Just moved into an old Victorian House (Second Floor of Three). The kitchen faucet is the single handle type and the pressure is horrible when it is turned to hot and it takes forever to heat up. The pressure is so low that soap doesn't even bubble up when the hot is on. Pressure/temp is fine every place else in the house. Also no shut off valves under the sink. Plastic tubing leading to metal pipes in the plaster wall.

You will have to find a way to shut the water off to the entire house or possibly there is a cufoff somewhere in the line in the basement if you have one.

Turn the water off and take the faucet apart and take the cartridge out of the faucet and inspect it to make sure there is not buildup in the cartridge, Also look into the holes in the faucet to make sure the one on the left is not stopped up.

Put it back together and turn the water on and see if you have solved the problem.

If not you may have to find a way to get into the wall and disconnect the plastic from the iron pipe to clear that area out.

Letmeteelu is right however on these old houses the cast iron pipes are the problem they retain rust and other debris that will clog all new low volume fixtures. All of today's pipes should be copper. Anything that runs horizontial will corode and giveclogs in the future!