Mercury Optimax Question

I bought a new Mako 18LTS about 4 years ago and it has run great. That is until a few weeks ago. The motor runs great anywhere for just above idle to wide open. However, at idle it has begun to spit and sputter and even cut off. As best I recall, I had recently filled up with some straight gas. Even though it is straight gas, it can still have trash in it. So, I'm hoping there's just some trash in the fuel filter. Does anyone know if the fuel filter is likely just an inline filter between the tank and engine, or is it actually on the engine?

Any help is greatly appreciated.

TW

What horsepower and year?
I have 75 hp 2006 and filter in under motor cover a on side of the engine

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My pro xs idles rough when I put 87 in it but she purrs with 89 or higher even though the manual says she’s set up for 87

I have a 2014 115hp and there’s rarely been any sort of hiccup or brief sputter at all. I started running straight gas about 2 years ago - not sure of octane. I do think I had more or less just filled up when I had this issue pop up. Again, it runs great anywhere above idle or neutral.

Here is a diagram showing vapor separator. Shows filter, pumps and how it is assembled. You can change that filter without disassembly. But I would take it apart if you are mechanically inclined and check for water. Also they have had a problem with that float Assy. They have a tendency to stick. They offer a upgraded float kit.

Mercury Mercury & Mariner Outboard Parts by HP & Liter 115HP OEM Parts Diagram for Vapor Separator | Boats.net

Probably the piece of junk float switch in the fuel module. Mine went bad in my 2012 and it would sputter and almost die out at different stages, sometimes idle, sometimes throttled down. The float switch appears to be a $2 cheap part but they'll charge you about $60 online. It completely solved my issue. It will take about 1/2 hour to replace and is a pretty simple fix. Hope that's the issue because it pretty simple fix.