Download: 2nd Dolmar PS7900 (woods ported stock muffler)
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This is my second crack at porting a 7900. This one was ran over by a logging truck and needed a new fuel tank assembly. I widened the intake and exhaust wide as piston skirt would allow, Also cleaned up the transfers and added some finger ports routed around and above the intake port for better scavenging. Timing was advanced and head gasket removed to the tighten up the throttle response. Also the carb limiter caps were cut off. I did not finish the muffler mod, so I put a new stock muffler on with the screen removed. There is some more left on the table for power, timing could go further, and the cylinder could be decked to improve compression, as it stands 170ish psi of static compression.