Laigalih,

I had a similar issue with my P-70 after having it sitting for a long period of time. What is the message you are having on GSU after the failed start? is it "Accel Slow" ?
Would suggest 2 things:
A- disconnect fuel Lines and test valves separately, letting fuel flow out of tubes to dissolve possible restriction. Then leave the tubes disconnected and initiate a start, kero plug line should start dripping fuel while main fuel Line should not, then at second stage/ramp you should see fuel dripping from the main Line. I f this is what you get then suggest you re connect lines and attempt a start.
B- if after doing above test your problem still persists, suggest you check/ clean or eventually change your O ring starter. Re- attempt a start.

Hope this helps.
Regards,