa car trouble ko

car details
toyota corona carb
12r engine
Oil change, air filter change two weeks ago, fuel filter and high tensions wires changed about 6 months ago, Radiator flush and cleaned a month ago.

I took a a road trip up to laguna about a week ago around 90kms. Got home okay and engine was running okay. On weekends i make it a habit to check my spark plugs para makita kung malinis pa and okay naman ang lahat.

Today i made a short trip to SM around 20kms away wala naman problema, pero on the way home about half way napansin ko biglang naging 1300 menor ko pero ok pa naman andar pero pag naka stop at idle malakas ang menor at vibration ng engine. Got home okay then checked my spark plugs asap, they were all covered with dry black carbon and the tip of my muffler also had black carbon on it, i cleaned off the spark plugs and sprayed carb cleaner down the carb at naging okay naman ang andar at bumalik sa dati ang menor, di ko pa nata try sa long drive uli at baka tumirik, ano po kaya problem ng car ko? TIA