150 4 stroke mercury - Im stymied!!

[RST]

I have a 2013 150 merc 4 stroke. Last year after trying to get it over 4000 RPM it would just die off till I throttled back. Runs fine up to that RPM. I change water/fuel separator and low pressure fuel filter - no help. So - get a tune-up last month (mercury mechanic) and tell mechanic; he calls saying it was only a bad plug ( sure seemed like fuel problem to me). Go out and all fine up to 5000 RPM for 30 minutes - then it sputters and dies back till I throttle back under 4000 RPM again. HELP!!!! Not sure where to go from here
Thanks for any tips!!

 

[Chris1956]

Clearly you need to make sure your fuel system doesn't have a restriction. Check antisiphon valve. See if A-S valve has its own filter. Some do. You can remove it for test.

FTR- I think your mechanic was fibbing.

 

[racerone]

If you have an on board tank , then test run with a portable tank and hose.------

 

[Faztbullet]

Verado?