weak spark

Hi all.
I have another electrical woe that i hope someone may be able to help with. All previous issues with loss of electric are now ok but the bike broke down with a total loss of spark, the unit was returned to Boyer Bransden who said it had failed completely so i bought a new one and 2 new coils  but now the spark is very weak and the engine will not start.
Could the coils be wired incorrectly or if anyone has any advice where to look i would be very grateful.
I have new B7ES plugs and the bike has the red NGK plug caps.
Thanks
Andy

What voltage do you have at the coils. If below battery voltage might be prudent to do the wiredgeorge relay mod.
 

It usually helps to mention exactly what motorcycle it is & what system you got. The Boyer Bransden site has a fault finding page. I would make sure the battery is good.

The by-pass relay is a good shout if the voltage is low at the coils ( a lot quicker and cheaper than tracking down lot's of small losses which add up to a big one) if the voltage is ok something else that might be worth checking (I don't know if it is relevant to your set-up)
Many years ago I had a "BB" ignition on a KH400 that I bought cheap as a non-runner because it had no spark, the trigger wiring to the switched side of all three coils had diodes installed to stop the trigger back feeding the coils. All three diodes where blown so $3 later with three new diodes started first kick 
PS: did you get the new coils from "BB" ? Looking at the add on "Z Power" they seem to recommend lower resistance coils with their latest units, what resistance coils did you fit ?

Very good point re the coil modincluded is a pdf of that mod i did to the Z500 was loosing quite a bit of voltage thanks to the std thin wires. 

wrote:

Very good point re the coil modincluded is a pdf of that mod i did to the Z500 was loosing quite a bit of voltage thanks to the std thin wires. 

File Attachment:

File Name: Z500 coil ....zip.zip
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Thin wires don't help but age is the key problem. The coil feed on most of these bikes runs through several components and connectors. Over time as corrosion takes hold you get resistance. If you loose 0.2v (which is no big deal) at each of the  seven or eight junctions you are now loosing 1.4v which is a big deal. These issues sneak up on you over time
 

hi
there is 12.7 volts

sorry, yes i forgot, it is a 1978 US import z650 B2

hi
im not sure about the coils they are after market ones off the internet, it has the same problem with the original kawasaki coils

Does your meter have a resistance setting?  Alternatively, wherever you got the coils might list the resistance. The stock 650B coils would be around 4.0 ohm for points ignition.

4 ohms at 12.7 volts will draw 3.175 amps ( 40 Watts) whereas at 14.5 volts it will draw 3.6 amps ( 52 Watts) so you get more energy to saturate the primary coil, so more energy in the spark when the points open.

Place you volt meter in DC volts one probe on the + bat terminal and the other on the coil wire (Red-Yellow??) not he neg coil wire (black-wire??) and turn the ign on with kill button on run and see what voltage is dropped with the coils powered any more that 1.4 you prob get a weak spark. you can do this engine running too (prob better)

 

So it looks like the supply voltage is all good (unless it drops like a stone when cranking the engine) You can connect the voltmeter red lead to battery positive and black lead to coil feed wire then crank the engine, you are looking for no more than 0.5v as you are measuring the difference between the coil and the battery.
I would suggest dropping "BB" an email for guidance on which coils to use with your new ignition module (the add on the "Z power" website lists a full kit with coils or just the module) the full kit uses lower resistance coils than standard due to the pulse duration being shorter than standard to get the best spark