I have more things to check/change before I come to a conclusion, I ll keep this thread up-to-date, maybe someone experiences the same issue in the future.
Today I got my TPS replaced and guess what...It feels like riding a totally different bike.
Rides smooth, good throttle response, no petrol smell, no hiccups, no engine stalling, stable idle.
I asked the people from Yamaha garage to listen the engine sound for valve noise. They said that it sounds mechanically perfect and its probably not necessary (however, it is not enough to diagnose bad valve clearances only from sound, but since the cold start is instant, I assume its not too bad).
I asked for a rough estimate on throttle bodies adjustment price, and they answered about £30-£35... which I think is a really good price. Its less expensive than buying something like that: http://www.carbtune.com/
and do it my self.
For the time being the bike rides great, but I am goind anyway to do the followings:
- Use the other half of the Seafoam bottle on a full tank.
- Replace air filter
- After the Seafoam/Petrol is consumed, I 'll change oil+oil filter
- Measure Valve clearances (just to know their state and for educational purposes )
- Do the throttle-bodies adjustment at the Yamaha service point I mentioned before.