2&3 Cylinders not firing PLEASE HELP! CB750K3

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2&3 Cylinders not firing PLEASE HELP! CB750K3

Luccondon
Hey All,

I have recently bought my first bike, a 1973 CB750K with 11,000 miles on it.  The stock pipes have been taken off and replaced with a 4 into 2 system.  When I picked it up, it had some backfiring caused by a worn out spark plug wire on the 3rd cylinder and there had not been any maintenance on the bike for 2 years.  I immediately had the carbs cleaned and synched, new spark plugs installed, changed the oil, re-set the ignition points, adjusted the tappets and also the camchain.  It ran better but was still backfiring due to the frayed spark plug cable, so I changed out the right side coil for the 2/3 cylinders along with putting on new NGK resistor caps.  Since doing that, I have lost both of them and they will not fire up.  When I start up the bike it idles perfectly at just over 1,000 rpm but the middle two headers are stone cold.  

HELP!!  This is my first bike and I have tried picking up everything that I can from these hallowed forums, but I don't want to drop more money on a mechanic for them to just dig around.

Thanks, Lucas
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Re: 2&3 Cylinders not firing PLEASE HELP! CB750K3

TOOLS1
Administrator
A GOOD mechanic would have that bike running in about 30 min. First check to see if you are getting power to that coil. Check at the black wire that connects to both coils. If you have power at the black wire, check the points for that coil. It should be the set on the right that the yellow wire from that coil runs to.
TOOLS
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1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: 2&3 Cylinders not firing PLEASE HELP! CB750K3

Luccondon
Thanks, TOOLS

I reattached all of the wiring coming from the harness last night and found a frayed bullet connector at the base of the feed for the new coil.  Bought a new one and it fired right up!

Thanks All