NS25C2 Revs Up and Down

[AGENT 37]

I was gifted the subject motor a few weeks ago and was told that it "surges". Well, I gave it a look over, checked compression and found 130 even on both cylinders, tested the kill switch circuitry, and verified spark on both cylinders. I then drained the carb bowl, flushed the lines with fresh, non-ethanol 50:1, started it up and confirmed the issue. It started right up after just a few pulls and ran at a rather higher RPM than expected and revved up and down and stumbled at any throttle setting. The last guy who messed around with it had a hunch the condition was due to a faulty CD unit... Not being one to fire off expensive non-returnable parts at a project motor I decided go ahead and gut the carburetor, give it a thorough soak and cleaning, I scrubbed, sprayed and removed all jets and blew through all passages I could access aside from removing the pressed plugs on the top.

I put it back together, reinstalled the carb, and gave her a test run. Same condition but I noted that I could smooth it out by messing with the choke. I also found that the idle speed was cranked up so I shortened the first linkage from the tiller and backed the idle speed stop out. I trimmed the ends of the fuel lines due to minor cracking and distortion and re-primed the fuel lines to do a more thorough leak test. I noted very light fuel seepage coming from around the float bowl seam, drain plug, and fuel supply hose barb. I manipulated the hose between the pump and the carb to see if I could get it to seal and the output barb snapped off of the fuel pump. Sweet.

Next move was to use a double male barb to connect my tank line to the carb line and see how it would run with the fuel pump bypassed. That was when I realized the fuel leak at the carb inlet was due to a hairline crack in the plastic barb. Sweet!

Both plastic parts on the fuel pump and carb are not replaceable items so I just ordered a new carb, pump, and gaskets for both. Hopefully the breaking of brittle plastic pieces was a sign and I can get this thing going with the two big ticket fuel system items.

I also looked into the ignition system a bit. The weak looking spark had me concerned for a bit but the fact that the motor starts relatively easily and runs on either cylinder kinda throws me off. Is that how these babies are? I don't have a DVA available but I did resistance checks on the exciter (stator) and pulsar (trigger) coils and got the following readings:
Exciter = 333 ohms (spec calls for for 200-300ohms)
Trigger = 40 ohms (spec calls for 30-46)

Would the 33 ohm higher resistance be of concern on the exciter coil?

Anybody have similar experience to share or any words of encouragement to offer?

I fired off an email to Nissan with the model and serial number and they came back telling me it is a 1990 motor. It's blue and grey and in pretty good shape for a 26 year old motor living on the windward side of Oahu. I think it might do my recently purchased 1992 4M Avon Searider well if I can get it running good.

Aloha, ~B~

 

[pvanv]

If fiddling with the choke helps, odds are the mixture is too lean, or possibly a leaky base gasket is causing the mixture to lean out. Since the idle was too high, that may have been to cover up or compensate for incorrect mixture, usually varnishing in the low speed circuit. Previous work on the carb may have damaged that circuit, so that even though you have it clean, it is not flowing properly. The resistance values sound OK. Odds are the new pump and carb will fix it. Install new fuel lines at the same time.

 

[AGENT 37]

Thanks for the boost of confidence Paul, I had the same thoughts about it leaning out. If there's fuel leaking out in multiple spots there's bound to be air getting in. I didn't notice any damage to the carb, not even tool marks on the jets so it's safe to assume that the only work it has likely had done was drain, flush, and maybe cleaning of the fuel bowl. The fuel lines are a little hardened and had some minor splitting on the ends so I intended to replace them as well.

I was given the 25 along with two other "junk" motors and a pile of parts. While I'm waiting for Nissan parts I'll finish up my OMC projects. They're a couple of 1990 15's. I've done a couple carb overhauls, replaced some missing parts and got them both running well... "one pull start" motors in fact. Both outboards were lacking the volume of cooling water that I'd like to see. I already broke one down and replaced the cooling tube supply and discharge grommets with 1000% improvement.

There's nothing wrong with these old dinosaurs, except maybe for the difficulty of acquiring obsolete and NLA parts. I have a for a 1993 Yamaha 40 that hasn't been used in over 5 years because of a cracked tiller handle. I've been looking for a replacement and recently bought the only tiller I've seen on the web. I probably paid half of what the motor is worth... but I guess it's better than having a worthless motor.

 

[Sea Rider]

Bad internal fuel connector orings can give those symptoms, install a new fuel hose. Is prop hub in 100% working order ?

Happy Boating

 

[AGENT 37]

I'm essentially replacing the entire fuel system; carburetor, fuel pump, internal lines, connectors. Prop is serviceable but isn't a factor on this one... I haven't even put the motor near the water yet. (It's that bad)

 

[AGENT 37]

I just installed the new fuel pump gasket, new fuel pump, new carburetor gasket, and new carburetor. I also replaced fuel lines, fuel tank, fuel tank hose, and all fuel connectors. Running condition is exactly the same, no improvement.

I do however note now that the engine is running on the top cylinder only: disconnecting the bottom spark plug has no effect, engine will die when pulling the top. Swapping the spark plug leads produces the same result. Top cylinder fires but bottom will not. Compression on both cylinders is 124psi.

I do see spark on the bottom cylinder with a plug installed and grounded out to the block

Timing is set for 25HP (20deg), advancing to 30HP (25deg) has no effect.

Adjusting the air mixture on my shiny new carburetor does not help either.

 

[pvanv]

Is the lower plug dry? If so, you seem to not be getting fuel. If soaked, seems it's flooded so bad that it can't spark. Try swapping plugs, or installing new ones.

 

[AGENT 37]

Plugs are wet. I already tried swapping them as well as installing new. If the bottom was dry I might consider a reed valve issue.

 

[pvanv]

Hmm. I wonder about either a buildup of oil in the lower crankcase (won't burn) or similar. Could try running a can of OMC engine tuner through...

 

[Sea Rider]

Advancing timing to 30 deg will have 0 effect if that tricky condition is not previously resolved, latter can pass that 25 to a 30 HP. Is Ignition Coil 100% eperative, ok producing spark, but has the right power ? Check with gap tester.

Are you testing that OB on a barrel, muffs ? Have you pulled flywheel off ? Magnets (2) should not be broken or missing ? Is Exciter Coil surface clean, not heavily rusted as to produce less electric current ?

Happy Boating

 

[AGENT 37]

I've been running the motor on muffs. I'm assuming you are referring to advancing the timing to 25 deg to get 30HP. And I agree, it won't make any difference if the motor isn't running right to begin with.

I don't have an analog DVA meter available for testing, but I've got a couple varieties of Fluke meters available to borrow. I'll do some research to see if what I have access to is appropriate for ignition testing. Same goes for the flywheel puller... tools available are limited. I tried wedging the prop with a piece of wood and breaking the crank nut free but the wood kept slipping out of position... No need to round out corners on the flywheel nut. Maybe I'll try a foam crab pot float for a wedge instead.... I'll get back to you with results on the ignition component conditions when able. ( I do have torque wrenches to reassemble)

The motor came with NGK BHS7-10 plugs installed. I'm trying to locate some resistor type plugs locally to install instead, I don't know how much difference they might make, but the BRHS7-10 is what's called for..... maybe there's enough current getting fed back through the ground to the CD unit to cause misfire, but I'm not going to hold my breath for plugs to fix it.

The previous owner had a cheesy Seloc manual for this motor that I've already found information in regarding timing that didn't jive. I don't know how much better a factory Nissan manual would be, but I've not at all been impressed with parts diagrams I've found online from the manufacturer. The info you guys and others have made available on iboats and the rest of the web tends give me confidence to work through however.

One thing I can say is that I feel committed at this point because the motor was free, it is in good shape cosmetically and mechanically, and I just invested good money into a complete fuel system overhaul.

My troubleshooting plan from here consists of:
- Install correct spark plugs
- DVA test pulsar and exciter coils
- Resistance test secondary coils
- Pull flywheel and check magnets and coils surfaces
- Check reed valves
- Replace head gasketa

I'm wondering if it is just not getting signal to fire the bottom cylinder at the right time. There is spark, but if it only happens at the right time for the upper cylinder there's probably something amiss between the flywheel and the CD unit.

Brake parts cleaner makes a pretty good engine tuner right? (-;

 

[Sea Rider]

Can use B7HS-10 or BR7HS-10, second with resistor if using electronic gadgets on board, if not, BH7S-10 will work same, just gap tight to 1.0 mm. Ignition Coil fires both plugs at same time, (2 sparks per revolution) if one side isn't firing right as it should, or firing way low there's the culprit, Don't mess with reed valves, has nothing to do with tricky performance, the issue seems is electrical component related. If CD is faulty, Ignition Coil won't fire plugs right or fire erratically, but should fire even if IG has both internal coils 100% operative.

If would start by :
-Checking under flywheel, if all ok
-Change Ignition Coil
-Change plugs
-Retorque cylinder head to 30 NM (Newton Meters)
-Retorque Intake Maniflod by hand till bolts doen't go any further, don't over tight.
-Test at open water, 2 strokes OB's doesnt like running on muffs at idle/fast idle for long time periods.

Use proper carbon remover as Power Tuner with OB on, follow can instructions, after tricky behaviour has been solved not before, worst on muffs as you need to accelerate OB to higher rpm in order to squirt product through carb to make its way inside and start cleaning.

Happy Boating

 

[AGENT 37]

This evening I re-conducted resistance checks as follows:
Exciter Coil Resistance: + on red exciter lead / - on black = 334.6ohms (spec 150-375)
Pulser Coil Resistance: + on blue pulser lead / - on black = 33.3ohms (spec 23-58)
Secondary Coil Resistance: + on spark plug lead / - on black out of CDI = 2775ohms on one and 2681ohms on the other (spec 3075-7625)

So I'm looking at 1k less resistance through the spark plug lead to the CDI neg/ground that the min value. That points me toward a insulation breakdown in the CD module, which might explain plugs producing less than optimal spark.... just enough to fire one cylinder sporadically.

The R type spark plugs I installed actually seemed to make it run worse, which would probably coincide with the above mentioned state of continuity.

I also popped the flywheel off and found all components to be in place, intact, and factory-shiny new. I also happened to come across an invoice wedged in the service manual for exciter and trigger coils that were purchased in 2012.... I have no idea if the motor ran after those were installed.

On a side note: It would have been nice to recognize sooner that the crank nut is reverse threaded. I managed get it so tight that I slightly mangled the prop with a wedged piece of foam and wood and also broke the output nipple off my brand new fuel pump with a cargo strap that slipped as I was using it to hold the flywheel.

If it weren't for bad luck, some of us just wouldn't have any luck.... today's setbacks were merely a lack of attention to detail and patience however.

I still don't have a DVA adapter. I'm hesitant to buy one because I have never ever had to use one before and Murphy's Law says I won't use it again if I buy it.

 

[Sea Rider]

Bear in mind that all electrical components behave different when cold and warm, OB could experience a heat build up on any of them and misbehave while OB is ON, measuring cold is no indication that component is working spot on as could vary their spec when hot. It's near impossible for CD to fire just one plug, CD has 3 conditions : works ok, electrically misbehaves or is KO, kaput. Ignition Coil is what fires both plugs at same time. A pity you have spent so much money troubleshooting that OB with no avail, buy a new IC and see what happens. Retorque what's been indicated.. Good Luck..

Happy Boating

 

[AGENT 37]

I forgot to mention that I did a torque check the bolts, none broke torque.

I went by radio shack today and picked up a fistful of diodes, resistors, and capacitors to make my own DVA (adapter) and tested the coil outputs with a Fluke meter using the min/max function.

The exciter coil put out 286 VDC - min specification is 100 VDC
The pulser coil put out 13.5 VDC - min specification is 3 VDC

No maximum peak voltage reading is listed on the supplement I have, so I'm going to say that the very strong readings I obtained are probably good.

The CD is firing both plugs when they are placed up against the outside of the cylinder head, but I think that the charge may be frequently finding the path of least resistance to ground internally, through the CD ignition unit, instead of jumping the spark across the plug gap. For whatever reason, the bottom cylinder seems to almost never fire... or it may be firing occasionally, initially making me think the engine was revving up and down.

To paint the picture, this motor is equipped with a CD ignition unit with an internal coil. There are three wires : red, black, and blue going from under the flywheel to the CDI box and two spark plug wires coming out of it, a single wire to ground on the engine block, and the two kill switch wires. There are no unused wires coming out of the CD ignition unit.

There is an unused yellow and unused white wire from under the flywheel. I haven't investigated to see if the circuit is for charging or tachometer hook up.

I'm considering taking a dremel tool to remove the potting from the CD ignition unit, openening it up and seeing if I can clean and re-solder connections. Otherwise I think my next logical step is to get a new CD ignition unit ($300 shipped). I figure I might as well rip the guts out of this one and see if I can stitch it back together first. I know that others before have found success doing this with dirt bikes and such.

 

[AGENT 37]

Well, opening up the CD ignition unit didn't work out quite like I had hoped. It's fully potted so there's no dremeling away around the edges and popping off the protective layer on this one. No reason for me to hem-haw about ordering a new one now.

(I might have hammered on it a little once I realized it was a lost cause)

 

[AGENT 37]

Here are some of the other components of discussion:

 

[Sea Rider]

So this is a single CD/IC unit, right ? if so, much different that the actual 25C3 which is a dual independent component. CD units are very trick to open up and repair, most are solid state and sealed in hard plastic, bakelite, only extreme patience and good disposition will surely make the trick.

Happy Boating

 

[AGENT 37]

Yep, it's been a NS25C2 the whole time with the single CD ignition unit And I agree, the CD Ignition unit is pretty much solid state and not a serviceable component. I don't care how much patience or good disposition one has, I don't think it can be physically be opened up without damage. Perhaps a specific temperature or a chemical compound are the key to gaining access, but never a dremel tool.

So I'm down to ordering a new CD Ignition unit for it now. The images I see for the replacement that is available appear different from what I had on this motor. This one was mounted using three of four mounting holes. The superseding parts appear to be smaller and have only two mounting holes. They do however have the correct wires coming out of them.

There are two part numbers listed for the NS25C2 CD Ignition unit depending on what parts schematic you look at:
3A1-06260-2 is listed under the "old magneto" diagram for the NS25C2 (this diagram looks like what I have)
3A106-2600M is listed under the other 2002 and earlier NS25C2 diagram (this diagram is indiscernible)

What do you think of the 13.5V I obtained from the pulser coil, does that sound typical? I was surprised it was that high.

 

[AGENT 37]

This is what it had:


This is what the superseding part looks like: