When motor is at idle speed it surges

Air in system hold wand trigger clsed until it runs smoothly.

Trigger for wand needs replacing, water bypassing it and not allowing pressure build up enough to close pressure switch, allowing engine to go back in idle

Your carburetor and its jets need a thorough cleaning to restore proper operation. The idle circuit is the culprit in your case.

Common problem across brands. When you spray water the drop in pressure triggers the motor to take the hose pressure ~ 30 psi and boost it to ~ 3000 psi. Water coats these parts with calcium (hard water) or other junk and water contains bacteria which causes slime and scale. Once that pressure switch / valve is sufficiently clogged it doesn't move smoothly so it can fluctuate between sending a yes / no signal about whether you are squeezing the trigger or not. This causes the pulsing.

EZ test: take the the tip off the wand, start the unit, squeeze trigger - should run continously with no problem. If it does for sure you need to watch a video on dissembling and cleaning the valve body. It is not hard but you must work carefully to avoid losing parts especially springs and take digital pictures to record the order for reassembly.

sounds like air fuel mixture screws are out of adjustment..start with the on marked (L)..this is the low speed(idle) adjustment...turn it in all the way just until it stops..but be gentle..then you wnat to turn it out 1 1/2 turns as a starting point..start the engine and adjust it until you get a smooth idle...next, with the saw running, pull the trigger and you should have a smooth response from slow to fast...you can adjust the (H) screw until you get good high speed operation...if these adjustments don't fix the problem thenm yoou may need to have the carb rebuilt( a carb kit is usually only 15-30 dollars)

the surging and whistling sounds like there might be a vacuum leak that is causing this.recheck all vacuum lines and surfaces were this is a gasket that seals a vacuum source.smooth running and good power off idle suggest this leak only affects the motor at a low(idle)rpm.

sounds like its breaking down, check your ignition system, test your leads, check your plugs, check your ignition coils etc etc etc.

Usually that is a sign of the carb not being adjusted right. Run it at full throttle and adjust the main mixture needle (usually on the bottom) until it runs the smoothest. Set it in the middle of the range where it runs smooth. Then set it down to idle and adjust the idle mixture until it runs smooth at idle. Accelerate it rapidly and if it bogs or hesitates turn the idle mixture a little leaner (clockwise) and try again until it works right. That should get you very close. Try tweaking it a bit from there. as the microscopic specks clean out of it, it may need more adjusting.

this prob happens allways in carburated engines that the car or motorcycle is running lean or rich . because the air - fuel mixture ratio is not right . so you should open the carburator and remove the air filter you will find two screws in the lower front section of your caeburator. you can adjust them by a screw driver until your car is smooth

the 2001 altima is what i have and I had the same problem as you. turned out to be a bad head gasket factory used cheap ones for a few years before they found the problem. one way to test this is to get a can of carborator cleaner and spray it around the area where the head meets the block under the intake problem should be around the 4th cylinder or close to driver side. if the head gasket is bad the rough idle will smooth out while you are spraying the head.