GTS running problem

[roobob]

Hi guys. I'll try to keep this as brief as possible while describing in detail my issue. I'm working on a friend's '98 GTS that has sat for 7 yrs (i know, yikes!). I drained the brown gas, flushed the lines, installed new battery, etc. The craft now starts and runs for a few seconds, then quickly dies. When an immediate restart attempt is made, starter engages but nothing happens, almost like engine is seized, but it isn't. I pulled the head off to verify this. Cylinders are not scored and showing good crosshatch. I have a fairly extensive 2-stroke background, but not in the larger engines and definitely not in a PWC application. It's as if this engine is building up enormous pressure somewhere. After sitting for a few minutes, restart attempt begins with a very slow crank, followed by a backfire, then very fast cranking resumes and engine does restart only to run for a few more seconds. Where is this apparant backpressure coming from? Any help would be appreciated.

 

[sunbaby69]

make sure exhaust is not plugged. what is compression