[Citizen]

Hi Everyone,
This is my first time on this site and I probably don't have any of the info I am sure that you are going to ask me for.
Last summer I bought a Mariner 40 oil injection outboard engine. It starts well, idles well, runs well at low revs, but when I increase the revs to go a bit faster it judders and seems to slow down. I can't seem to get more than half power out of it.
Sorry if this all sounds a bit vague but not only is the engine new to me (its not a new engine!) but boating is also rather new to me as well.
Thanks for all your help

Citizen

[Plainsman]

Welcome to iboats!! I'd check, compression, spark and fuel. Also post the serial #