dear AnnMarie,thankyou for your reply.By up at 45 degrees I mean its half way between fully upright and a true sidewinder.Th e cylinder is well clear of the cowling and sits in the full face of the airflow.How about this? If you run a motorcycle engine on fully synthetic oil before it is run in you can destroy the motor by virtue of the fact that the piston rings are not allowed into enough contact with the cylinder.I run 100% synthetic,could this have had a detrimental effect on this OS 91fx???