Nisssan ns25c2 throttle cam question.

[PeteyD]

I have an early 90s 25hp 2 stroke ive been tweaking with to get the most performance out of it, it runs well ive just ordered a Hardline tachometer to see what my rpms are doing and go from there. In the meen time i have a question about the throttle cam on the carb, i have the timing set up which is straight forward, but i tend to over analyze some things heh. Setting the reverse and start marks is also straight forward, but im curious where the roller on the cam should be when at WOT. Then again this is probably a moot point because ultimately the propeller is what governors the RPM.

 

[TOHATSU GURU]

Re: Nisssan ns25c2 throttle cam question.

Does the service manual say anything about where the roller should be at WOT?

 

[pvanv]

Re: Nisssan ns25c2 throttle cam question.

Yep, get a Factory service manual and have at it. You are aware that the 25C can be upgraded to 30 hp by changing to the 346020111M carb gasket, right?

 

[PeteyD]

Re: Nisssan ns25c2 throttle cam question.

I do have a service manual it dosnt talk about what position the cam should be at WOT, there is however a small indent which i have been assuming is where it should be. No i had no idea that changing a gasket can increase the horsepower heh, how does that happen?

 

[Sea Rider]

Re: Nisssan ns25c2 throttle cam question.

Some Tech issues :

-If comparing a 25C2 to a 30C2 you will find that at full throttle the butterfly on the 25 opens just 3/4 and full butterfly on the 30 model. Both posted pics corresponds to Tohatsu 25C3 & 30A4 HP 2 strokes models which are the newly updated version of both C2 previous models, the difference is that you don't have a middle cut on C2 throttle cam, but both 25 & 30 rollers stops at different cam travelled distances.

-The timing on the 25 is set to 20? and 25? on the 30. If you have a fully opened butterfly on the 25 all you need is a carb gasket swap as recommendd by Paul to pass it to a 30 HP. If set at 20? which is it's factory delivered setting you need to advance magneto timing to 25? for the butterfly to fully open as seen on pic 2 + carb gasket swap.

-If factory set to 20? a carb gasket swap alone won't turn a 25 into a 30. Need to advance magneto timing + 5? in order for the carb to have a fully opnened butterfly (more fuel in) the 30 gasket has a wider mouth compared to the restricted mouth of the 25. + Air + 5? timing does all the updating simple trick.

Told you guys, detailled updates procedures and pics are not shown in service manual as it has been found by Petey D ....he who laughs last, laughs the best!!!

Happy Boating

 

[PeteyD]

Re: Nisssan ns25c2 throttle cam question.

Thanks Sea Rider I guess il get that updated gasket and bring the timing up to 25.