Your avatar looks like a CB500K3 - which as Bryan says, they had in some European countries (but not here)
WRT to misfiring in the wet - a common problem I'm afraid.
You'll need to go over the plug cap / HT lead joint very carefully. If in doubt, replace plug cap and snip 1/4" off the end of the lead before screwing in the new one.
The other place that suffers from water ingress is the joint between the HT lead and the ignition coil. This faces forwards (under the tank) and collects all the wet thrown up from the road. In the past I have wrapped clingfilm around the offending area for a short-term fix. In the long run, remove the coils and treat the area with RTV (Room Temp Vulcanising) rubber sealers after first roughening up the surface of the coil.
Others have replaced the coils with either modern stuff (eg CBR600) - but may need to fabricate bracket, or those from the DOHC CB750/900 which have removeable HT leads.