hey i bought a wr 250 that had been stood for four years or so ,i worked at the nrma workshop in town at the time and we had a product the we had to put through subarus on a service its called upper engine cleaner we used subaru gen we bought by the box not that expensive ,it was injected in the inlet manifold via a vacum pipe ,it smelled ver much like amonia, they said it was to clean the varnish off valve stems to stop sticking valves ,the fuel in the caby on the wr had dried up and wouldnt budge with carby or brake clean ,but this stuff was the shit it dissolved it in no time ,you can get it from repco engine conditioner its called ive not used that one but is supposed to be for the same application its on offer for a box too at the moment hope this helps