How does the bike perform in your opinion?
Does it foul the plug?
If it isn't broke you might not want to fix it. Too rich is better than too lean. I don't have any experience with Montesa or trials bike jetting, but my guess would be your pilot is a little rich, or the needle taper for your riding style is a little rich.
My '04 has soot fouled the 6 heat range plug twice in the 6 weeks I've owned it, I ride in a small area so I don't get a chance to really clean it out. The performance off the bottom is good, so I'll live with the occational fouling. The fouling occured with 92 octane fuel, I just switched to 98 octane blend which may resolve the problem. Ran the first tank through it last night and there is a worth while increase throttle response and a definate decrease in the decel pinging which quiet's the exhaust note. Next gas run I'll blend to 100 octane.
My fuel screw is 2 3/4 turns out, the temp is 70* F, medium humidity, altitude is 440'.