Hi Peter. The GCVs are prone to a couple of issues that don't happen to the OHV engines, but when in tune seem to run just about as well, which means very well.

Here are the instructions for adjusting the valve clearances:
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Remember, first, one of the cut-corners on GCV engines is that they don't have gaskets, they use RTV sealant instead. This means you have to be careful removing the valve cover: follow the directions, or you will end up with an old British cocked hat instead of a valve cover. Second, the special tool for adjusting the clearance is an ordinary tool - a Torx bit IIRC, but if not it's a hex key, nothing hard to come by. Third, the valve clearances: Inlet is 0.15 mm plus or minus 0.04, Exhaust is 0.2 mm plus or minus 0.04.

Maximum governed speed is 3,100 rpm, plus or minus 150. This is much the same as the GXV engines you are used to. To vary the speed, look at the left hand end of the governor spring. There are a couple of holes it can connect to, giving two different speeds. If you don't have a tachometer to check the speed, try both holes and choose the one that makes it sound more like the chondas you are used to:
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Please let us know if you have any concerns or issues, and we can try to work it out together, as usual.