4 Hp 4 Stroke Tohatsu Convert To 5 Hp

[MickG]

I have 4HP 4 Stroke Tohatsu and I have n oticed in the specs that there some higher hp rating for engines that have the same displacement ie 5HP. What, if anything, can one do to change the power output? Thank you, Mick

 

[JB]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

T-guru may have a simpler answer, but the easiest way I can see is to trade the 4 in on a 5.

 

[TOHATSU GURU]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

Buy a 5 hp or 6 hp carb and replace the 4 hp carb. That's all there is to it.

 

[MickG]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

I take it that not timing or exhaust changes ae needed. Thank you. MickG

 

[TOHATSU GURU]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

No...Its still just the carburetor.

 

[MickG]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

Thank you. Mick g

 

[vtx531]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

Buy a 5 hp or 6 hp carb and replace the 4 hp carb. That's all there is to it.

I tried the jets in my 4hp carb back before we knew the air was fixed. I would like to get the 6hp carb if this will actually work. Do you know of anyone who has tried this. Do you have any part #'s? I have also read that a new carb plate is need in addition to the 6hp carb. Do you know anything about the carb plate?

 

[TOHATSU GURU]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

http://www.internetoutboards.com/partdetail.asp?id=354

Of course it works or I wouldn't say that does. Everyone has been doing this for the last 7 seven years and there is no carb plate to change out.

 

[nondem]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

http://www.internetoutboards.com/partdetail.asp?id=354

Of course it works or I wouldn't say that does. Everyone has been doing this for the last 7 seven years and there is no carb plate to change out.

This is just the information I've been looking for. I've got a friend wanting to do this to his 2007 4HP. We were looking at parts the other day and I'd like to be able to answer the question I know he will ask when I tell him he needs the carb to do the upgrade to 6. Looks like the same carb is on the 4 and 5 except jets - why won't swapping the jets out bring him 5hp with his OEM 4HP carb? Will the carb you were nice enough to post the link for work on his 2007 engine(MFS4BD)?

 

[vtx531]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

Looks like the same carb is on the 4 and 5 except jets - why won't swapping the jets out bring him 5hp with his OEM 4HP carb? Will the carb you were nice enough to post the link for work on his 2007 engine(MFS4BD)?

The carbs appear to be different part numbers.
I think the answer to your questions is no...

3AU032000M CARBURETOR, MFS /NSF6B <-----6hp
3AS032000M CARBURETOR ASSY, MFS/NSF5B <-----5hp
3AT032000M CARBURETOR ASSY, MFS/NSF4B <-----4hp

This should help!
http://www.nissan-outboard-parts.co...Catalog MFS4B-5B-6B (2005) - (00221046-4).pdf

 

[nondem]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

The carbs appear to be different part numbers.
I think the answer to your questions is no...

3AU032000M CARBURETOR, MFS /NSF6B <-----6hp
3AS032000M CARBURETOR ASSY, MFS/NSF5B <-----5hp
3AT032000M CARBURETOR ASSY, MFS/NSF4B <-----4hp

This should help!
http://www.nissan-outboard-parts.co...Catalog MFS4B-5B-6B (2005) - (00221046-4).pdf

Ah - Sorry about my mistake - I looked at the overhaul kits and they were same part number so....

 

[TOHATSU GURU]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

The air jets are not replaceable in each of the bodies so you have to go with the correct carb for each hp. Yes, the link I posted is the correct one for all 6hp models, however, there are two different part numbers for that carburetor that will work.

 

[nondem]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

The air jets are not replaceable in each of the bodies so you have to go with the correct carb for each hp. Yes, the link I posted is the correct one for all 6hp models, however, there are two different part numbers for that carburetor that will work.

Great! - my friend gave the go-ahead and funded the purchase of a new carb for his 2007 "4HP" engine(MFS4BD). Which part number do you recommend? I'll go ahead and get it coming.

 

[TOHATSU GURU]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

The one in the link.

 

[tineke]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

I was reading this post and loked to the pdf.I also have Tohatsu 5hp MFS5A2 and my local dealer changed only the nozles for 6hp.Bud didnt worked wery well.So I will have to change the carburetor, but on the picture is the air nozzle marked with 1-1-15 and it is not on the list.Am I correct, so if I drill the bronze and then adjust the screw under.Would this be OK?

 

[TOHATSU GURU]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

You have to change the carburetor body itself, so it sounds like nothing was actually done. As to drilling an airjet...To what spec? Without knowing the spec(unpublished) you don't know what to drill to.

 

[tineke]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

Hi again.
Ok on the top of the carburator is one small round jellow cover.I ment to drill this one.Under this cap is one screw on the part list picture is marked with 1-1-15.This one is not changeable but only adjustable.This is the screw for the mix ratio.The guys here are changing the jets and then adjusting this screw under the driled bronze cover.Check on the picture of the pdf attached on the previous post.But as one said before adjusting this screw, remember how it was.So if something goes wrong you can go back....

What do you think.


Tineke

 

[jeremya]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

Hi,

Im from England, and this forum is brilliant.

I have a 4HP/4stroke mariner, and its ok apart from being so heavy.

Did the new carb upgrades work? was it well worth making the changes?

How easy is it to set the carb up??

Would I also need to put a prop on with a steeper pitch?

The master plan is to tune up the outboard, so I can get my inflateable to plane with more than one person in...

Looking forward to hearing some replies!

Jeremy

 

[Ozzy RZ]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

Tohatsu Guru,
Or anyone basically.
Firstly, Hi, I have just got my first 4 stroke Tohatsu motor.
It is a 2010 Model - MFS5B
Serial Number - 040541AX
So, from what you guys have stated, if i buy the MFS6B carburetor, this will make my 5hp turn into a 6HP?

In regards to the New Tohatsu 5hp or 6hp four stroke engines,

Has anyone checked the head squish measurement and flowed the head ? I know that on 4 stroke motor bike engines we run about 0.9-1mm squish clearence to improve compression. And in most cases, most 4 stroke heads can be made to flow better than stock.
Ps, We have 95-Ron fuel at every gas station here in OZ!

 

[TOHATSU GURU]

Re: 4 Hp 4 Stroke Tohatsu Convert To 5 Hp

Yes and yes. But, the tiny, not noticable increase in power is not worth the effort in milling the head.