Temporary lack of power

[Gnasher]

Could never understand why the pipes of the carb heater circuit weren't made wider?
Or is it something they corrected on later/other bikes?

They don't need to be any bigger, or they'd over heat the carb body.  Only a degree or so is required to stop icing any more and the mixture would start to evaporate.  They block mainly because owners don't use the correct anti freeze and/or mixture or none at all, by doing so will cause or encourage corrosion, which over time will block the the elbow.  Other causes are contaminated water, or if you're unlucky paint from the cooling internals can flake off and block them, I've seen this a few times in the past.  Golden rule, test your coolant every year for anti freeze % strength, you don't need to change it, just top it up with neat anti freeze if its lower or under strength.  The only time it's needs draining is when the engine been apart, they tell you to change it as they know most wont check it, it will reduce in strength over time and someone sells you something.  The coolant in my bike was 12 years old still working fine [size=78%]        [/size]