mercury 4hp 4 stroke??

markwade · 03 October 2009, 11:24

Hi all, this is my first post as I am new ti SIBing, my 2M Honwave lacks a bit of go with two people in it whilst using my 2hp Honda motor, I was thinking of saving for a new 4hp Mercury/Mariner/Tohatsu. I see in the Mercury brochure that the 5/6hp motors have the same weight and same displacement engine, does anyone have much experience with these outboards (maybe the 4hp will be enough, but can you ever have enough?) and does anyone know what it would involve to up the power of the 4hp to 5 or 6 hp if the engines
are indeed the same. Cheers in advance. Mark.

Nos4r2 · 03 October 2009, 11:36

Welcome to Ribnet

If you want it to really shift, get the biggest rated HP engine it's rated for-in 2 stroke. A 6hp 2 stroke will cost you less 2nd hand than a new 4hp 4 stroke too.

Downhilldai · 03 October 2009, 14:23

....and it won't weigh any more.

Turbodiesel · 04 October 2009, 08:32

But dont forget if your wanting to buy a new engine you cant buy a 2 stroke unless your a commercial user

markwade · 06 October 2009, 00:24

thanks for the replys, at the mo I'm really not sure what to do, I'll get me thinking cap on during winter and hopefully come up with a P of A. Think the Honda 2hp will possibly fetch maybe £180 on ebay so that could be ploughed into the cost of a 2nd hand 2stroke motor.

chewy · 06 October 2009, 00:31

Whats the max hp it'll take?

markwade · 06 October 2009, 12:07

the data plate states a 4hp so thats what I'm going for but going back to the original post it does seem that the Merc/Mariner/Tohatsu 4/5/6hp motors could possibly share the same engine and was wondering how easy it it to release a bit more hp from the 4hp.

Locozodiac · 06 October 2009, 13:59

Merc/Mar/Tohatsu 4 strokes 4,5 & 6 are same block, that is 123 CC, carb restricted, a matter of changing jets for the upper model.

Happy Sibbing

markwade · 06 October 2009, 16:49

thanks for that Loco I was suspecting something along those lines, I like the idea of running a two stroke but following testing my 2hp 4 stroke honda in a water butt there was nothing to see on the surface of the water, next came my father in laws old evinrude 4hp 2stroke twin, there was quite a bit of oily scum on the surface when we had finished!! in the evinrudes defence I think it was a bit oiled up and would have cleared up with a bit of a run but the difference was still suprising. Still love the sound of the evinrude though.

Downhilldai · 06 October 2009, 18:05

I didn't realise you were planning to use it in your bath.

samt · 06 October 2009, 20:07

I've run a 6hp carb on a 4hp with success.

markwade · 06 October 2009, 22:14

Hi all,
Thanks for all the replies, as with any new hobby there is always plenty of new info to absorb and plenty of potentially expensive mistakes to be made.
Samt, does the 4 to 6 hp mod require just fitting the carb from the 6hp engine, are there any other mods which need to be carried out at the same time ie throttle linkage, fuel supply etc? Cheers, Mark.

samt · 07 October 2009, 11:48

Quote:

Originally Posted by markwade

Hi all,
Samt, does the 4 to 6 hp mod require just fitting the carb from the 6hp engine, are there any other mods which need to be carried out at the same time ie throttle linkage, fuel supply etc? Cheers, Mark.

It was just a straight swap. Unless you can find a secondhand carb, expect it to be an expensive part new.

Downhilldai · 07 October 2009, 13:45

Is the body of the carb different, or only the jet(s)?

9D280 · 07 October 2009, 14:14

Sounds like an easy uprate.....

At risk of bringing up the monthly discussion about power over & above the rated number - I have but one word ..... Insurance?

samt · 07 October 2009, 15:25

Quote:

Originally Posted by Downhilldai

Is the body of the carb different, or only the jet(s)?

The body of the carb is slightly different. But it fits straight on.

We use these engines in a hire fleet at work. They get alot of abuse and they are the toughest 4hp avaliable. I have alot of spares and old engines to play with. I think a new carb would cost over 200quid. So you may aswell just buy a new 6.

PAULJ1993 · 16 January 2017, 02:14

Sorry to reopen this thread after a long time I was just wondering would the mercury 6hp main and pilot jets and the main nozzle fit with the mercury 4hp carb or would i need to replace the whole carb thankyou

samt · 16 January 2017, 06:24

The throat of the carb on the 6hp is about twice the size of the 4hp. You'd have to replace the whole carb.