2006 115 yamaha 4 stroke

i purchused a 06 yamaha 115 4 stroke from a dealer new old stock for a deal. i have it on a 24 ft pontoon and have about 33 hrs on it. it was serviced at 20 hrs and was running fine after i had to bring it back because of a cut o ring on one of the injectors. they cut it when they took the fuel rail off to clean it. now im having a prob with it at low rpm. it started when i was back trolling because of no wind and after about 30 min i went to take off and it ws like a 2 strke that was loaded up. it sputtered and had to run for a bit to get it straightened out. (so i thought) it showed itself again 2 weeks after and has been doing it off and on since. it will plain out and run good and turn up to 5600rpms like it did when i got it but then drops slowly to about 5200. i found a small split in fuel line coming from tank to water seperator and cut and repaired it but problem still there. ive drained seperator, filter bowl on motor, and high pressure fuel canister behind the manifold. no water, no trash. any ideas? i have a warranty but they said if its anything not under warranty i will be billed so just trying to cover myself. any help on this will be appreciated.

GARY

The "dropping from 5600 to 5200" sounds like it could be the fuel pressure dropping, but on my f115s when the VST filter was plugged the motors would run fine at idle or low rpms. If the motor is running rough at low rpms and then is able to get up to 5600rpms it's possible an injector can be acting up. To test the injectors electrically you use an ohm meter and check resistance. Pull the plugs on the injectors and test each injector. But first test your ohm meter by touching the two leads together.........it should read about .75-1.0. The resistance should read about 15 (mine were 15.4-15.7) but most importantly they should all read close to the same (+- 0.5).

A fuel pressure gauge would tell you if you have a leaking injector as I believe the fuel rail is suppose to hold pressure for a few minutes.

If your problem is electrical I can't help and you'll probably have to have a tech with a monitor.

Good luck