Topic: Work colleague with cb750 randomly cutting out

[-CB-Jamie-]

OK so a work colleague of mine is having a problem with his 750 K1. I'm hoping somebody here might be able to give me some clues to what might be the problem so I can pass them along to him.

The problem is he can be just driving along and suddenly with no warning the bike just cuts out, as in the engine stops but the bike still has power as the oil light comes back on, what he has to do to restart it is turn off the ignition key and turn it back on and it starts right up. He used to roll to a stop to do this but now he does it straight away by pulling in the clutch and coasting at full speed. It is actually quite dangerous as lately he was overtaking a truck when it hppened.  It seems to be completely random as he said it might happen 5 times in driving half a mile or mightn't happen for a couple a hundred miles.

Some info on the bike:
Its a cb750 K1
Has a Boyer Brandsen electronic ignition
Has a Boyer Brandsen power box
Has Boyer Brandsen coils (I think)
Other than that its stock, intake exhaust etc.
He has also fitted a brand new wiring loom in the hope of curing it but that didn't work.

Thanks in advance for any help
Jamie

[japscrap]

the boyer brandson ignition is the culprit,scrap it.
get a dyna s ignition or go back to a stock points plate.

sounds like a heat short problem .

[MCRider]

the boyer brandson ignition is the culprit,scrap it.
get a dyna s ignition or go back to a stock points plate.

sounds like a heat short problem .

I don't have a good feeling about the Boyer Bransden either, never read good comments.

But it could be the key switch as well. If it was an under tank model that was moved up to the handlebars, as was often the case, they often fail from getting water in them, or just because. Its easier to swap out than the ignition.

Fail = intermittent contact.

[phil71]

Can't be the key, that black wire would kill the idiot lights if it went dead, and he covered that in the OP

[bollingball]

One thing I have learned over the years is an intermittent problem that can not be reproduced can be a bear to figure out. It does seem to be electrical. If it had points I could help so I will defer to the Boyer Boys Maybe there web site has some trouble shooting info. Just because it has a new harness does not mean all is well did he clean every thing that plugs into the harness?

[MCRider]

Can't be the key, that black wire would kill the idiot lights if it went dead, and he covered that in the OP

Electrical stuff is not my forte and I'll defer the technicalities to anyone who claims to know better.

Having said that, the shadretree in me would replace the ignition switch, at least with a loaner, to eliminate the variable and because I don't know any better.   

[-CB-Jamie-]

Sorry forgot to say in the OP he got a new ignition switch for it too, he got the one from DSS.
I dont think it's the ignition switch though as it keeps power and the oil light comes back on with the lack of oil pressure with the engine dead.

My first thoughts too were that it could be the boyer brandsen electronic ignition or power box causing the problem and switching it off and back on just resets something in the unit maybe?? I don't even know what the purpose of the power box is? Also like rotortiller says it could be a contact problem at the killswitch?

[MCRider]

Sorry forgot to say in the OP he got a new ignition switch for it too, he got the one from DSS.
I dont think it's the ignition switch though as it keeps power and the oil light comes back on with the lack of oil pressure with the engine dead.
SNIP

Oops, never mind.