Stuttering while driving in rain

I have a 99 R1 and live in Bergen in Norway. The city with the most rain days on earth (the rumors say). Well anyway. If I drive in the rain, sometimes my engine start to studder at any RPM when giving gas. It gets over the stuttering and goes back to normal and drives well at that amount of gas. But if I want to give it even more gas it starts stuttering again and goes back to normal again. Sometimes its really bad and it almost has no power. This only happens in the rain. I asked a friend who has a 2001 model R1 and he said that water splashes around the excess fuel hose (the one that dumps excess fuel from the carburetors or something) might have a vacume and suck up some water drops and when water enters the engine it results in engine stutter. Did a full service a week ago, changed oil, spark plugs, cleaned the KN filter, syncro on the carburetors, so it should not be any of those things. PS had the problem before the service. Anybody got some good ideas? Any theory would be helpfull.

I would start by waterproofing all the loom connectors by applying dielectric/silicone grease. I suspect that your problem is caused by water/condensation somewhere, maybe the big white one on the LHS under the carbon infill.

Thanks, I will try that. Theres not been too much rain lately so haven't had the problem.

Your plug wires could be going bad and/or the coil connectors (contacts) could be providing a less than adequate connection (especially when wet). The possibility is that the water is allowing the electrical energy an easier path to ground than through the plug so you get the stumble.