Hi. Ive had a poke about this morning and it wont even start now. Plugs are black and wet. When it started yesterday it was chucking black smoke out the exhaust. Ive checked oil cap and dipstick and there all sound. The oil i took out stunk of petrol and was very sticky. Like a glue type consistency? Could the previous owner have added an additive to mask a problem? Just weird how friday it ran like a good un and saturday it wont??