My son and my grand-daughter are working on her great-grandpa's 1942(?) H. They've put in new sleeves, pistons, rings, manifold, and other necessities. It runs real sweet for about ten minutes. The sediment bowl fills up with a stringy molasses-like substance and impedes the flow. Clean it out and you're good for ten more minutes. It sat with old fuel in it for years, and the stuff turned to something I've never seen before. When they brought it home, it was dry and hard - son put clean gravel inside the tank and strapped it to a jacked up tractor wheel and let it shuffle for hours. It got some of it loose, but there's plenty more. Now it seems like the gasoline is softening it up and letting it cause havoc. He says there's a baffle in the tank, and that doesn't help. Surprisingly, the tank doesn't seem to be rusty inside. Just the molasses. I wonder if carb cleaner and another good spin on the tractor wheel would loosen it up. Anyone have any recommendations on fighting this gunky stuff?