Evinrude misfiring low RPM

[Dhf]

last night I prepped the boat for a 40 mile round trip to Ramsey and the surounding islands, The outboard started first time with only a blip of smoke from being winterised in January, We departed the river Cleddau with no probs on low rpm for 10 minutes then we picked up to 3200 rpm with no problem for 10 mile, Then half way through Jack sound I noticed my c-map gps went off, so I pulled back and quickly checked the battery to discover i'd left the 2st oil tank cap off from filling the night before, It was messy but i'd only lost a pint or so, Not to worry so I carried on to discover the engine started misfiring under 2000 rpm, And I needed low rpm speed to pass some overfalls, Plus I noticed there was 3 inches of travel on the lever before she'd increase splutery rpm upto 2000 rpm, I could see Ramsey only another 8 mile North and it was very tempting to carry on but I knew i'd need low speed on some stretches, So we traveled up the south of skomer and returned to Port at 3000 rpm with no hickups, Opened her up to full throttle in the haven with no problem she sounded great,
Only thing new on her since last season is a new fuel filter and housing fitted just before the flow meter which was also playing up at all rpm, but was working fine reading 26mpg at 25knots, I did notice the new fiter housing was fitted a few inches higher than the old one.
Any advice why she would give trouble at low rpm would be much appreciated.
Thank you

[Pikey Dave]

Check the new filter & housing for air leaks. When you say the fuel flow meter was playing up, what do you mean? Maybe it was working fine, but responding to air/blockage in the fuel line. Was the fuel primer bulb still full or did it collapse? If you get problems after making changes to any system, the first place to look is where the changes were made, in your case the filter. After that it could be anything, plugs, coils. You could do with getting the engine onto a laptop with the diagnostic software & doing some tests if the obvious stuff doesn't work. Good luck!!

[Tim M]

I had a similar issue on my Evinrude 135 DI - turned out to be the plugs (not cheap!) - changed those and it ran sweet as a nut after.

[MarkM]

Plugs only last 100 hours, they get extremely hot.
I regap and clean them after 60 to 70 hours and change them at 100 to 120 hours.
Do you have the right, expensive, plugs?

[Dhf]

The flow meter was giving me average readings of 2.3 to 3.5 litre per hour when it started playing up and it was reading the same upto 3000rpm, Which I know should have read about 25 lph at 3000 rpm, I thought if it was blocked or air lock then the engine would play up at all rpm but it was fine above 2000, I'm guessing it must be something to do with the new filter setup as mentioned, I'm thinking maybe the lift pump at low rpm not coping with new setup. I did notice the oil line bulb had lost a bit of pressure after leaving the cap off but 1 squeeze and it was solid. The plugs have had about 50 hours use and there from cooper marine, Champion XC12PEPB. Maybe I should look to replace them soon. Primarily I think i'll call the engineer out as he was the one who fitted the filter housing and flow meter.
Thanks for the input guys.
A problem aired is a problem shared as they say.

RE: In the first post toward the end I ment 26 LPH at 25knots.

[Pikey Dave]

The low pressure lift pump is powered by pulses of exhaust gas from the crank case, if the pump diaphragm is holed or there is a restriction/air in the fuel line, the pump might not be able to deliver sufficient fuel until it gets some "oomph" at higher revs. The LAST thing you want is a DI engine running lean/fuel starved or you risk melting a piston.

[Dhf]

Cheers Dave I'll certainly get that pump diaphragm checked out, Is it an easy job to check it, I would'nt have a clue what it looks like, Trouble is I aint no mechanic and only know very basic engine maintanance, I know how to line the plugs up and thats about it. I'll check the tinternet see if I can find some diagrams.

[willk]

Originally Posted by Dragonhawk ficht

Is it an easy job to check it

In my experience, very easy to open!

Somewhat trickier to refit...

[Dhf]

Cheers Willk I will proceed with caution, An call the engineer me thinks.