Converting 6 msht outboard to 8hp

[FoothillsGlenn]

I have a 6 MSHT outboard that needs its carb replaced or rebuilt. All engine parts appear to be the same for the 6 and 8 hp models of the same engine, except the carburetor, and the needle valves in the carbs.

In fact, the carb rebuild kit number for both 6msht and 8msht is identical; it is 6G1-W0093-00-00.

Given my druthers, I'd like to boost my hp, so my questions:

- If I order that rebuild kit for my 6 MSHT outboard, will work okay and will I then have 8hp?

- And, if I decide to replace the carb, can I put the 8hp carb on my 6 MSHT outboard, and will that work okay and give me 8hp?

Another curious thing I note is that the carb indicated for the 8msht is about $50 cheaper than the carb indicated for the 6hp, so I'd also like to save $50, if I decide to replace the carb, all other things being equal.

[bajakeith]

6 to 8

LOL..for years I've been saying " when comes it down to motor part prices ,,,they tape a bunch of prices on a dart board,, put on a blindfold and throw a dart" now as to your question .. a lot of pwr heads get used for serval hp's..on 2 strokes bigger ports and carbs.. on four strokes there can be a lot more veribles..cam,,valve size, timing, compression!! just to name a few.. the 8hp carb might fit or might have a slightly larger (wider) stud hole pattern....about the only way is put a caliper on the o.d. of your carb and ask your part man to do the same at his end and make sure throttle pick up is even on the same side of the carb....risky biz IMO.....

[brayhaven]

I have a 6 MSHT outboard that needs its carb replaced or rebuilt. All engine parts appear to be the same for the 6 and 8 hp models of the same engine, except the carburetor, and the needle valves in the carbs.

In fact, the carb rebuild kit number for both 6msht and 8msht is identical; it is 6G1-W0093-00-00.

Given my druthers, I'd like to boost my hp, so my questions:

- If I order that rebuild kit for my 6 MSHT outboard, will work okay and will I then have 8hp?

- And, if I decide to replace the carb, can I put the 8hp carb on my 6 MSHT outboard, and will that work okay and give me 8hp?

Another curious thing I note is that the carb indicated for the 8msht is about $50 cheaper than the carb indicated for the 6hp, so I'd also like to save $50, if I decide to replace the carb, all other things being equal.

I just converted my 6 to an 8hp. I knew I needewd an 8 for my cartop 12' Valco, but couldn't find one. Sure enough the 6 I finally bought was just a little weak. Took a long time to get on plane with 2 people and ran @13mph. I remember when I was a Johnson dealer we converted 9.9's to 15's all the time, by changing carbs & exhaust baffles & figured that was a good place to start.
Looking at all the parts, the only ones that are different on the 8 are the exhaust manifold & carb. Some things never change ). We are trying to move more air/fuel so that makes sense. The manifold has a ring in the 6hp restricting flow and it could be drilled or maybe punched out. I just bought a new 8 manifold. The carb throat is larger.
The conversion worked perfectly, boat jumps on plane now & runs 18+ mph. Cost @ 250 or so. Be sure to get the powerhead gasket & exh gasket.
Some say you can't boost hp by 30% that easy, but remember this was designed as an 8hp and restricted down to 6. You are just removing those restrictions.
Greg

[madharchod]

that's it mate you have the answer replace the carb and you have yourself a 8hp motor ,i have converted so many 80hp to 100hp and 75 to 90hp in my life time this is piece of cake with two stroke its the carby and needle ,and with four stroke its the air restrictor in the throttle body remove that and bingo you have more power

[brayhaven]

that's it mate you have the answer replace the carb and you have yourself a 8hp motor ,i have converted so many 80hp to 100hp and 75 to 90hp in my life time this is piece of cake with two stroke its the carby and needle ,and with four stroke its the air restrictor in the throttle body remove that and bingo you have more power

It must have the exhaust too. Or it won't get the full power. You have to get the air/fuel through the engine. Strangley, the carb jets are the same numbers, in the 6 & 8 hp carbs, but the throat in the 8 carb is clearly larger.
Greg

[Mynottony]

Hello,
I'm new to this forum and boating in general.
Sorry to dig up an old thread but does anyone know if this same procedure would apply to a 1988 6sg?
I would love to get a little more pep.
Thanks in advance.

[brayhaven]

Probably would be the same procedure. That's been the std way to reduce or increase 2 stroke HP output since I was a Johnson dealer in the 70's.
Greg

[BQUICK]

676-14943-19-00
JET, MAIN (#80)
U.R. 6 MODEL

16 676-14943-26-00
JET, MAIN (#98)
U.R. 8 MODEL

No, jets are significantly bigger in 8hp carb. Has anyone just tried the bigger carb on a 6hp? I know it would be better to change manifold also but it still might give a noticable increae in top end power.

[mikedefieslife]

Bit of a necro thread bump but relevant I think.

I came across a youtube video where guy removed the washer in the exhaust. No mention at all about the carbs. Would there be any benefit or problems of only removing washer?

[mikedefieslife]

Started looking at this again after discovering that my 6hp has the exhaust washer removed already.

https://www.boats.net/catalog/yamaha...shu/carburetor
https://www.boats.net/catalog/yamaha...shu/carburetor

The jets for the two different versions 8hp and 6hp are identical at #45 and #98

Two different carbs are listed for each version 6H6-14301-01-00 and 6G1-14301-01-00. Each of the two carbs carries the same part number regarless as to whether it is used for the 6hp or the 8hp.

Other here have mentioned that the 8hp carb has a wider throat. How they have identified that I don't know.

Researching further it is claimed that parts starting 6H represents the 8hp model, whilst 6G is the 6hp model. Having looked at my engine (originally at 6hp model), the carb is the 6G1-14301-01-00.

[boscoe99]

Started looking at this again after discovering that my 6hp has the exhaust washer removed already.

https://www.boats.net/catalog/yamaha...shu/carburetor
https://www.boats.net/catalog/yamaha...shu/carburetor

The jets for the two different versions 8hp and 6hp are identical at #45 and #98

Two different carbs are listed for each version 6H6-14301-01-00 and 6G1-14301-01-00. Each of the two carbs carries the same part number regarless as to whether it is used for the 6hp or the 8hp.

Other here have mentioned that the 8hp carb has a wider throat. How they have identified that I don't know.

Researching further it is claimed that parts starting 6H represents the 8hp model, whilst 6G is the 6hp model. Having looked at my engine (originally at 6hp model), the carb is the 6G1-14301-01-00.

How did you come to the conclusion that the carburetors are the same part number? I am not seeing it. What I see is offered below:
z68.jpg

[mikedefieslife]

Thanks. Boats.net shows the same two carbs for either engine. Where your image is different is the remarks column. That confirms that the 6G is for the 8hp and the 6H for the 6hp engine. What website did you use for the fiche?

[boscoe99]

It is from the Yamaha USA website. www.yamahaoutboards.com

The boats.net website has been fooled into thinking that both carburetors are used on the same motor. They are not.

[mikedefieslife]

I bought the 6H carb and placed it next to my 6G carb. As has been said they are different part numbers. It has also been said that the 6H has a larger throat. I have no idea what the actual differences in the carbs is though.

On both carbs the inlet and outlet measured 21.5mm and 26.5mm. Which part is considered the throat?

The placebo affect of the new carb was nice. Can't really say much more than that.