Nissan 2-stroke 25HP converted to 30HP timing

[pb9714]

I've recently removed my restrictor plate from my 2005 2stroke NS25C3 to convert the motor to a 30HP. I was told that I needed to adjust the timing as well. Can anyone help explain how to do this on this outboard without suggesting I get a NISSAN service manual. I'm very familar with timing adjustment on V8 engines as I have built several from scratch in my old drag racing days. I have never messed with an outboard until now but it shouldn't be to hard. Any help would be appreciated. Also I've took a photo of what my linkage looks like at WOT. The plastic roller goes past the grove to the end of the arm.

 

[Sea Rider]

Welcome to Iboats,

You have already a converted 30 HP, the roller passed cam groove and achieved a flat widely opened butterfly

Happy Boating

 

[pb9714]

Can you explain how the timing is related to the carb butterfly being wide open?

 

[Sea Rider]

Those engines have 2 stoppers located side of engine at near block extreme which limits the throtttle advance at idle and wot. The upper one called A stopper is usually set at a locking position in which the white roller stops on cam's groove, that's at 20 deg giving aboot 80% of wide open butterfly in comparison to 25 deg achieved when roller passes groove and stops at almost end of cam giving 180 deg opened flat butterfly. It's just a stopper play and carb gasket to detune or upgrade any 25 to 30 and viceverse as both blocks happens to be same CC including carb model.

Have always wondered what difference in rpm, max speed could be achieved if testting same engine with 25 and 30 carb gaskets provided that both runs at 25 deg fully opened flat buttefly, probably just bare minimum. Will need and induction tach, GPS and wot trial to check that..

Happy Boating

 

[Sea Rider]

Sorry double post, system going insane again....

 

[pb9714]

Here are my results.

With the restrictor plate installed and a Solas 13 pitch stainless prop i was maxed out at 4850 RPM at WOT. I installed another Solas 11 pitch prop and removed the restrictor plate and the results are 5800 RPM at WOT and 32 MPH on the GPS. The boat now launches out of the hole and gets on plane very fast unlike before. Im sure the prop was a big change but the engine opens up a lot faster with the restrictor plate removed.

By the way, i have the Solas 13pitch prop for sale. Its practically brand new. I bought it off this site in April this year. I will ship it if someone is interested.

 

[Sea Rider]

Great improvement, restrictor plate, less pitch prop way to go makes the whole performance difference. Years back used to adjust timing advance to 25 deg on detuned 25 HP same Mariner engine which were delivered with 20 deg timing advance. Using same standard prop, worked much better than before, no induction tachs were available at that time to check for spot on prop pitches. Thanks posting for the record. Enjoy a fast boat with roaring engine at back transom..

Happy Boating

 

[csmoczygemba]

Here are my results.

With the restrictor plate installed and a Solas 13 pitch stainless prop i was maxed out at 4850 RPM at WOT. I installed another Solas 11 pitch prop and removed the restrictor plate and the results are 5800 RPM at WOT and 32 MPH on the GPS. The boat now launches out of the hole and gets on plane very fast unlike before. Im sure the prop was a big change but the engine opens up a lot faster with the restrictor plate removed.

By the way, i have the Solas 13pitch prop for sale. Its practically brand new. I bought it off this site in April this year. I will ship it if someone is interested.

hey there, about to do the same thing on my engine. on that solas prop....what is the diameter you are using? I have a little aluminum prop on my motor now but will move up to SST as soon as I can get the rest of my little projects sorted(Tach, Temp Gauge) etc.

 

[pvanv]

Diameter on these is of little influence. Pitch is the biggie. Solas props are king on these; stainless, while slipping less, usually requires less pitch, costs a fortune, and really doesn't pay.

This post is half a decade old, so you should really have started a new one...