I tried to start the pressure washer by lulling the cord, there was sharp popping noise, and the engine would not crank to start. It is a Honda K. washer. What went wrong? Pls advise, thanks.

You need two things for the engine to start, spark and fuel. Pull the plug, hold it close to the engine and pull the starter cord- check for spark. If there is spark (most likely there wil be spark), then it is a fuel problem. Try a little startiing fluid into the breather and see if that gets it to start. If that works, then the problem is in the carbureator - it probably needs to be rebuilt if the engine has been sitting for a while.

First, turn off the water, disconnect the water hose,,,.if it will start, ...then work on the water pressure valve....

This is typically due to the unloader bypass valve not operating properly. You can remove and clean this valve or you may want to replace the valve with a new one.
If you take the high pressure hose off of the pump and with the water turned on you can start the engine each time then you probably should replace the unloader bypass valve.

Here is a link to the pump.

http://www.allpartsinc.com/mmAllParts/Others/A14292-001.pdf

This is a problem with GC-160 and GC-190 engines on pressure washers, tillers, etc. Once they get some hours on them and as things seat in-wear in, they get to a point you can not pull the start cord. If you remove the spark plug, the engine turns easily then the valves need adjusted. The valves are set .005" to .006" off the seat. This allows enough compression release but the engine runs. I find the valves need adjusted every 25 hours, not the 100 hours Honda states.

gas only lasts for 30 days in small engines try fresh fuel but you might need to clean the carb out

if the fuel tap has been left on it may have fuel on top of the cylinder and would not able to pull cord.
if so take the spark plug out and turn over,fuel may come out of hole.replace spark plug and try to start. if it still won't turn over,you will need to take the face plate off the motor. remove and inspect if there is any foreign objects. try to turn motor over by hand., grab on to fly wheel & turn. if it moves freely it may be the pull start it-self. try pulling the cord out. if no problem assemble and try to start.

you need to keep the gun open so allowed water to flow and not overpressure the pump.

Try removing the spark plug then pulling the cord! If the cord pulls then you cycle the engine a couple of time to see if fuel is coming out of the spark plug hole! If no fuel present replace spark plug and try starting the engine. always have water running through your washer before you attemp to start!

Before you trash the pump, try this. Get a very good flush through the entire system from faucet to trigger. Let it run for say, 5 minutes. Make sure that there are no high spots in the hose supply line where air can be trapped. Once done, start the engine, but this time with the trigger depressed on the spray nozzle. This acts like an unloader, and makes it much easier to start, as there is no back pressure. I had a P/W that I had to crank that way. It worked for me. I have a new one now, and I still crank it the very same way. One last tip: If you need to shut down the machine, say, for a pit stop or lunch, leave the trigger depressed with the engine off. It allows the pump to cool, and makes re-starting much easier.
Best regards, and please rate this solution. Thanx, --W/D--

Most Honda engines have an oil pressure switch that prevents engine damage due to low/no oil pressure. Make sure there is sufficient oil in the engine and that the wire is connected to the pressure switch.