Topic: Mighty Annoying problem 750KO.

[Old Moe Toe]

Lucky for me I have a relatively low mileage 750KO. I have had this bike for about 10 years and it still has that feel of a brand new bike.
A few years ago I fitted one of Hondaman's transistorized ignition units as I was so happy with the one I'd put on my K2750.
The Summer before last I was out on a ride maybe 50 miles into it, going along a highway when the bike just died all of a sudden. The warning lights on the speedo were still working however it felt like the sparks were not getting to the plugs. I did not have any tools, so just had a look at various connections, battery leads, the connectors to Marks ignition unit etc, and could not see anything wrong.
Anyway after a short while I hit the starter button and the bike fired right up and off I went again for maybe a mile or two and then the same thing happened. Again after a wait it fired right up and on I went. Until it happened again and again.
I made it to a friends place, still a long way from home, who had tools and a workshop and I disconnected the transistorized ignition unit and then rode all the way home with no problem.
Once home I double checked that all the connections seemed to be good on Marks ignition unit and re-connected it. Next ride the problem returned many times before I got home. Each time it was wait for some time then the bike would fire up again.
I thought there must have been something wrong with the transistorized ignition unit and sent it back to Mark who tested it and said there was nothing wrong with it, and for good measure he sent me a new unit anyway.
I installed the new unit and before too long the sudden loss of power happened again.
In the end I just gave up and removed the second ignition unit thinking for some inexplicable reason the unit was just not compatible with my KO.
The last few times I have ridden the bike just on the standard points set up there has been no problem....UNTIL TODAY when I was riding along and there was a split second loss of power (like the plugs were not sparking) but the bike picked up again and I kept going for maybe a half mile wondering what had happened when the old loss of power thing happened again. After a while the bike started up and on I went.
Hoping some one can offer some suggestions as to what might be causing this, it is dangerous and driving me bananas, nuts, to drink.
Thanks in advance.
Brad

[RAFster122s]

Not likely an ignition switch failing, but it does sound like a resistive failure, heated joint from oxidation/corrosion until it goes open circuit until it cools again.
I would start with checking all your power feeds and circuits to the coils and points. Disassemble and clean, reassembling with dab of dielectric grease.

[ekpent]

 Or its starving for fuel and in the time it takes to 'cool' the bowls may be re-filling. Be nice to check for a good spark while its having a failure. Hooking an extra spark plug from your pocket to a lead and grounding on the engine might be helpful.

[Don R]

When I have an ignition problem it's almost always fuel related. L0L.  I'm suspicious of the kill switch and it's related wiring and the feed to it. Also on a K0, the main fuse holder is prone to failure due to rubber degrading and/or a new fuse holder too soft rubber to hold a grip on the fuse. I have plugged a blade fuse onto the spade terminals to avoid this issue.
  Has it happened at night when you would notice the lights going out? The entire bike may be blanking out, but you just notice the ignition.

[Old Moe Toe]

When I have an ignition problem it's almost always fuel related. L0L.  I'm suspicious of the kill switch and it's related wiring and the feed to it. Also on a K0, the main fuse holder is prone to failure due to rubber degrading and/or a new fuse holder too soft rubber to hold a grip on the fuse. I have plugged a blade fuse onto the spade terminals to avoid this issue.
  Has it happened at night when you would notice the lights going out? The entire bike may be blanking out, but you just notice the ignition.

You know Don it does actually feel like the kill switch gets turned to the non run position, of course it hasn't though looking at the switch.
I am not game to ride the bike at night where I live as there are so many kangaroos waiting to launch themselves at you however it is not the entire bike blanking out because the oil and neutral warning lights are still working when the problem happens.I will have a look at that main fuse holder as it is still the original 51 year old one.

[ekpent]

 A K1 1971 also has just one single fuse for the system. I had one that was a little dodgy but when it would give a problem all the power was gone.

[Kevin D]

On my own bike, one of the wires to the front brake light switch broke from flexing. It was intermittent and the wire jacket was ok but the copper strands inside were broken.  I replaced the brake light switch wires with super flex meter leads and there has been no further trouble.

 But it got me to wondering about the main harness and if any wire would break in the same manner and how it would manifest, but the main harness flexes a lot less than the brake switch wires,
 So far, there have been no problems like this for me and I have not read any thread where this was the case, and I don’t believe it’s the case here, but s___ does happen, usually to me. Moe it sounds like your problem needs a little temp to provoke it.

For an intermittent wire/switch/connection, I set the meter to ohms, connect test probes to both ends of the specimen, start flexing the wire/operating the switches/ tug the connection and if you have a bad wire/switch the intermittent will appear.

[maxheadflow]

Gas cap vent plugged.

[RAFster122s]

Black wire rot can be a problem with some old harnesses, just haven't heard of it being a problem on our Hondas.

[Don R]

 I've seen a broken in the middle wire on a cb750, a guy on here asked for help and my brother and I rode there and he actually found it with some help.

[Old Moe Toe]

I've seen a broken in the middle wire on a cb750, a guy on here asked for help and my brother and I rode there and he actually found it with some help.

Hmm? Like Kevin D my front brake light wires to switch have played up in the past and needed attention due to the constant movement of the front forks. I will have a closer look at the wiring around there, not sure whether that'd be affecting the sparks though.

[newday777]

For an intermittent wire/switch/connection, I set the meter to ohms, connect test probes to both ends of the specimen, start flexing the wire/operating the switches/ tug the connection and if you have a bad wire/switch the intermittent will appear.

This is very key to finding electrical problems. Over the years I have found bad crimped connectors, bad solder connectors in switches and broken wires in seemingly good wires to the eye. A 12 volt test light is also a good tool to use along with a good multimeter.

[BenelliSEI]

Same symptoms on my K1 a few years ago. Finally traced to kill switch. Put a test light to your coil feed and repeatedly turn the kill switch through all positions. On mine, that revealed an intermittent problem....... Maybe?