Mercury 75 upgrade?

[NickT]

I have been pondering having a go at uprating my 75merc 4 stroke to 90 HP for a while.

I have the user manual and the differences between the two original engines appears to be:-

Removal of the restrictors on the air inlet (more air for more HP)
Larger main jet (More fuel for more HP)
1 other jet for idle or similar

I may also need to change the timing a bit

I know buying a bigger engine will be the easier option but I have been looking for ages and all the 115 merc/mariners are around 4k plus another 500 for the swap over.

Does anyone have a view on this please?

I have been spoilt as I have just spent 2 days at all the Sunseeker factories drooling.......

[mark101]

I don't think the extra 15hp will calm your Sunseeker cravings Nick

Remember your 75hp is also worth a couple of grand. So the cost of converting yours to 90hp, plus its value and you're probably not so far off your £4k price. Unless of course you meant it is £4k more than yours?


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[_Ed_]

It would probably be easier just to get some 90hp carbs, what you will find is that the engine will rev higher, but mostly will have the same level of torque/pull/holeshot. The timing will definitely make a difference (even stock) if the 90hp runs more advance.

[NickT]

Thanks for the tips chaps.

The engine for the 75 is exactly the same for the 90 and 115hp versions - just some tweaks made by Mercury to de-tune them to create a range of engines.

I think I will price up the components to see if it is worth taking a punt on this - if the parts come to more than say £300 then it's probably dead in the water.....

Thread drift alert!!!!

Some pics from my visit yesterday - this is a small one.

[Ianfs]

Oi, stop teasing me with Sunseeker pictures!

If I'm reading this right, it would cost about £4k for a 115 engine, but your engine is the same unit with different parts which have detuned it.

Would the best option not be for you to obtain the items which bring it to 115hp, whatever they may be? Or is that too simplistic and a little obvious?

[NickT]

Hi Ian,

It is supposedly that easy...

The 115 has a different gear ratio but that could be sorted with a new prop I suspect.

The engine is actually a yamaha as mercury didn't have a decent 4 stroke back in 2000.

The starter motor has a yamaha label affixed to it!


As it is a carb engine with 4 carbs it would be expensive to swap if I could find them of course.

The block is 1600 cc so I would expect much the same torque if I covert. In fact thinking about it, I probably have lots of torque due to the fact the engine is a detuned big one.

Mark is correct that the cost to change will be minus the value of the existing engine at say 2k.

I may sort out the part numbers in the next week and see what the costs are.