If the speed excursions happen at 2,000 rpm, you should try to cure them by adjusting your idle mixture. They don't matter anyway, but since you have an idle mixture adjustment, this sounds like a good time to try to get some benefit from it.
Honda's idle specification is 2,000 rpm plus or minus 150 rpm, so if the speed it is running at is within that range (ignoring the odd stumble) that is satisfactory - but the speed may vary a bit when you adjust the idle. Remember, the instructions say start with the screw at three turns, and see if you can make the idle speed increase by adjusting the mixture. If you can, then back off the idle speed screw to get back to 2,000 then try the mixture screw again to try to get it to run a bit faster. Repeat the process until you've found the mixture that gives the fastest idle, and the speed screw adjustment that gives 2,000 rpm with that mixture setting.
If it makes you feel any better, classic Briggs engines do those occasional speed changes too - and they don't have an idle mixture adjustment that might cure it. Each time it does a speed twitch though, the crankshaft position (frozen by the stroboscope) seems to only move a fraction of a turn. You just keep telling yourself "OK, this isn't a car engine. You can't expect much." (And having said that, before Port Fuel Injection, car engines didn't idle all that well either.)
