the owner changed injectors then I got the engine to find out what was wrong, I cleaned the vst and replaced the filters (the main racor to engine,the small one on engine and the one between pump and vst, the injectors could be clogged but I dont think so because the engine will run smooth and throttle up to high rpm when I disconnect the vacum hose to the fuel regulator but I don"t know why it responds that way, I ran the engine at idle for a couple of minutes and touched the ISC valve and it was hot, I see that there is a small filter going to the ISC and I wounder if it is clogged...with the vacum line attached to the fuel regulator if I just start to throttle up the engine dies right away but if I disconnect the vacum hose from the fuel regulator and throttle up it reacts just fine...whats the deal? could it be a bad ISC or clogged filter to the ISC or both? While we are talking diagnostics where can I buy a yamaha yds diagnostic 1.33 software and harness kit? thanks for the help....I checked the fuel pressure when the motor bogs down and the pressure stays at around 40psi