NS25C2 Fouling Plugs

[nissanduckhunter]

I recently acquired a 1987 NS25C2 It has been sitting for awhile so when I got it I replaced all the fuel lines, the fuel tank and the spark plugs. I am currently running it in a drum of water.

With new plugs it will run great and even idle down really low like it should. And you can run it faster if you gradually give it throttle. However, if you ever just throw the gas to it, it will spit and sputter and smoke like its not burning all of the fuel being delivered. Upon replacing the plugs it will run great again. Thoughts? Thanks in Advance!!

Also, after reading this forum I found out about the NGK BP7HS-10 plugs, I have ordered them and I'm waiting for them to come in. I highly doubt those will fix everything though.

 

[pvanv]

Pretty old model. Make sure the carb and ignition are synced correctly. The BP plugs are better idling, as they have a projected tip. the -10 means they are pre-gapped to 1 mm. Run 50:1 fuelil ratio. Check compression. Clean the carb properly. If the carb base gasket is restricted (with a slot in it instead of wide open), you can run a 30 hp gasket, and adjust the carb to open fully at WOT, and get 30 hp. Good luck.

 

[nissanduckhunter]

Thank you! What do you mean by syncing the carb and ignition? I am a decent shade tree mechanic but I've never heard that term. Are you saying check the timing?

 

[pvanv]

Yes. In the trade, it's called "link and sync". Making sure any throttle stoppers and link arms are properly adjusted.

 

[Sea Rider]

It's a ver bad idea to run any 2 strokes engine on a barrel for long time periods, only good for a short test, impeller check or while flushing the engine if no muffs are available. Even new plugs will be fouled shortly, it's the nature of the beast.

If engine happens to be a Jurassic one, running an overdose of carbon remover product squirted through carb while engine is running would be the way to go, follow can instructions, engine will idel and run much smoother throughout the whole throttle range. Can remove carb air silencer for a much better application procedure.

Happy Boating

 

[nissanduckhunter]

Thanks guys! So with the new spark plugs its the same deal, idles great but once you throw the gas at it, it fouls the plugs.

I have been working by myself so I couldn't hold the spark plug and pull the cord to check spark. I got some help yesterday and noticed that the spark a new plug was VERY weak. I pulled the flywheel off and sanded the magnets, it all looked good under there. I am now afraid that the CDI box will need to be replaced. I checked the voltage going to the CDI box, I was getting between 10 and 13 volts. What is spec? I am just trying to nail down what needs to be replaced. If it is the CDI box, is there a way to rebuild it? I have found prices of about $200.00+, is there any cheaper alternative?

Thanks!

 

[pvanv]

Did you use a DVA meter or oscilloscope to read the outputs from the exciter and trigger coils? That's a MUST. The pulses are so short that an ordinary voltmeter won't catch them properly. That's why Tohatsu specifies using an ohm meter to check them. While the CD could fail, you need to troubleshoot, based on the Factory service manual as a guide first. Otherwise, buy a new exciter (NLA), a new trigger (NLA), and a new CD ($319), and throw money at it.

 

[Sea Rider]

Yep, troubleshoot with a proper DVA meter both upper electrical parts found under flywheel, then the CD and finally the Ignition Coil in that order. Will know which one is the culprit if engine is missing, worse under load while pushing a boat.

Will be good to perform a good internal carb clean if haven't done so before electrically troubleshooting, carbs working in non mint cond will contribute greatly for OB to fail too.

2 strokes OB's don't like to idle or run at very slow fast displacement speeds for long time periods, worse if run in a barrel but loves to be run at full hammer down for long time periods in which plugs stays much cleaner due to having reached their self cleaning temp which starts at + 500º C.

Don't know why the CD unit being so small in size and darn internally simple compared to other larger and probably more sophisticated ones in any other CD brand have sky rocketed their prices. Used to be around 200 bugs some years back...

Happy Boating