Speaking of foam......I highly recommend Sea Foam.
It is available at Pep Boys or any auto supply. I bought my wife a used bike with very dirty oil & tried this trick: Put a little SF in the cranckcase, ride it about 20 miles to "stir the pot" real good, then drain your oil. I would then put some cheap oil in it for another couple hundred miles & drain again with a new filter. Then you have a totaly clean crankcase & get rid of any crap in the system.
SF is also very good as a fuel additive to clean out the injectors & carbon deposits.
"THERE IS NO SUBSTITUTE FOR VICTORY" General Douglas MacArthur