I suddenly started having problems with my RPMs dropping too much when I pull in the clutch lever. E.g. I arrive at the lights, pull in the clutch, the RPMs temporarily drop to about 300, and the bike either stalls or the RPMs climb back up to about 800-900 where they remain. I’m not sure if it’s just a coincidence, but this started happening the next day after I took the bike out in the recent 40C heatwave(no issues at all during that day).
Sorry but isn’t 8/900 a bit low? Should idle between 1000/1200 usually.
Adjust idle, ride a bit (not in traffic) and se how it goes. If still trouble needs a mechanic.
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Assuming the motorcycle is in gear when this happens the root cause will be clutch related. The clutch is not fully disengaging causing the engine to labour, resulting in a slow idle and eventually stalling. Since the fault started following the recent heatwave I’d suspect it to be a clutch adjustment or fluids issue. Depending if the clutch is cable or hydraulic some things to check include:
Clutch cable and lever free play
Engine oil viscosity and condition (10W-30 will struggle at +30°C, 10W-40 will be good to 40°C)
Clutch fluid condition and moisture content
Coolant level if water cooled.
If I was a gambling man I’d wager the fault will go away with the heatwave but its never a bad idea to have a closer look at the likes of engine oil viscosity, clutch fluid replacement and the condition of the coolant. Clutch fluid and coolant replacement are probably the two most neglected items in a service schedule.
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I agree, clutch is dragging. adjust your cable/lever first.
Can you push it ok when it’s turned off and not in gear?
It is indeed. Mine normally idles around 1100.
Is there anything you don’t know, @National_Treasure? 
The next time I rode the idle RPM actually went up to 1500-2000 (maybe because I gave the throttle the beans when I started the bike up which I don’t normally do). But has since gone down to the normal 1100 and no longer drops or stalls in the last few rides.
Nonetheless, gotta be honest, I haven’t changed the clutch fluid in at least 5 years, so that’s something I will definitely be doing right after I resolve the water pump issue. The coolant has been renewed recently, but the water pump has developed a slow leak so I’ve ordered up some seals to replace.
I sometimes feel my teenage years spent in apprenticeships were a waste of time since I found ‘selling coals to Newcastle’ far more lucrative but it has stood me in good stead to service and maintain my own vehicles ever since.
I’m glad I can benefit from your apprenticeships as well 
Just a question: your bike is carbed or injected?
Injected.
Ok. Not sure how your bike works, but mine has two possible causes for rpm problems at idle: TPS (throttle position sensor) and/or ISC (iddle speed controller) unadjustment. In my bike you can force adaptation to climate variations (temperature and pressure of air) so that these systems provide valid inputs to the ECU. Sorry for the long explanation, maybe your bike works differently. In case forced adaptation doesn’t fix the problem, you need to plug the bike to a computer.
RPM’s vs clutch engaged/disengaged is clearly a clutch friction plate issue, nothing to do with the throttle position sensor, idle air control valve, manifold absolute pressure sensor, or any other component of the fuel system.
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Absolutely, if that only takes place when pulling the clutch, the most probable cause is what you pointed
@Alighieri thanks for trying to help, but if you see the last few messages, the issue has been resolved. It was just the aftereffects of the heatwave.
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