The most important thing is that there is a gap of at least what is specified, otherwise when the engine is hot the valves may not close fully, so causing the valve to burn and reduce performance.
Obviously there is not much that can be done with too wide a gap, as the adjustment is to grind the end of the valve! I’m my limited experience the valve lift is quite high so performance is less affected Though if tuning for performance you will have to fit new valves.
One issue with over gapped clearance is that many small engines have a decompression feature that involves lifting a valve ( usually the exhaust) to aid starting. Consequently an over gapped valve may reduce or nullify that feature. It is important when checking clearances that both valves are “ off cam”, particularly where a decompressor, which may be a “bulge” in the cam, is concerned; gap the valve when it’s still “on cam” and you will end up with a wide gap and an engine that snatches or kick back when starting is attempted.
In the absence of engine specific information, a good rule of thumb is that both clearances should be checked when the piston is a quarter of an inch down the bore AFTER top dead centre.
.
