Yep, I have EXACTLY the same problem, it starts off OK, no real
hesitancy, then as the engine gets warmer, the problem gets worse.
I have changed spark plugs, the valves adjusted, oil changed, oil filter and air filter replaced over the last 6 months too....
The problem did go away for a couple of weeks after the spark plugs were changed, but it came back. So, it is booked into the my local garage to get the HT leads (spark wires) replaced next week. At the same time, I will also have the rotor arm and fuel filter replaced.....
Prices for the parts as below, just in case they are much better than the prices you get;
Distributor Rotor (BERU):
EVL 040 (0300.900.040)
Item No. EPS 1.406.119R
NOTE that the BERU rotor arm is fully compatible with the Bosch Distributor Cap.
Full set of HT Leads:
(For engine type AR16 202) were 61 GBP (12 GBP postage from UK to CZ) - NOTE that you would need to use the clips you have, and also use the Cylinder 1 sensor, as the leads do not come with these parts.
Let me know if you want links to the sellers........
I can't get on You Tube at work, it is a 'restricted area'.....