CB900F exaust pipes temperature difference. Why?

[flexgrip]

Ok, guys, the motorcycle is CB900F 2002. This is not my bike, I am choosing which to buy. And this is the second CB900F (each from different people) which demonstates the same situation exactly with the fourth cylinder: fourth cylinder seems to produce two times lower gas temperature comparing to other cylinders - https://youtu.be/GIhHovQIkyM

Video was shooted 10 minutes after engine start.
So may be it is normal? You can hear the running engine sound, for me it does not produce any suspicious noises. What is your opinion about sound?
Pyrometer was tested on CB400 after this video was shooted and all cylinders indicate approx. the same temperature.

So the questions arise:
1. Is temp diff normal?
2. Is engine sound ok?
3. If not - which problems could indicate this situation?

[jaffa90]

Is it a carb / fuel injection / water cooled model???
Hotter pipes are a weaker mixture or cooler pipes too rich.

[flexgrip]

[jaffa90]

I suggest that the injectors and fuel rail need cleaning & testing first before any other adjustment.

[Kawasaki Jimbo]

I think it might be to do with differences in the the surface areas of the measurement spot. The laser pointer only indicates the centre, and the measured area will be larger the further you are from the surface. I'm not sure if that would over- or under-estimate the temperature, but your data suggests further away (larger measurement circle) biases it upwards. Take readings from the other side of the bike and I reckon the story might be reversed.

Edit: cylinder 1 first pass = 227C, ten seconds later it's 150C. Suggests measurement error.

[Islander]

[Octapode]

That could be a result of the surface of the exhaust pipes too. Shiny surfaces reflect IR from the surroundings and have emission characteristics the thermometer probably isn't set up to work with, which can cause all kinds of weird readings. It can make for cool pictures with a thermal camera though.

[jaffa90]

At the end of the day the spark plugs colours will tell all about the fuel mixtures.
Carbs or fuel injectors/pipes need cleaning before any further adjustment.
16 years old and all.

[ThatDippyTwat]

[CChapin]

I have an 82 Cb900f and have the opportunity to buy an 81 engine that appears to not be burning oil like mine does. Is there a difference between the 82 and 81 models engines?

[mentalboy]