I have a Jim Coleman Combo Vac/Hot Foam Carpet Shampooer and it takes spells where it won't feed soap. The solenoid seems to stick and I have to turn the needle valve way up to unstick it for the soap solution. I know its not dirt because I have installed a fuel filter before the needle valve to catch any dirt. It has a new kip solenoid valve (acts same as old one) and the solenoid is getting a full 24 VAC to turn it on. The soap solution is feed from the pump, through a needle valve & check valve to a solenoid valve. Any ideas? The check valve has also been replaced.