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Have owned two R80's over the last 30 years, one twin shock the other mono. Both had a single throttle cable to a junction box under the tank then separate cables to each carb, never any problem.
My recently acquired R100R has two cables from twist grip to carbs. and are proving to be a pain due to there close proximity to the large instrument panel fitted to this model and resultant tightish bend. Wonder if anyone has had problems with this model or the R80R.
Am contemplating converting to a single cable and junction box.

You,are not alone. I have owned my R100R for 24 years & always struggle with those cables & seating the cable at retention lug under the Master cylinder. Not sure of the original routing, but the way I have them at present, they don't bind, and RPM doesn't increase when handlebars are turned, so its happy and so am Iat the moment. Choke has single cable/splitter box. (204,000km. Rear main seal, Valves, guides, rings, starter motor replaced. Final drive & gearbox rebuilt. Keep an eye on your paralever pivot bearings. Fitted TriSpark ignition last year. It has been good so far. Just rebuilt carbies & trying to resolve white plug tips before 6,000km trip in August. Process of elimination).

This is my temporary bodge to prove a point. it keeps both cables together and held tight into the twistgrip body with a cable tie. Its worked for 100 miles and has enabled me to balance the carburettors.
I think the best solution is to convert to a single cable with a bit more length and a splitter.
This is my first acquaintance with an R100, so much more grunt than an R80.