I purchased a Nissan parts catalog on eBay that detailed the NS40D2 and NS50D2. After reviewing the catalog in detail I determined the NS40D2 is a detuned NS50D2 block and the only difference between the two models is:

1) Carburetors (larger barrel and jets and butterfly opens fully on the 50 hp model)
2) Intake manifold (larger holes to match larger carburetor barrels)
3) Reed valve assemblies (turns out the only difference here is the plates that limit how far the reeds can open - plates allow reeds to open farther on 50 hp model)
4) Air silencer (larger holes to match larger carburetor barrels)
5) Throttle cam (different shape to open butterfly fully on 50 hp model)
6) Spark plugs (BR8HS-10 for 50 hp model vs BR7HS-10 for 40 hp model)
7) Timing link length adjustment (same part but adjusted shorter for 50 hp model and thus timing is more advanced compared to the 40 hp model)

I had concern that the engine block porting might be different between the NS50D2 and NS40D2; however, I confirmed with Tohatsu directly that the blocks are the same between the two models and that the only differences were in fact 1 thru 7 above

It costs about $800 to purchase the parts new from Tohatsu and many of the parts are no longer available; however, I got lucky and found them used locally for $300. I also purchased a carburetor rebuild kit for $100 and I was able to sell my old parts on eBay for about $250 so my total cost was $150 - not bad for a 25% power upgrade.

Also important for the project was the purchase of a service manual for the motor. The most important data this provided was information about factory settings including timing and mixture settings.

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Date: 08/31/14 - 10:12 AM
Added by: wlagarde
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