Topic: '80 CB650 weak spark

[hoofinit]

Hello all,
   This is the first time posting on this forum, so a little patience will be greatly appreciated.  I have a 1980 CB650 which until this spring, ran great... now only takes 15 minutes to foul a set of plugs.  The bike is now charging good after replacing the stator.  If I take the plug out (on any cylinder) and ground it, even a new plug barely has spark.  The battery is new and fully charged.  I'm suspecting the spark units, you guys have any ideas?

[Pinhead]

You could be dropping voltage between the battery and the coils. With the key on, engine not running, measure the voltage between the positive terminal of the battery and the positive terminal of each coil. There's usually a pretty appreciable drop since the power has to go through the main fuse, key switch, kill switch, and then to the coils.

If this is your problem, it can be eliminated with a single relay and a few feet of wire. You'll basically be using the current "hot" wire that feeds the coils to engage the relay. A wire straight from the battery terminal will go through the contacts of the relay and now feed the power to the coils (through a fuse, of course).

My bike was dropping over a volt at idle and a volt-and-a-half above 2000 rpm before. Now with the relay installed, there is no measurable voltage drop and idle is much smoother, plugs last much longer (current set is over 2 years old) and my gas mileage has improved.

[prosolar]

It kinda sounds like your problem might be the carbs letting in too much fuel. The spark on any old bike always seems a little weak and can't compensate for much in the way of rich running which is why a lot of people run Dyna coils and ignition. I don't disagree with pinhead but I think you should look at your mixture.