New Mercury 40HP Outboard break-in

[Quobba]

Hi all

Looking for some advice and guidance on new motor break-in

I have a brand new Mercury 40HP Lightning XR. During break-in, I followed the manual's break-in instructions to the letter:

added oil to the fuel in addition to the injection oil;
kept speeds down. half speed for first hour, half to 3/4 for next 2 hours and three qarters up to the first 10rs, etcAfter the first 10 hrs all was well - was getting speeds 40-45km/hr at WOT, which I only applied for short distances.

Then on my last trip, (15 hours) I notices top speeed dropped off considerably, and I strugged to get up to 30km/hr WOT. I had been doing a bit of trolling, so I thought the extra oil may have clogged the plugs.

Took the boat in for a 20hr service last week, then tried it out today with the same problem. Not adding oil to fuel any more and the motor struggled to get up on the plane and up to 30km/hr again!

Could anyone advise a possible reason for this problem and advise (roughly) what speeds I should be able to attain in my 4.5m alum side console? Should the 20hr servicing have picked up this issue?

Any advice would be appreciated.

Quobba :-/

[cormorant]

Unless you mentioned a performance problem when dropping it off they wouldn't have looked for anything. They service them to schedule and assume there is no performance issues.

Did they check or change plugs?

Fuel system is where I'd start. Fresh non ethanol fuel?, filters clean , Bulb and fuel lines no restrictions, carby not full of water, tank fuel vent open? choke operating correctly. Then spark? plugs OK, leads and coils OK?

Others - bent prop? Is it using extra oil? Using right oil? Have you changed trim of boat or motor - up or down a hole?

Phone your dealer and tell him the story and ask his advice. You obviously aren't reaching full revs or do you have a prop airation issue? If it isn't a set up issue he should get the motor back in the workshop and spark , compression test it and put on a test wheel and check max revs etc in the tank.

Tell us how you get on.

[Quobba]

Thanks cormorant

I will be taking this back to the dealer tomorrow, but could you advise what speeds I should be obtaining WOT?

Or is this a 'how long is a piece of string" question?

Quobba

[cormorant]

Can't give a definative answer on what speed but the key is the difference in speed you have experienced.

Add to the list -are you still getting full throttle- cable moved or obstruction.

Silly question - were both speeds measured by GPS - not a water wheel or pitoc tube ?? Just checking your numbers are real?

Others will know comparative speeds as they will have similar boats.

You can work out your theoretical maximum speed by multiplying max revs by gearcase ratio by pitch on prop. Obviously there is slippage of that number as props aren't 100% ffecient and you have wind resistance and friction but that will give you a max possible speed.

[BARRAkid]

I get 50kmh out of my 6 month old 40hp suzi on a 4.2m stacer decked out
so my guess is 45kmh :D