Hi guys,
Just got the bike MOT'ed for the first time in a year and now I have a little problem. After a short ride (long enough to get the bike warm) if I let the bike fall back to Idle its cuts out and wont start unless I hold the throttle wide open (and even then it only just about runs at idle speed with the throttle completely open). I thought it might have been because I routed the fuel line under the airbox next to the carbs and it might be getting hot and causing vapour lock so I re-routed it to where it should be on top of the airbox. Went out for a ride and the same thing happened.

So I wondered if perhaps the O-rings around the idle screws might be perished? Perhaps they're ok when they're cold but when the carbs warm up off of the hot engine the rubber expands and the gaps open up and it cuts out.

Before I go and change the O-rings does anybody have any other ideas? If that doesn't work I'm genuinely stumped.

Oh, and one other thing, the thermostat under the tank on the right hand side next to the coolant filler cap should have two wires coming out of it. Both of mine have been cut and a fan switch installed. Does this provide any other function then as a fan switch or is it ok that these are disconnected?

Cutting out when hot could be several things.

Failing coils
Over-fueling
Bad earth
Bad spark plugs



The thermostat (thermo-switch) has been bypassed by the sound of it which means your fan will only come on if you flick the switch. Slightly silly thing to do, if you forget to switch the fan on, the bike could overheat and possibly blow the head gasket (worst case scenario). I'd recommend replacing the stat (thermo-switch) and wiring it back up. By all means have a manual switch as well but connect it in parallel to the stat so you have the option to bring the fan on early.