[Steve O]

Since you undoubtedly are running a thermostat, I would question the accuracy or the gauge in the dash. It is simple to check if you have access to a pyrometer, (either the infrared kind or the older thermocouple probe kind will do.) You get the engine warmed-up, and then take a temp reading in a couple strategic locations, i.e., the thermostat housing (which is the outlet on the intake manifold where the upper radiator hose is attached), center of the top of the cylinder head, top of the radiator, etc. Any auto repair shop, and most well-equipped shade tree home mechanics will have a pyrometer these days, and taking a few readings should take all of about one minute.
If you find the temp readings are consistent with the gauge readings, then I would replace your (screw-in type) thermostat, which is the same as twin-carbed 105s like the Duetto. If the pyrometer readings are a more normal 160-180 deg F, then either re-calibrate your brain to compensate, or find an instrument repair shop to re-calibrate the gauge.
The first, and most important step is discovering at what temperature your engine is actually operating. Then you'll know what needs doing.