# Modifying a Tohatsu M40D



## Rabbitdundied (Feb 2, 2014)

I am new to forum. I am looking for information on what options I have to modify my M40D Tohatsu. It is used for duck hunting and fishing mainly. On the rare occasion I have to boat race to a duck hole therefore this is the need to be faster. It is mounted to a CMC 130 on a 16' semi V aluminum boat. I am currently running a 14p Vengeance Prop. The boat normally runs with a moderate load. 2 guys and say 120lbs of decoys, guns etc. I say this to say that putting a 16p prop that will get me 1 MPH on top end won't help because any advantage will be lost trying to get out of the hole. 

What I would like to know is what options do I have to upgrade the motor? Carbs, reeds, exhaust tuners or anything I may not be considering?


----------



## Lil' Blue Rude (Feb 2, 2014)

think these motors have different carb then the 50hp so you could bolt on a set of them, or there might be a restrictor plate behind the carb. If that's the case all you'd need to do was remove the plate and install 50hp jets. Add some fiber reeds like Chris Carson's or TDR's. You can always shave a bit off the head to get compression up to around 145psi-150psi. probably .015"-.030" would be a good place to start. Make your own tuner. If it's rope start have the flywheel lightened by removing the ring gear. Then if you want to get wild start porting, add some finger ports.


----------



## Rabbitdundied (Feb 2, 2014)

Excuse me for ignorance but what is a tuner? I have heard people mention exhaust tuners but I have no clue what to build or even where to look.


----------



## Lil' Blue Rude (Feb 2, 2014)

Exhaust tuner. The exhaust system for the motor in the mid sections. Most are a straight shot down with no taper or flare. Most people that build a tuner make them like a cow bell. smaller at the top bigger at the bottom, most are square. Most are 7"-9" long depending on what your wanting. Longer tuner has better bottom end and shorter has better top end. Look up a tuner for omc sst60 and you can look up hydro tec web site and check out the tuner for a 40-50hp Yamaha since those motor are some what similar. That will give you an idea about them. Most people around here get a tuner shaved head and carb work done. You'll have to rejet your carb if you build a tuner for it.


----------



## Rabbitdundied (Feb 2, 2014)

Thanks for the explanation and 
telling where to look. I assume a tuner is similar to a tuned pipe
on a motorcycle. I also guess that since you are suggesting I build one that is something that cannot be bought. Any suggestions on jets?


----------



## Lil' Blue Rude (Feb 2, 2014)

Yeah they're like a tuned pipe except they only draw gas out where a tuned expansion chamber would draw gas out and before the port closed again it would stuff part of the charge back in. I wouldn't have a clue what size jet to go up to. When I've done tuners on mine I've went up 2 or 3 sizes. You might want to go up more then that and just check your spark plug color and keep leaning it out until you get that nice light brown coloring. But I'd at least go up 3 sizes starting out. Hydro tec might make you one. Not sure if they would or not.


----------



## Rabbitdundied (Feb 2, 2014)

Thanks again. Ever hear of someone using 70 HP Yamaha Carbs?


----------



## Lil' Blue Rude (Feb 2, 2014)

yeah read that certain models bolt up with little to no modding and you'll have to rejet.


----------



## Rabbitdundied (Feb 2, 2014)

I just went to look at hydro tech website. I wish there was a site like that for Tohatsu/Nissan. Sweet stuff. The tuners I saw look like they are larger at the top and get smaller at the bottom.


----------



## Lil' Blue Rude (Feb 2, 2014)

The larger side was the end where the exhaust dumps out. They have them setting up side down from how they would mount on your motor in the pics.


----------



## Rabbitdundied (Feb 2, 2014)

Ok that would makes sense as to not cause back pressure.


----------

