Rough running when cold

So I'm finding my SF is running badly until it's fully warmed up. When you start it it can back fire and die. Lots of pops and bangs when cold. When you ride it it's juddering when you keep a constant throttle. Once it's warmed up it all smooths out and runs like it always has. This started happening last year. Before that it was smooth while warming up.

Bike has had relays replaced with Honda ones, replaced the cam sensor, injectors and coil for Bosch. Temp sensor is Replaced the HT leads for Magnecor, fitted NGK iridium spark plugs and lambda sensor eliminators.

Any thoughts?

Sounds like the inlet air temp sensor is faulty and showing a high temp which gives a weak mixture until the actual temp matches the sensor. Just because you have replaced it does not mean the new one is any good.

kommando said:

Sounds like the inlet air temp sensor is faulty and showing a high temp which gives a weak mixture until the actual temp matches the sensor. Just because you have replaced it does not mean the new one is any good.

Click to expand...

I have a Bosch one i can try swapping it for to see if it makes a difference.

Maybe it’s worth checking the operation of the IAC valve which is underneath the throttle bodies.

kommando said:

Sounds like the inlet air temp sensor is faulty and showing a high temp which gives a weak mixture until the actual temp matches the sensor. Just because you have replaced it does not mean the new one is any good.

Click to expand...

Both the air temp and head temp sensors can be tested with an ohm meter and little heat applied.

Mine has always run a bit rough when cold but never quite to that extent. The head temp sensor changed spec from the earlier to later - there have been discussions before on this. I always start by swapping sensors - saves time in the long run. Do you keep the bike on a trickle charger? If my bike is reluctant to start when it does it can be really rough and I believe its because the lower battery voltage when cranking messes up the sensor readings....

I've replaced the head temp sensor and it's back to it's old self. Well seems to be.

Thanks for the help!