Hi.

My F3 bike starts up fine from cold every time with a little choke.
Depending on the weather temperature, the engine will lose the ability to do high revs and slowly die, after 2-5 minutes. In warm temperature it goes quick, in cold weather it takes longer.
After it has stopped I have to wait around 5 minutes before I can start the engine again, and thereafter it runs flawlessly. I never have these problems with a warm engine.
So, to sum up: Starts from cold, stops after a while, have to wait and then starts and runs with no problems.

I have tried carb cleaner with no difference. Radiator flush gave me 4 runs without the problem, but it did come back and is there every time.
I have replaced both the thermostat and the thermo valve (connecting the carb with cooling system) with no luck.
I have tried having the gas cap open while starting up, in case it was a vent problem, but also with no luck.

As I am running out of ideas I hope to get some inspiration from you guys 

Br. Rasmus

 

sounds like the starting procedures for an airplane when cold..

with that, you crank the engine a couple of times, leave it, and then after pre-flights are done, start it..it has to do with the fuel not being able to readily vaporize when cold..it might just be a coincidence and you actually have something wrong..but when you are saying cold...how cold is it?

 

Hi.

Thank you for your reply.
Beeing cold is like 10-15 degree Celsius, equals 50-59 degree Fahrenheit.
On a summer day (25-30 degree Celsius) there is never a problem.

Br. Rasmus

 

Could be fuel pump. Think about it, it starts fine and runs for a few minutes then dies. Like when you forget to turn on your gas tap. After some heat soak, the fuel pump works fine and the bike runs great. Check your contacts to the fuel pump for corrosion or wiring issues. Sometimes the contacts inside the pump need to be replaced. There is a thread for that here.

 

its currently 10 degrees c here in the uk according to my weather app with wind we are talking less especially over night so probably just cold, my hornet 600 does the same it starts revs up to about 3k then slowly dies put the choke on and it starts up easily and will rev through once the choke is taken off after a minute or so.

but if your still worried check and clean-
fuel pump
carbs
fuel lines

replace your spark plugs and make sure your exhaust isnt blowing then as a last resort go to a dyno and get a read out of the air:fuel ratio

 

Sorry for the delay in relying to this thread. I am now the proud father to a son and he takes more time to get running than my cbr :-)
Anyway I took your advice and replaced the point switch in the fuel pump (this can be done with pump still attached to bike/fuellines).
Best 20£ I ever spend.
It really solved the problem and this bike runs better than ever.
Thanks again for some great advice.