Re: 78 cb750K won't fire up. (1 coil fires other doesn't)

Posted by mitchberry on Sep 08, 2010; 5:16am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/78-cb750K-won-t-fire-up-1-coil-fires-other-doesn-t-tp1425305p1437301.html

hey thanks!  

yeah, basically, the yellow wire will fire either coil that it is plugged into, and the blue wire is 99% dead... it shows a faint voltage...  like.. less than 1v most of the time but not a complete 0v..

i guess it would help if i posted a wiring diagram here but, i have no idea where the wires get their juice from...

they literally only go from the points to the coils... and the condensers plug in opposite of where the points do on the same side, and nothing else goes into the condensers..  it really makes absolutely no sense... at least on my suzuki's there are multiple wires on the condensers, and one is power in, and the other is power out to the points, coils and all that stuff....  

There are only 2 wires on the coils... a black/white one and then either the blue or yellow depending upon the coil... the black and white one is grounded to my knowledge..

this isn't the exact diagram i've been working with, BUT... it is the same in the places that matter...

as far as what happens when i unplug the oil light, basically, it just goes off.. nothing more or less..

 where i do have a problem though is that i have to connect the black/white wire with the black wire in the headlight bucket or none of the 4 coils spark..

 said wires are going to the off on off switch on the right grip... so i assume it's bad.. since then, i pt a bead of solder in it, but that didn't seem to work...  



seriously though.. if you look at this,

 you could literally unplug the black and white wire, and pull the coils and points completely out of the loop there... the only thing i can think of is that the black and white wire gives the coils power.. but it IS as far as i know, a dead / grounded wire.........

 maybe not?"???   i could be going about this all wrong... the black wire may not be negative... but why wouldn't a black wire be negative -logically-  ?  

hmm.. actually, i don't see this grounding anywhere at all upon further inspection.. the green wire seems to be negative where the black seems to be power... and the black n white pulls power from the black wire through the on off on switch and then feeds to the coils which go to the points and condensers..


 please correct me if i'm wrong at this point...


----------


 ok so if that IS the case, and the black wire is +  

then, in theory, if i just ran a new wire in place of the blue wire, this sucker should fire right up right?


-----------nope --------

 i did that the other day with absolutely no luck.... still dead....  


i dunno.. i think it's coming along now but i'd still like more advice...  

i'm going to try switching where the black wires plug into the black and white wires instead of changing the yellow and blue wires, and see if that gives the blue wire power.


 if it does, then i'll just replace part of the b/w wire and i think i'll have power to all 4 cylinders finally and can fire this beast up...

i'll keep you guys posted....