Overheating 1991 Vfr750F ?

[Guest sleeping@65]

I have a 1991 VFR with close to 100K on it, and it has been a great bike. With that said, lately it has been overheating on 80 degree F. + days in traffic. It usually happens after 20 minutes of riding at 55-60mph. Once I start hitting lights at the end of my commute, the needle goes very high almost to the red and the bike seems hot (feels hot and starts shifting poorly).

* I have checked the thermostatic switch located in the radiator and it seems to be working properly.

* I have changed the thermostat as I suspected it was stuck. New thermostat didn't change anything.

* I have triple checked the radiator cap and yes... it is fully tightened.

The odd part is that I can see a temperature drop as I give it some throttle. The lower the RPM, the hotter she gets. So, my next thought is an internally damaged water pump?

The only other far fetched idea I have is that the bike is going too lean while I'm riding it. (I know the carb boots are old and hard and need replaced), but I just couldn't decide if this could be a possible cause. I'm tired of chasing my tail and I want my baby back Any ideas?

[Shinigami]

There are a myriad of reasons this can happen- clogged water passages in block or radiator, excessive glycol concentration, bad t-stat, air in the system, bad t-stat, oh, and, did I mention, bad t-stat.

Of course you already know that one. How's the coolant level in the overflow tank?

May I suggest you also post in the correct sub forum? This is the 8th gen forum. You might find a more specific answer in the right forum.

Cheers, hope you get a fast correct answer.

[V4 Rosso]

The odd part is that I can see a temperature drop as I give it some throttle. The lower the RPM, the hotter she gets. So, my next thought is an internally damaged water pump?

In that case I would suspect the charging system, not the water pump. You also did not mention the fan coming only that the fan switch works as is should, another indication that the temperature gauge is giving a false reading.

Btw, your's is third gen, not an eight' gen. On hot days (>25C) in slow traffic my third gen also runs hot with the fan kicking in regularly. Nature of the beast.