TOPIC:

With how you describe it I would presume that it is running retarded which will make it very low on torque in the bottom end but a bir more lively in the top end. You will need to correct the ignition timing but I don't consider that it will be the root of the overheating.

With the very slow to cool it says to me that there is not enough flow through the radiator.

You probably have already done much of this but some suggestions.

When the engine is cold the coolant is bypassed through a tube and not through the radiator so the engine heats up more evenly and as it heats the trermostat opens to let the coolant flow through the radiator and also blocks off the bypass. to do this the thermostat needs to be the correct length, even 3mm short and you get half the coolant through the bypass. did you make sure the thermostat was the correct length and did you inspect the seat of the bypass cutoff valve to be sure it doesn't leak.

I have seen the same problem of the slightly short thermostat on the BMW K series bikes and it drives men mad.

Also when you let a radiator dry out often the coolant that is in the crevices will crystalize and grow which can restrict the flow, the crystals dont disolve easily and can cause ongoing problems. I came across it in the early 70s with the water cooled Suzukis but havent seen it in the last 20 years so the formulas have probably changed. Did you clean the fins on the outside as they collect an amazing array of cooked bugs and if the fork seals leak the oil can get into the fins and collect dust.

Something that came to me just now. Are you sure your fan is wired correctly? If you reverse the phase your fan will blow out rather than suck in. Imagine how shitty this will work when you have air coming towards the bike at speed and the fan is trying to fight it?

That being said, at highway speeds even in 30C heat my fan doesn't come on at all unless I'm really pushing it.

You could also try water wetter. I used it on my 300 HP ZX12R which would always overheat in traffic because it wasn't built for that. It helped greatly. You shouldn't have to use it in stock form unless something is messed up elsewhere but it will help you run cooler regardless.

www.redlineoil.com/product.aspx?pid=74

I've heard lot of good things about water wetter but haven't tried it personally.

Something to consider for those interested is using polyethylene glycol in place of ethylene glycol. The boiling point of a 50/50 mixture is 20 -30 degrees higher than the ethylene glycol. In the event of a near overheat issue, the polyethylene glycol will not boil in the critical areas which is around the head gasket and exhaust valve passage. The steam bubbles act as an insulator and not transfer heat which creates hot spots which are destructive.

I might switch over to the polyethylene glycol this winter. I've not had a heat problem but an ounce of prevention is worth a pound of cure. That in conjunction with water wetter would make a big difference in heavy traffic.

Thanks again, you are a fountain of information.

Ive checked the fan and it's blowing the direction it should, the rad was flushed through and externally is not jammed up with bugs etc.
Is there a way to check the stat is working? I guess the bypass pipe should be hot while the rad is cool until the stat opens.
Is there any advantage with the 7 blade fan? Or won't it make much difference?
Just another idea to try and cool things down, especially with our hot summers.
Btw, I've just ordered from ebay a bottle of water wetter.

Yes a seven bladed fan will help, as will the water wetter but I still think there is another issue at work. At what point on the gauge does the fan kick on? Halfway? 3/4?

Have you tried a manual fan switch? Turn the fan on earlier, like when driving in heavy traffic. Don't let the motor get a chance to reach the point of overheating.

Mine wasn't overheating but I put a switch in anyways. I do with all my bikes. Whenever I am in traffic or see the needle crawl to the 1//2 way mark I turn on the fan before the thermostat does. As a result my temp gauge never goes much over half.