slow heating radiator

Peter King

Recently moved into a house with appx 10 year old gas boiler one-pipe steam system. One of the two mains is pitched downhill most of the way, but halfway around the basement it turns a 90 degree corner, goes from 2 1/2" down to 1 1/2", and starts to go slightly uphill. After about 15 feet a riser shoots straight up to the second floor and feeds a radiator. This rad takes forever to get hot. Usually only the first couple of fins get hot before the thermostat gets up to temp downstairs. The air vent on this rad spits and hisses like crazy. It is only marginally better when I shut the valve on the one remaing rad on the line, a rad on the first floor whose air vent spits like crazy, too. There is no vent at the end of the main, but looks as though there use to be one that was removed and capped.

So my questions are: 1) does the fact that the main goes uphill cause problems, 2) do I need a vent on the end of the main, if so what size and brand would you suggest, 3) would insulating the mains help, 4) do I need to replace the air vent on the rad, if so, what brand to you suggest? I already replaced it once with a new Maid 0 Mist with a big apeture. Any suggestions out there? Thanks.