4hp to 6hp Tohatsu convert?

Recently purchased a 2016 Nissan tohatsu kicker motor 4hp MFS4CDS

I want to convert to a 6hp by replacing the carb and also put a sail pro prop on it for high thrust.

I’m not sure if I should be buying the 6A, 6B, or 6C carb though.

Thanks

Wouldn’t you also need to change out the exhaust ports?

-J.

I believe only the carburetor is needed.

Do you think its geared correctly to handle the high thrust your looking for?

I believe everything is identical between the 4.5.6 except the carb and props.

Many people do this up grade. I am just clueless on the ABC.

Just found that ABC is model years. Mine is the latest c version so I’ll need the 6C.

Thanks

Fbrm have you used the motor yet? If so how did it perform?

Works like it’s supposed to.

Thanks, that was very helpful. LOL

What do you want to know about it?

It’s a sweet motor. I bought the 4 knowing I was upgrading it to a 6. So this is not a performance thing if that’s what your wondering. My kicker is predominately an emergency return to the landing and it’ll get used lightly for fishing

Just wondering if it vibrates and or shakes a lot due to being a 1 cylinder motor. I was thinking of buying a six horse merc for the same reasons and some trolling.

Yeah it’s going to shake more than a 2 cylinder. Buy you’ll get the weight with 2 cylinders too

Not sure if this is any real help but I believe the tohatsu, Nissan, and Mercury are all the same motors. I believe they are all made by tohatsu. Might open up your part options a bit.

The Mercury is a Tohatsu motor for sure. I don’t know if it is true, but I was told that when I bought a new one in 2012 Mercury puts their own gear case on the pro kicker that has a lower gear ratio so it will troll slower than the Tohatsu, but again it was hearsay. Mine was a 9.9 though. Good motor, but sucked to start when it was colder than 40F.

I did find it hard to start and took a while to warm up this week for the ten minutes of trolling I did on lotw when it was 20°. I’m guessing the bigger carb may help..

Definitely same motor as mercury.

Bump

So I tried this today. The carb upgrade from the 4hp to 6hp connected flawlessly.

The biggest concern now is it sounds like it revs way tooooo high. Any thoughts?

I have a larger prop. Might try that to drive the RPMs down but need to buy a tach to test.

Those tiny tach / hour meter type tachometers work great when messing with props.

And, in a kicker situation it could help with dialing in previous settings easier.

Well…not the best news

Ran the new carb. when WOT, it seems to bog down. My tiny tach is all over the board so I’m not happy or trust it but it does drop in RPMs when WOT. Trying to think of other adjustments needed. It does sound like it’s reving waaaay more. Throttle linkage adjustment? anything else with the carb?

Check the spark plug. White or gray is too lean (needs more fuel). Black or dark colored plug will be too rich. You may need a different size main jet to make these changes. The prope size and pitch should change your rpms.

Final update. GREAT NEWS! I was able to take it out to a lake a few weeks ago and it ran perfect. I’m guessing the motor didn’t like the higher RPM’s in neutral but in gear it worked great.

I was able to get up on plane finally with two adult males and achieved 4 MPH faster speed with roughly 1k more RPM’s.

The myth of upgrading a 4 to a 6 hp motor has been successful!

Thanks for going through the process of figuring it out for us.

Obviously I’ve considered this change

Can you put together the recipe of parts and changes necessary?

@clowncolor

FishBlood&RiverMud wrote:

Thanks for going through the process of figuring it out for us.

Obviously I’ve considered this change

Can you put together the recipe of parts and changes necessary?

1) the easiest way is go get the motor s/n and reference that online. This is easy if you have a Nissan or Tohatsu motor. If any other brand, like me (Mercury), you’ll need to search the Mercury data base (more expensive but you can get around that). The issue is there are A-B-C carbs which correlate to a year range of motors. The kicker here is all the motors (including carb) are made by Tohatsu. So if you have a Mercury for say, you need to look a little further. Mercury will sell you one, but for over $100 then Tohatsu.
2) If you know the year of motor, just search for that years Carb for the Tohatsu brand. I went Thru Defender. I searched 2003 Tohatsu 6hp carb (I currently have a Mercury 4 hp). I did this through 3 different websites and they all gave me the same part number…Mercury Distribution however, gave me a different part number which made me nervous…
3) Order one carb gasket as well
4) You literally unscrew two 4″ (roughly) bolts to take out the carb. No special tools, just a standard Philips head.
4) Disconnect the two black fuel hoses that are held with a hose clamp…simple pliers will do.
5) Just wiggle out the throttle link and choke link you are all set (Reverse all to put back together).

I did upgrade my prop but I had a spare prop anyways and it just so happened I had the correct prop. This is not needed though but may give a just a little more of an edge to plain out your boat if heavy enough. There are three prop sizes and they’ll all work…one may just work ever so slightly better.

I also bought a tiny tach (generic brand) and tested for RPM’s. You simply wrap the end of the cord a few times around the spark plug harness and it will show the RPM’s.

I ran my 4hp carb on a small lake with a buddy and the tach connected. We were around 7-8 mph and around 4500 RPM’s. Brought the boat to shore and swapped out carbs in 5 minutes…it’s that easy! With the 6hp carb, I was able to get the boat on plan and reach 13 mph at 5500 RPM’s. I didn’t see much improvement in speed, other than maybe 1 mph difference but the difference showed when I got up on plane and than she took off!

Hope that helps.

Thank you thank you!