Gas Pressure Washer: Pressure washer won't mix detergent with spray
Using the wrong spray tip to apply detergent can prevent the detergent from mixing properly with the spray. Use the low-pressure spray tip (usually the black tip) when applying detergent. A clog in the detergent siphon tube can also inhibit proper detergent mixing. Check the siphon tube for a clog and clean the tube if necessary. If the siphon tube is clear, then you'll likely need to replace the chemical injection kit on your pressure washer.
These repairs may help solve your gas pressure washer problem
Repair the pressure washer chemical injection system
The chemical injection system siphons detergent from the soap container and mixes the detergent with the spray. If the detergent doesn't flow through the system, check the chemical injection components for clogs or defective parts. Replace any defective chemical injection components.
If your pressuring washer isn't spraying soap, the chemical injection valve might be the problem. This repair guide shows how to replace it with a pressure washer chemical injection kit, in 5 easy steps.