Sunil this worked. For anyone else the Number conversion was critical. The code above is:
dataPoints.push({ x: i, y: Number(parsed_json.history.observations[i].tempi}));
But the parans are wrong (typo there). So fixing the typo you get:
dataPoints.push({ x: i, y: Number(parsed_json.history.observations[i].tempi)});
This works fine!
Thanks,
Jim