Optimax 225 idle surging below 800 rpm

[Venzel]

I have a 2000 optimax 225 that has 385 hrs total. it starts very weel when hot and cold with a litle trotle. It idles perfect hot or cold when its in neautral only.
when in the water and in gear, it is surging below 800 rpm, above 800 rpm, there is no problem at all. Hole shot and WOT is all perfekt to.

I have got the engine upgrade to around 250 hps, done by Lundin Marin SE. Flash of ECM and installing Boysen reeds. Also injectors have been cleaned and inproved by Lundin Marin. All 6 fuel injectors and 6 direct injectors was in wery good condition, after cleaning and testing.

Before upgrading, the engine was complete overhaul with pistons, bearing and all.

The Quicksilver DMD- tester tells no failures, and then i have replaced following components after, just to make sure:

All filters, sparkplugs and diaphragm assy 804533. All hoses for fuel is replaced, and fuel rails is cleaned.

My last Shot in the gutter, is compressor reed plate assy 835088A10, and compressor filter.

I am to be a litle frustratet, so I hope that somebody can give me some good advise here

[rchavis]

I see you said all filters .....do your engine has a filter inside the Vapor Separator Tank (VST )....are the needle valve could be going bad or a fuel pump ....just throw some things out there . The Pro's will be on later ?

[rchavis]

I would also move this over to the Mercury forum ....you will get more hits 3 L (forum )

[kry29]

I had one that did the exact thing and i got it better but never completely solved. One thing you can check is the throttle plate air gap. You will have to ask don weed how to do it because I forgot.

[underestimated]

O ring on injector can get a little dry rotted. It will give this exact symptom. Only surges at an idle.