Topic: Calling electrical guru's: harley coils might be causing problems

[davis96]

Hey guys I need your help, can't seem to find the right search terms to yield a good answer:

so in my last rebuild of my bike ('74 cb350f) i went with two generic 12v harley coils which actually work to make the bike run. I am running a small 12v scooter battery with no starter. 

you can see the coils in this picture:


- the problem is that after riding for a bit the battery will act like it is dead and the bike will die.
- the wierd thing is that after you let the bike sit with the ignition off for a bit, you can actually watch the volts go from like 8 volts and steadily climb all the way back to more than 12 volts and it will start back up. 

- I'm thinking maybe these coils draw a little bit more than the stock ones and store the charge, acting as a capacitor; then the charge goes back into the battery.

- do any of you electrical whizzes think this could be the problem, and the little battery i have in there is no longer enough to keep the bike running for a long time?

[swellguy]

I think your battery is too small and your coils are too big.

[dave500]

is it charging ok?are they 3 or 5 ohm?

[Skunk Stripe]

How hot is your battery getting? It looks like you may have moved it from its normal location and if it is getting really hot, heat can increase internal resistance I think and when things cool down, it goes back to normal.

[mlinder]

Multimeter:

Red goes on positive of the battery, black on negative.

Start bike. Rev to 5 grand.

What does multimeter say?

CB350's will not charge jack-crap below 4 or 5 grand. They relied on a good battery for any kind of around town riding. How are you riding?

[davis96]

Ok, the coils are 5 ohm like stock, and i only do around town riding to campus and back, with a fair amount of stop and go traffic and lights/stop signs.. This is what I was thinking was the problem, the only time it really screws up is during rush hour traffic. The battery worked fine with stock coils.

[mlinder]

Red goes on positive of the battery, black on negative.

Start bike. Rev to 5 grand.

What does multimeter say?

[Gaither]

Why not try the stock coils again if it ran good with 'em?

Maybe you "fixed something that wasn't broke"?

[dave500]

im going for the crappy scooter battery used in stop go traffic and the three fifties feeble charging combination.

[davis96]

Why not try the stock coils again if it ran good with 'em?

Maybe you "fixed something that wasn't broke"?

well I attempted and failed to add the cloth covered wires to the stock coils, so the stockers are broken.

[davis96]

Red goes on positive of the battery, black on negative.

Start bike. Rev to 5 grand.

What does multimeter say?

well i dont have a tach, installed, but I'll do some testing and let you know what i find

[camelman]

Wow, it looks like you went through more of a bike transformation. Do you still have those old coils?  I would like to get another set to swap in good wires on

Camelman

[fletcha221]

This guy.......

[bollingball]

Post data spec off of battery.And get a longer brake cable

[Bodi]

The 350/400 alternator is weak. It doesn't make as much power as the bike uses below 3000 rpm or so. The battery makes up the difference at low engine speeds. If you have a small battery it won't do so for long. A discharged battery when the load is removed will recover its voltage but still have very little capacity: it will run the bike for a short time even just after having "died".
You can improve the situation by making sure the alternator is at full efficiency, good connections in all the field and stator coil wires, good rectifier, and good regulator. Reduce the lighting power load - use a lower power headlight bulb plus LED running lights and brake/tail light.
You may still need a larger battery for city driving, on the highway you should be charging the battery though.