My motorcycle engine gets relatively hot than it used to. Any suggestion to install a diy cooling system?

My motorcycle engine gets relatively hot than it used to. Any suggestion to install a diy cooling system? - 1

Added (1).
This is the BIke I have… Honda VT250F 1980s

Which bike? What kind of cooling system is the factory system?

If the engine is already liquid-cooled, make sure everything is working properly first

That really depends on the make and model of bike.

I'd do a diy service/tune instead and fix the actual problem instead of masking it.

Looks like you are racing it, I would have thought a bigger radiator or pair of radiators would do the job if they do not add too much weight.

Depends on a actual motorcycle- which is? As for a DIY cooling system? - again a actual motorcycle would vary. Old standard air cooled, new liquid cooled sports model, stock equipment or some silly noisemaker exhaust? Back to basics- clean the fins or the radiator, check oil level and type of oil, check the cooling stream for blockage. One old help- add a oil cooler and extra external filter, works on old dry sumps and the Honda 4s in racing or desert work got the external oil coolers and filters, helped a lot in street traffic also. Another little help for some with base cylinder gaskets- extra thick base gaskets to lower compression ratio, lots of Harleys and BMWs in the changover to unleaded fuels got this little help. Dirt bikes sometimes got a big starburst exhaust pipe nut with extra fins, factory would have them in a later model or as a racing extra option. A few dirt bikes got a exhaust pipe fins wrap- the hardware store door spring wrapped around first 4 to 6 inches of exhaust pipe, the plumber radiator fins around a 1.5 inch OD/36-37mm pipe would help some - mostly was for exhaust valve burnout with unlead fuels situation or racing, but sometimes used with a over wrapped and T fitting for a inlet to intake manifold preheater in winter.

The best 'diy' cooling system would be to figure out why its running hotter than it used to.

Do a complete coolant change for a start. Like Joe said, find the cause of the overheating, don't just try to fix the symptoms. One rough solution would be to remove the thermostat but this is not advisable.

Nice looking bike too

Look for worn water pump, clogged radiator fins, poor coolant quality, or low level, stuck thermostat, cooling fan not running, cooling system not bled of all air. (get manual to find how to check this - should buy a manual for any bike you ride)
Check for blown head gasket, lean mixture, timing incorrect (rare on modern bikes but still possible)
Give it a proper tune up & service (they're a lovely little engine but prone to chopping out bearings if oil not changed regularly enough
Is that your actual bike or just a photo? Looks like an aftermarket exhaust - this will affect tune & most likely make it run lean & hot

That's a water cooled engine. Is the radiator clean and allowing air to pass? Is the fan turning on when it gets hot? Then You need to check on your coolant level, then the thermostat and water pump.

It sounds like it has a cooling system that doesn't work that well anymore.