drilling a wall with guttless hammer drill would be about right. It may not be that serious but i just thought it wierd that it would just sort of kick in at these revs, it seems to disappear after about 6200. the whole engine was balanced incuding the flywheel and clutch. after 1000 kms i had the engine tuned up on a dyno that cost me $350 so i don't want to start messing around with the timing.

perhaps i am a bit paranoid. but its good to get these other ideas.

Don't worry about it then. If it is balanced it should be fine. Just remember as mentioned previously.It is a 4 cylinder engine.They are not that smooth.These engines are 70's design.Even with balancing they still have little vibrations due to no counter weights. Couple of months ago I went for a spin in a A14 bakkie. Was also balanced and sidedrafts.Made alot of noise on the carbs but that's not the point. It also had a smooth vibration up to 7000rpm.
Nothing major, just a small smooth vibration.

drop by one day when im home Jeff. When the blue 60 series cruiser is out the front, im home. I'll put my 3rd year apprentice mechanic ear to it