115 Mercury Optimax Losing Power - help!

33JS · 29 July 2018, 20:05

Hi guys, another engine problem thread! Any help much appreciated...

Normally my 6.5m RIB will sit around 32 knots @ 5,000 rpm. Recently she won't make over 22 knots with the revs failing to head North of 4,500 rpm!

So far I've:

Engine was serviced 2 months ago.
I've checked fuel priming pressure.
Battery voltage running is a healthy 14v.
Got a set of spark testers from Halfords and they're all showing healthy at idle.
Checked spark plugs, but they look a bit 'black'. Is this normal for a 2-stroke? Pics at end...
Carried out a compression test on all 3 cylinders and they're all within a hairs breadth of 120psi
The Smartcraft gauge has a non-specific 'Check Engine' alarm coming up at higher revs.

What else can I do before I call out a specialist? I'm kinda flumoxed...

Oh, I did find this fitting sitting inside the engine cowling. Does anyone recognise what it's from?

Plugs:

whiskylee · 29 July 2018, 20:21

You need to hook up the engine to Digital Diagnostic Terminal to find the fault that is showing on your engine

charliee · 29 July 2018, 20:22

The black thing in the top photo is from the engine flush hose.

33JS · 29 July 2018, 20:25

Quote:

Originally Posted by charliee

The black thing in the top photo is from the engine flush hose.

Cheers!

33JS · 29 July 2018, 20:26

Quote:

Originally Posted by whiskylee

You need to hook up the engine to Digital Diagnostic Terminal to find the fault that is showing on your engine

Thanks, was hoping to avoid a call out... damn.

beerbelly · 29 July 2018, 21:07

plugs look like its running very rich

Fred. · 30 July 2018, 06:55

Quote:

Originally Posted by 33JS

with the revs failing to head North of 4,500 rpm!

Quote:

Originally Posted by beerbelly

plugs look like its running very rich

On my screen the middle plugs looks alot richer than the others, like its not running as well.....! ( plug looks old as well judging by corrosion)
Considering the engine is not running right, & picking up the revs when the carbs are wide open, the plugs would look richer wouldnt they ?

Sorry, you may of done this, but i would start by fitting new plugs & try it - Eliminate 1 item at a time !

After that, i would swap the middle coil for one of the other coils if possible ? & see if the plug colour changes on that piston

whiskylee · 30 July 2018, 08:52

The Optimax needs hooking up to a DDT to establish what is going on, don’t throw money at parts until you have read the fault codes. I cooked a 150hp Optimax a few years ago by not having my smartcraft gauges connected ! Just book into your local mercury workshop and have them read the fault, there is a lot going on with a Optimax engine, compressor, air injectors, fuel injectors etc etc