If you want carb overhaul, go to kamuning district in QC, madami duon carb shops, mura lang overhaul (I paid P500 for labor about one and a half years ago). Dali lang iyon, it will only a few hours. Just buy the carb overhaul kit that they tell you. Don't try to overhaul the carb yourself since dami iyon small parts which can get lost. Leave it to the experts.

I suggest you do the carb overhaul and engine overhaul to fix everything. Hirap naman if after overhauling your engine it doesn't run well because of worn or dirty carbs.

And considering the age of your engine, I suggest you do the full engine overhaul - baba ang engine. That way you just spend once on the overhauling gasket set and labor. Mahal din ang gasket set and labor.

If the cylinder clearance is already big, install cylinder liners to put the bores back to standard clearance - you may not have to replace the pistons if they are not worn.

Also replace all the valves, valve guides, valve springs, valve seats, bearings, etc. After that your engine is as good as new. And get a good machine shop to do the machining. Expect to spend P5T+ for the machine shop alone - machine the heads, crankshaft, and the block. You probably wont have to replace the oil pump, it hardly gets worn out.

I've done several overhauls before and the results are always good as long as you don't skimp too much on parts and machining. Remember the motto - do it right the first time and you'll have an engine good for another 100,000km or more.