Topic: Modern Coils for a CB500K, Spark plug voltage with stock coils

[Lorbaez]

Just one simple question:

is it possible to use a pair of coils from a CDI system in a CB500K?

I measured 3.5 ohms in primary coil. Is it OK? I read that 3ohms coils works OK but reduces point's live.

The ones I have belongs to an old Honda RC30. Honda reference 30510-MR7-003.

[Lorbaez]

Just one simple question:

is it possible to use a pair of coils from a CDI system in a CB500K?

I measured 3.5 ohms in primary coil. Is it OK? I read that 3ohms coils works OK but reduces point's live.

The ones I have belongs to an old Honda RC30. Honda reference 30510-MR7-003.

Just four your reference Coil are TEC and code is MP08

[Lorbaez]

Just one simple question:

is it possible to use a pair of coils from a CDI system in a CB500K?

I measured 3.5 ohms in primary coil. Is it OK? I read that 3ohms coils works OK but reduces point's live.

The ones I have belongs to an old Honda RC30. Honda reference 30510-MR7-003.

Just four your reference Coil are TEC and code is MP08

My bike has stock breaker system.

[Lorbaez]

I want to replace them because I notice a big difference on spark voltage comparing each cylinder.
In fact my bike does not mantain idle speed, choke must be open at least 10% to start the engine even when itis hot. Exhaust are cold compared to the engine.

[dave500]

coils from a cdi type ignition are not suitable no matter what the ohms,,they have a different charge rate,just find some replacement type 5 ohms to suit,david silvers can supply these,also check the spark plug cap resistance.
http://www.davidsilverspares.co.uk/CB500K2-FOUR-1973-USA/part_83527/

[TwoTired]

I expect what Dave posted is true.  I would need to know both the primary resistance and the secondary resistance to have a clue about cross function.

CDIs usually provide ~300 volts to the primary with a very short pulse, while the stock system stores a charge in the coils themselves with a 12 V input during dwell time.

Stock coils have a secondary resistance in the neighborhood of 15KΩ.  If the coils you have measure in this proximity, they might work at the expense of shorter point life.  I suspect, however, that if they are optimized for a CDI's 300 volt input pulse, the secondary turns count is substantially lower and will have a lower resistance.

Cheers,

[bwaller]

I can offer a response from the very practical side and agree with Dave & TT.  I tried a set in my race bike, thinking these pulse type coils might be worth a try in the small reworked CB500 chamber. It would rev cleanly to 9300 then hit the wall as if it was a carburation problem. They will wear your points prematurely, best to look at "plan B".

[CB500_k2]

It may be a small point but 3 ohm coils pull more current than the stock 5ohms.  With the charging system on the 500 a bit on the under-sized, this can be an issue.  It was for me and I switched the 3 ohm after market coils out for Dyna 5 ohm coils.  Bike has worked great since.

[bwaller]

It may be a small point but 3 ohm coils pull more current than the stock 5ohms.  With the charging system on the 500 a bit on the under-sized, this can be an issue.  It was for me and I switched the 3 ohm after market coils out for Dyna 5 ohm coils.  Bike has worked great since.

That or install Hondamans coil resisitor kit on your 3ohm.

[Lorbaez]

Thank to all your for your quick reply. Finally what I Asumed is a problem it is normal. I found an old ignition tool manual that say secondary voltage for cb500 is 15kv for cyl. 1 &3 and 8kv for other 2. Just what my coils suply.
My problem was caused by improper advance adjustment.
one more question. Do you disconect condensers during timing adjustment?
To make it easier I connect my lamp directly to battery positive pole and negative to the point. If condenser are connected lamp is on during 360º, just intensity decrease when point is open. The only way to see the lamp off is disconnecting condensers.

[TwoTired]

I found an old ignition tool manual that say secondary voltage for cb500 is 15kv for cyl. 1 &3 and 8kv for other 2. Just what my coils suply.

I'm sure this is not correct.  The is no reasonable explanation why spark plugs would require different voltages among cylinders.  Further, one coil feeds spark to 2&3 and the other feeds 1&4 and they are identical except for lead length.

Do you disconect condensers during timing adjustment?

No.

To make it easier I connect my lamp directly to battery positive pole and negative to the point. If condenser are connected lamp is on during 360º, just intensity decrease when point is open. The only way to see the lamp off is disconnecting condensers.

The Test light is connected across the open point contact for on, and goes off when the point contacts are closed.  The condenser doesn't matter if it is functioning properly.

[Lorbaez]

[

I found an old ignition tool manual that say secondary voltage for cb500 is 15kv for cyl. 1 &3 and 8kv for other 2. Just what my coils suply.

I'm sure this is not correct.  The is no reasonable explanation why spark plugs would require different voltages among cylinders.  Further, one coil feeds spark to 2&3 and the other feeds 1&4 and they are identical except for lead length.
[/quote]

I agree with you but please see attached picture from an operating manual of an old electronic ignition tester. It is related to CB750K with CDI but spark plug voltage is 8kV por 1&3 and 13kV por 2&4. these are the values I measured on my bike

[Lorbaez]

There is no sense also for me but this is the evidence

[TwoTired]

What instrument did you use to measure 13,000 volts?

I see that the voltage differences per cylinder are an artifact of the wasted spark scheme.

FYI, that document describes a TCI system, not a CDI system.

CDI - Capacitor discharge ignition.
TCI - Transistor controlled ignition.

[Lorbaez]

What instrument did you use to measure 13,000 volts?

You are right TwoTired, It sis a TCI system.
I use Ignitionmate to check high voltage. http://www.tecmate.com/d_ignition.php.

Does somebody have an ignition tool to check spark voltage? could be interesting to reconfirm these data.

[TwoTired]

I hadn't heard of or seen an ignitionmate.  But, it looks damn handy.  They do cost $450 and up to buy though.  Do you own one or borrow one?

IgnitionMate Peak voltage tester

As a time wasting project, I'm trying to make an HV probe for my oscilloscope. 
 But, I'm more interested in waveform timing data than actual voltage measurement peaks.  The voltage used at the plugs is determined by the spark gap and the atmosphere within the gap.  All operating ignition coils have a reserve capacity/capability above what is actually used at the plugs.

Cheers,

[Lorbaez]

I hadn't heard of or seen an ignitionmate.  But, it looks damn handy.  They do cost $450 and up to buy though.  Do you own one or borrow one?

I own it, it is very easy to use.