No spark on an old Honda engine

[Nope.]

Okay, so this isn't strictly a motorbike, but I thought I'd ask the BCF font of knowledge before I start pulling my hair out.

I've got a Honda BF75 7.5hp outboard powerhead in my boat attached to a Volvo Saildrive (if you don't know what that is it isn't really relevant).

The Honda engine is a little two cylinder four stroke from the mid-80's. It uses points ignition. Now, I haven't touched a set of points in 16ish years and TBH I could just do with some advice so I'm not stabbing in the dark and wildly parts swapping.

Last weekend on Sunday the engine started and ran great - no issues. Even started twice. All fine and dandy. On Monday it wouldn't start at all. Didn't even try. Ended up figuring out that it has no spark.

Tracing the wiring, I'm a little confused by how its setup. There is an inline fuse in the ignition circuit that goes somewhere which I found to be blown. I replaced this but it made no difference and hasn't blown since.

-I've checked the resistance values of the coil and all seem within spec.
-I've replaced the plugs.
-I've checked the continuity of the wiring as best I can.
-I've checked the points and found the gap to be far too small (though there is weirdly no specified points gap for this engine, I googled and found a forum post mentioning 0.3-0.4mm) so I adjusted it within spec.
-I've taken off the flywheel, cleaned any rust off of the magnets, and made sure the wiring to the exciter coil & pickup coil (I think that's what they are) is in place.

After this, I'm a bit stumped. I'm slightly confused by what should be happening, which probably isn't helping. Am I right in thinking that there should be no continuity between the two sides of the points until near the top of the ignition stroke? The points are located under, and driven off of, the cam shaft sprocket, which means there is no separate distributor to adjust the position of. It also means they can only be accessed at that point in the engines stroke.

Basically, any advice for diagnosing no spark issues with points ignition systems would be appreciated. I haven't yet measured the resistance values of the coils under the flywheel which I probably should do. I've ordered new points & condenser just in case, but these look like a real pain to fit. Very open to ideas!

Thanks in advance!
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Former: Derbi GP1 50, Sachs XTC 125, Suzuki GSXR 400 GK73A, Kawasaki ZX7R, Suzuki DR250, Yamaha RD350
Current: 2011 Yamaha XT660Z Ténéré, 2003 Yamaha YZR-R1 5PW (In Build), 2009 Kawasaki ZZR1400

[WD Forte]

I know SFA about your Honda engine but have recently been
checking over a mates Johnson outboard with no spark
The seller said it needed a new coil but the coil and source coils metered out just fine

I did find the kill switch was short all the time even with the lanyard toggle in so that was never going to spark

On this 2 cylinder 2 stroke Johnson, the kill switch shorts ignition source power to ground when closed thereby snuffing the sparks.
If yours has a kill switch, check its open with the toggle in and short when pulled out or at least goes into two different states
LO-Hi or HI-Lo
I suspect the CDI box has failed too btw

These lanyard/toggle switches are supposed to be attached to the driver so if they fall overboard, the toggle gets pulled out, the switch closes and the engine stops.

My current theory on the Johnson is that as the engine is 20 years old and the spring loaded plastic rod has been under stress for a lot of that time, it has stretched a millimeter or two and no longer opening the contacts.
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bikers smell of wee

[WD Forte]

That looks like a starter motor bottom left with possibly a regulator
just above it
is that right? does it have a battery too?
If so I'd guess the two coils are one for ignition power and one for charging
Checking their resistances would be a good start.

If my guess is right
The charge coil will have relatively low resistance with thick wire
say 1-2 ohms
The ignition coil will have thinner wires and be say around 400 ohms

More higher resolution pics from various angles would help too
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bikers smell of wee

[stinkwheel]

File the point contacts. A very small amount of contamination or corrosion can prevent a proper contact. You can use a points file if you have one because that's what they're for or a piece of emery cloth/wet and dry. I generally use a bit of wet and dry, I grip it in the points with them closed and pull it back out a couple of times for each contact.

Worth giving them a clean too in case any oil has flung off the cam from your felt or there were traces of oil on your feeler guages. Fun fact, brake cleaner spray DOES leave a residue which is non-conductive so only clean them with electrical contact cleaner or isopropyl alcohol.

If points are being powered up and your kill switch is operating properly as per WD Forte but still no spark, suspect the condenser. Just replace it. It doesn't HAVE to be mounted next tp the points, the electricity doesn't care and it's sometimes easier from a servicing and fitting point of view to fit it next to the low tension side of the coil.

On a lot of basic engines, the only adjustment is the points gap. If the gap is right, the timing is in the correct ballaprk. If they are worn, the timing will be out when the gap is correct. There's a balance to be made between timing and points gap, I'd go for a wrong gap over wrong timing but if they are too worn to get both in the right ballpark, it's new points time.

Yes, there should be an open circuit between the two parts of the points when they are open. Usually the fixed part has continuity with earth and the moving part is isolated from earth unless they are closed. There's usually an arrangement of plastic washers/shims isolating the two parts of the points. I've also seen the spring (which is usually on the moving part) arc out to the housing on occasion.

In most setups, you can simply measure continuity between the single wire running to the points and earth to check points function rather than having to measure directly on the points themselves. I find an analogue meter is best so you can watch needle deflection.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Nope.]

[WD Forte]

Yes it will run with a battery as one of those coils provides the power to the coil which in turn is triggered by the points opening
the charge coils only do that, 'charge' and run independantly of the ignition.
Same as many bikes of that era

What you need to do is find which one is the source coil as described above and test the resistance, say 400 ohms or so
if that checks out test the coil primary and secondary windings
typically 2-3 ohms primary and 8 kilo ohms secondary
if that checks out test the capacitor(condenser) hasn't failed short to ground
you can run it without one for short time just to test its not pulling power to ground
then check the points are shorted ground off the cam
and open circuit when the cam on the crank lifts them open

thassit

BTW my diagnosis on the Johnsons problems proved correct
and its a runner now, its churning water like a good un in
a bathtub out the back
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bikers smell of wee

[doggone]

We just fixed a lawnmower with similar cut out switch like dead man's handle, after spending most of an hour finding no spark then suspecting the switch or wires it was just the cable had stretched. We bent the prong it attaches to on the handle as a cheat to shorten it 1/4 inch actual fix time about two minutes.