counterbalancer is bad
Under the air filter box, above the engine crankcase, behind the belt/clutch housing.
Knocking is usually associated with worn main and rod bearings.
The drain plug for the crankcase on a 1997 Polaris Scrambler 400 is typically located on the bottom of the engine case. You may need to remove the skid plate for better access. Look for a hex or bolt-type plug, which is often positioned towards the rear of the engine. Always ensure to have a drain pan ready to catch the oil when you remove the plug.
it could be your valves or your engine
Mine did the same, mine was a motor mount.
Knocking as opposed to pinging or ticking, usually means seriously worn bearings of some sort. Time for an overhaul.
2 cycle engine oil. I prefer to use a synthetic designed for ATV's and Snowmobiles. It doesn't smoke as much and stinks much less.
You can find the serial number for a Polaris 500 Scrambler typically on the frame of the vehicle. Look for a metal tag or a stamped number on the left side of the frame near the front, close to the engine area. Additionally, the serial number may also be found on the owner's manual or on the vehicle's registration documents. Always consult your specific model's manual for precise locations.
knocking noise
For a 1997 Polaris Scrambler 400 4x4, the recommended gas-to-oil mix ratio is typically 40:1. This means you should mix 3.2 ounces of 2-stroke oil per gallon of gasoline. Always use high-quality 2-stroke oil and ensure thorough mixing to keep the engine running smoothly.
The combination of fuel still being pumped into the engine and air
It depends on a trailblazer 250 they have no crankcase oil but on a 400 water cooled scrambler they do so yes you need to change the oil with regular motor oil