2002 Mariner 115 EFI juddering and low on power

[AdamK96]

Hi,
This is my first post on here, so here goes!
We've got a Mariner 115 EFI fitted to our Gemini Waverider 550, and recently it's been causing both us and our mechanic headaches. It went in for a service because it had been stalling and seriously restricted on power towards the end of last season, and after extensive tests and two injector cleans we deducted it was down to poor quality fuel in the tank.
We filled up at BP and put the boat in the water, and the issue is worse than ever. It is now juddering a lot, causing the whole boat to shake around, and still stalls almost every time we put it in gear.
Have any of you had similar experiences or any idea what could be wrong now?!
I am going to try with a small external fuel tank tomorrow to bypass the fuel system built into the boat, but I'm not too hopeful!

Cheers

Adam

[warder54]

Sounds a lot like my old Mariner 60Efi. Ran fine from cold but behaved like yours if idled or restarted when warm. Turned out to be a temp sensor fault I believe (traded in after a spoilt break to Etive last April) bit the bullet and bought a new Yam 60.

[matata]

Check the compression first... once thats ok then move on to rest of other things. Do you think its dropping a cylinder when at idle or running rough with more open throttle.? Have you tried pulling of a HT lead in turn to see if you can track it down to a particular cylinder coil fuel injector/carb? Nik

[uncle al]

remove the spark plugs and look at the electrodes, are they all the same colour? if one or two are a different colour try them in another cylinder.
Have you tried squeezing the primer bulb, any shit in the fuel filter/s?

[AdamK96]

Cheers for your replies!
I'm going to try the new fuel tank tomorrow and see if it makes a difference and clean the filters again. Fingers crossed! 🤞
If that doesn't work I'll take it off the water and start playing with the HT leads to see if anything improves