Suzuki Club UK

my head was the same.
if you want to just clean the head i would use a can of break cleaner or carb cleaner. it blasts the dirt about and helps thin it so it all runs out.

Wow that's filthy, took mine off to do the tappets the other day and was amazed to see how clean it was! Not bad hey? Just a shame it died tonight, its parked up in a lay by down the round feeling sorry for itself! I hope it's still there in the morning

Personally I think that you should remove the head and the sump (which will be just as bad) and get it chemically cleaned by a professional engine building company. The oil filter and oil galleries will have no chance to deliver the flow of oil at the correct rate with it all gummed up. I'd be very surprised if an off the shelf cleaner will do an adequate job.