Couple of things you might do is check the jets in the solex's are still screwed in, and reset the idle mixture screws to make sure they are not massively over or under fueling the cylinders.
The jets in question are located under the cover on the top of the carbs and are brass I think with a slot for a straight end screw driver. Be sure not to over tighten or force as you may damage the slotted top. Idle mixture setting you should be able to find in your 18RG bible. Something like all the way in then 1 1/2 turns out.
Glen
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