M40C with electrical issue

[nova_gts]

My Tohatsu M40C has not been running correctly so I have been trouble shooting it myself but think I am just skilled enough to be dangerous. I wanted to see if anyone had any suggestions before I bring it into a mechanic for repair.

Boat - 13' inflatable cat (Seawolf) with brand new SS 11P semi cleaver prop

Issue - My motor is lacking power and not achieving top speed, I put a tach on and when running to the top plug it was not even getting a solid reading. I put it on the bottom plug and am showing WOT about 3700RPM. The motor is sputtering bad and if you look in the carb at WOT you can see it pulsing (I have a video if needed)

A few additional details, the compression is good, around 130psi on both cylinders, carb was recently rebuilt, tried new plugs, and after running I am seeing a lot of unburnt oil from the exhaust.

My conclusion - it is something electrical related, most likely running on 1 cylinder

So I went off the manual as best I could to try and run the pulser coil test and ignition coil test.


Pulser coil (assuming i preformed correctly) was giving me a reading of 21.5 ohms which according to the manual is not in spec

Secondary Coil (again assuming I preformed correctly) I got 2.57K ohms on the top plug and no reading off the bottom.


Please let me know your thoughts.

 

[Sea Rider]

Get a plug tester and check both sides, if one is bad giving very low spark you have an Ignition Coil failure for sure. Buy a new one and replace.

If correctly propped while lightly loaded, that OB should rev around max 6 K wot revs. You're just achieving slight more than half of its max...

Happy Boating

 

[nova_gts]

Thanks Sea Rider, I was actually just looking at the parts diagram vs whats on my motor and I don't have a round Ignition coil as is shown. My plug wires come directly out of the CDI ignition box.

 

[Sea Rider]

Gee, only 2 possible culprits Pulser Coil and CD/IG power pack. Never have had issues with pulser coils going bad but electrical issues with that kind of one piece power pack. How old is that 40 of yours ? Before waisting money sending OB to be checked by a mechanic would buy a new CD/IG pack and swap old one with, that should spring back to life that 40. Once ok check max wot revs achieved with that semi klever 11 prop.

That 40C must be really an oldie, newer ones have independent CD & IG electrical components. Probably one piece power packs could be NLA, which would be very bad news.

Happy Boating

 

[nova_gts]

So the PO told me he thought it was a 96-97 but maybe he was wrong. Is there a way to tell the year?

Yeah that was my fear as I was looking on the parts websites. Is it possible to update grade to a new style if such is the case?

 

[pvanv]

Your motor is probably from around 1992, but could date back to the 80's. It has a trigger coil, exciter coil, and CD with integral ignition coil. Both cylinders fire at the same time, with a "wasted" spark on exhaust. Sounds like the upper plug wire is not firing well -- or maybe not at all. I would inspect both plugs to determine whether the upper plug is in fact not firing. Odds are the exciter and trigger are OK, or both cylinders would likely be acting up. The original Part 346062602 was superceded to 3A1062402M CD with integral coil, has an MSRP of over $319, and requires two plug caps 99998SPCAP1, available separately, for about $6 each. You may be able to convert to the later style of CD and siamese coil, but you may not like that cost, either. You can call Tohatsu America at 214 420 6440 and give them your serial number. They should be able to tell you what parts are still available.

 

[nova_gts]

That's great info, thank you! I didn't get a spark plug tester yet, but I just pulled each plug and pulled the motor a couple times - the bottom plug did appear to be sparking much more frequently than the top plug.

 

[nova_gts]

Ok, so I Just ran 2 tests.

The first one was with a Plug tester light - it didnt work so I'm returning that.

The second and most telling - I started the motor and then proceeded to pull the top spark plug wire, the motor didn't run too much worse. Then I ran it and pulled the bottom plug wire, the motor quickly died.

 

[nova_gts]

do both wires pulse at the same time? in other words can I reverse the bottom and top wires, preform the same test noted above and see if the bottom dies that time?

 

[Sea Rider]

If reversing wires will achieve same result. To troubleshoot spark correctly need a spark tester that can vary gap to check IC strenght when spark jumps.

Happy Boating

 

[nova_gts]

Ok, I got a new CDI with internal coil in. The unit its self came with 5K ohm spark plug resistor caps (according to the Tohatsu tech, they didn't used to come with them, but they do now). So the Plug caps that Pvanv recommended (and are listed to be used with the unit before they started to include them) are 1K ohm caps. I also notice that Tohatsu recommended two different Plugs a BR7HS-10 (plug with internal 5K ohm resistance) and a B7HS-10 plug (non resistance).

My question is what combination should I be using, or what is the desired total resistance? It would seem to me 5-6K ohms is the magic number.

 

[Sea Rider]

Use OB with new CD unit and delivered plug caps, can use any of both posted model plugs. The resistor BR plug will perform better with electronic gadgets on board. Both models needs to be electrode gaped tight to 1.0 mm.

Happy Boating

 

[nova_gts]

Alright well I;m out $320 - that didn't fix it. I want to get the flywheel off to replace the exciter and pulsar. Any way to do this with out the unavailable over priced tool?

 

[Sea Rider]

Is OB having the same exact symptoms as before ? did not get any better ? Without a flywheel extractor near impossible to pull flywheel out. Don't bang with hammer flywheel side trying to loose it once nut is removed., inside glued magnets could break in pieces and that will be the end of that flywheel.

Once flywheel is out, check if pulser coil, exciter magnet side are rusted, oxidized, could not be producing the right amount of electricity for new IG/CD not to work as it should. Clean and file them gently to a smoth cond. Take combo, OB or powerhead to a mechanic, OB shop and have that flywheel removed professionally.

Happy Boating

 

[nova_gts]

Yes, same symptoms, no improvement.

Will an automotive style puller not work?

 

[pvanv]

OK, so you did not actually test the CD, exciter and pulser, and just bought a new, expensive CD on a whim. That's by far the most expensive way to repair an outboard. It's possible you still have another out-of-spec item. Did you check compression yet? Mas the carb been cleaned yet? It's entirely possible that the ignition was Ok from the get-go. But I digress. Yes, a small automotive harmonic balancer puller may fit the flywheel. DO NOT use a puller with hooks. Only use one that pulls via bolts. DO NOT hammer/tap on the rim of the flywheel to "help" it come off.

 

[Sea Rider]

According to OP

"The compression is good, around 130 psi on both cylinders, carb was recently rebuilt, new plugs" He did test, but used a wrong digital meter.

Was mentioned that OB seemed running in 1 cylinder, that's why went for a new IC/CD unit. If would have been just a single Ignition Coil, that would have been the direct culprit. Once flywheel is out check both pulser and exciter physical cond, afterwords check them electrically speaking with a analog meter that reads DVA volts to check if in opt working state.

Anyway, if plan keeping that nice 40C, it's good investment although costly to have at hand a new IC/CD pack if current one proved to be OK, you never know when old stock parts will be NLA. For my peace of mind and constant boating fun, always stock costly electric components myself, for me It's money well spent..

Happy Boating