in this condition i think you can tune the idle rpm to higher a bit (around 1k)  to compensate for the vibration during aircond on, for manual car i adjust this, not sure autos got any different.

Hi , anyone use those fuel injector cleaner before ? I saw it in the supermaket , plan to give it a try . Should I pour in the whole bottle to the fuel tank ? Or just a little proportion only ?

how's the result ?  Is it effective enough ?

It seems this starting difficulty is a characteristic  of Iswaras;
I experienced this even when the car was new.

1) Cold engine : Starts instantly when cranked.

2) Very hot engine (immediately after stopping) :
Starts instantly when cranked.

3) Warm engine : Need to crank about 3 to 5 seconds.

4) Immediately after engine run-on/dieseling occuring
at shut-off: Need to crank 5 or more seconds.

Pumping the petrol pedal does not seem to help.

So far I have not come across any explanation of this issue.

I believe it has to do with the interaction of following
in some way, and is not a symptom of some fault:

a) choke operation (air bleed for cold & hot state),
b) EGR (which operates after certain temperature),
c) remaining fuel clinging to the walls of the manifold, carb throat etc.
d) hot idle compensator air bleed,
e) petrol fumes inside the intake/carb.

Try floor the pedal when warm start.
step
1. turn key to on position.
2. floor the pedal
3. start the car.
4. after start release as fast as can, to prevent piston fly off.

caution to rpm meter, make sure engine run in safe range.

this advice from my friends that he had old iswara same engine as lmst. He said it is not a big deal, because actually the engine already started but just in low rpm like around 500 rpm which nearly same as the starter.

You could try checking the carburetor auto choke, maybe consider tuning it very slightly richer, do carburetor cleaning using threebond if you haven't done before.

Then on engine side, check valve seals and valve clearance.
Consider using thinner engine oils like w30/w40 fully synthetic especially from Lazada/Tesco/giant sales.
Remember to buy reputable brands from reputable sellers.

Make sure the spark plugs are at the correct heat rating, check if they are fouling or not.

Is the replaced distributor brand new original APM? if not, can consider replacing that.
Plug cables so long original Bougicord/Bosch, should be ok.
No comment on other aftermarket.

The starter you can consider a bigger one like from old Perdana, can consider recond.

Don't floor your pedal during starting, do light taps at most else you risk flooding the carburetor which would make your starting even more difficult.
The way you've explained, perhaps even your fuel lines may have clog or issues, maybe can check that as well.