The OS 32 shouldn't be a problem, they are usually pretty stable. The Raptor is a different story. The standard fuel lines are suspect and should be changed for good quality fuel line. One other point in the fuel line is the connectot that sits in the mouth of the tank. The clunk line fastens to it on the inside and the line to the carb fastens on to it on the outside. This little tube need checking for plastic fash or depbris...it happened on mine and took me nearly 6 months to find.

Best thing is to start from srcatch. Remove all fuel lines, filters and carb. Strip the carburetter down to nothing and clean it well, rebuild it and set the intial settings to those in the manufacturers leaflet. Replace all the fuel pipes including the pressure line to the muffler and go from there.
The 15% fuel shouldn't be a problem unless it's not been stored properly, but a new half gaallon wouldn't break the bank and would prove a point.

A really good source of information on the Raptor , especially engine set-up is [link=http://www.raptortechnique.com/index.html]Raptor Technique.[/link]