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Old 29 July 2018, 15:05   #1
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Country: UK - Scotland
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115 Mercury Optimax Losing Power - help!

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:




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Old 29 July 2018, 15:21   #2
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You need to hook up the engine to Digital Diagnostic Terminal to find the fault that is showing on your engine
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Old 29 July 2018, 15:22   #3
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RIBase
The black thing in the top photo is from the engine flush hose.
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Old 29 July 2018, 15:25   #4
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Quote:
Originally Posted by charliee View Post
The black thing in the top photo is from the engine flush hose.
Cheers!
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Old 29 July 2018, 15:26   #5
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Quote:
Originally Posted by whiskylee View Post
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.
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Old 29 July 2018, 16:07   #6
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plugs look like its running very rich
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Old 30 July 2018, 01:55   #7
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Quote:
Originally Posted by 33JS View Post
with the revs failing to head North of 4,500 rpm!

Quote:
Originally Posted by beerbelly View Post
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
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Old 30 July 2018, 03:52   #8
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The Optimax needs hooking up to a DDT to establish what is going on, donít 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
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