CB200 carb issues

[Johnwebley]

after  much pondering,playing,testing

  Ihave come to the conclusion ,it an ignition issue,

  all my other bikes have  electronic ignition,this  still has damn points,one set and two lobes on the cam,rub at half engine speed.
set the gap at the lower end of the range,massive improvement,

 need  an electrical engineer to explain how the gap/dwell  etc  works with a twin plug coil.

[K2-K6]

Dwell is the overall descriptor for the amount of time the points are closed, which is filling the coils with energy.

The "time" element is what the coils see as it's just the amount of time it takes to replenish that coil at that resistance, with the volts available.

Dwell is expressed in angle/degrees rotation of cam, setting the points gives a specific angle of geometry that the points are closed for.

Now it gets more interesting as when that angle is set, then when revs go up the angle remains the same but with time now shorter the faster you go. Meaning the coils fill less, because they only "see" time connected to supply.

Closing points gap makes dwell too long technically,  but lengthens the time available to fill the coil, at the same rpm.

Good electronic system can just control the time only, and regardless of rpm. So coil saturation is constant from low to high.

If you close the points gap to minimum and set plugs also to absolute minimum spec gap, then it should have the best performing spark output for that system.

[K2-K6]

It can be seen also a different result by use of different coil primary resistance to change characteristics, usually to the detrimental though.

If our systems use 5 Ohms resistance it requires a longer time to fill than a 3 Ohms coil. Putting a 3 Ohms coil into a points system may have advantages at constant high rpm (as the dwell time shortens it can still meet the fill requirements) but at constant low speed the coil is now reaching saturation and then some, causing too much draw and potentially overheating the coil.

So you're stuck with aggregated performance over the rpm range in reality, works OK usually though.

Full electronic in concisely controlling the "dwell" characteristics in fixed time only can make use of whatever their system's designer specifically incorporates.

As example;- a V8 with single coil and firing 4 times a revolution can use a 1.5 Ohms coil with attendant dwell characteristic provided by the electronic switching to help with fill and replenish cycle that are overall shorter to fit in with that firing demand.

[Bryanj]

Works exactly same as a single output coil, on a single output one end of the secondary is grounded the other to the plug, on a twin both ends go to plugs

[Johnwebley]

  thank you gentlemen,

  it is a new coil  listed for the CB200,

  using  25thou   plug gap,

a great improvement  on before,

[Johnwebley]

It can be seen also a different result by use of different coil primary resistance to change characteristics, usually to the detrimental though.

If our systems use 5 Ohms resistance it requires a longer time to fill than a 3 Ohms coil. Putting a 3 Ohms coil into a points system may have advantages at constant high rpm (as the dwell time shortens it can still meet the fill requirements) but at constant low speed the coil is now reaching saturation and then some, causing too much draw and potentially overheating the coil.

So you're stuck with aggregated performance over the rpm range in reality, works OK usually though.

Full electronic in concisely controlling the "dwell" characteristics in fixed time only can make use of whatever their system's designer specifically incorporates.

As example;- a V8 with single coil and firing 4 times a revolution can use a 1.5 Ohms coil with attendant dwell characteristic provided by the electronic switching to help with fill and replenish cycle that are overall shorter to fit in with that firing demand.

 does anyone know the resistance  of the original  coil?

  the one I have is 4.7ohm,

  another is available  at4.2,

  the bike runs well up to  just over 6k.. then cuts out,

  could the points be bouncing?
 these old fashions gubbins  are not easy to sort

[Sesman]

Err, the ohmic value is the resistive, self limiting current characteristic of the coil, which for all intents and purposes permits a steady DC current to flow following a very short time constant . The coil doesn’t ‘charge up’ as such. The HT voltage produced is simply a function of the coil inductance, which creates a back EMF(voltage) as a function of Ldi/dt. In other words the faster the current collapses the bigger the spark as a function of the coil transformation ratio. ‘Relatively’, the primary has a few turns in large cross sectional area conductors, the secondary has lots and lots of turns in very small cross sectional area conductor. It’s called the voltage turns ratio. Deepest apologies to those who already know this….there are lots of you who patently do. The coil will have a time constant, determined by the L/R (inductance to resistance) ratio which means when switched on the current rises exponentially. The current falls in the same way when the current is switched off. An ideal coil would have no resistive characteristic, but we need it on our bikes to limit the coil input current.  Without resistance the coil would appear as a short circuit to the steady state DC current. In truth there is a little ripple in the dc current which will interact to some extent with the coil inductance/ reactance, but this is of trivial effect.

Misfires can sometimes manifest themselves at higher rpm as the HT voltage rises causing arcing across failing insulation. Points bounce is of course also a potential problem.

Did you know our coils also have ‘capacitance’, buts that’s another story……

[Oddjob]

And so says Professor Frink. Jesus Phil, even I didn't understand that, I just test them, if they fire that's good, if they don't well that's not so good, if they shock you, that's bad.

[Laverdaroo]

Kin 'el.  I'm with you Ken!


I'm sure youre right though Phil, sounds it!

[Sesman]

Oh aye, agree with that Ken.

[Sesman]

I thought I was dylysic, but didn’t read anything into it. Apologies but it’s the landlords, hic.

[Laverdaroo]

 

[SteveD CB500K0]

Ldi/dt

Engineering porn.


Sent from my iPhone using Tapatalk

[K2-K6]

Good explanation Sesman, I'm not so versed in electronic theory but try to convert to user view to understand it myself in reference to how a ignition system performs. 

The spark form is of course affected by "atmospherics" within the combustion chamber, in so much as stratified charge density, plug gap and cylinder pressure alter the resistance across the plug gap, and subsequently the duration of the spark when running conditions shift. This area is really interesting but we're not allowed to discuss it on forum by Delta's determination  and limited view of the topic 

[McCabe-Thiele (Ted)]

I thought I was dylysic, but didn’t read anything into it. Apologies but it’s the landlords, hic.

That Timothy Taylor has a lot to answer for.😁😁😁