Working quickly, beat hot syrup into the gelatin mixture at slow speed then incorporate the pumpkin mixture and the tartar (if using).
In a large saucepan set up the thermometer. Combine the corn syrup, sugar, and the remaining water and bring the mixture to a boil. Continue cooking over medium heat until the thermometer reaches the "soft candy stage" or 238-240 degrees F. Immediately remove from heat.
In half of the water add the gelatin and stir with a fork until fully dissolved and there are no lumps. Separately, mix the pumpkin puree with the vanilla and spices.