Hey! 4AGE experts need help about my car it's a Toyota Starlet (KP62) with a transplated 4age Hi Horse engine.

I have an idling problem, which is kapag mainit na yung makina consistent yung pag taas, baba nung RPM. Besides mejo "putok putok" yung idling nya. I noticed it lalo naka free flow muffler ako.. Nagpalit ako ng distributor cap since i thought sira yung distributor cap pero ganun pa rin..
also i've noticed na regarding the spark plugs parang di maganda yung sunog nya...laging maitim yung tip when i cleaned it nagiging ok yung idling but in a long run...bumabalik na nman yung skit nya...do it needs a top overhaul for the engine or baka may problem din sa intake manifold, distributor or alternator??

Need help guys...

Thanks.

More power Tsikot.