DT 360 A. Pulser coil fix.

[mitch75]

Been having kick back when starting bike.
Did a resitance test on pulser coil was out. (CDI).
Chucked a resitor in line bring back to spec seem to be better now.

[pancho]

 Interesting.
 My theory on kick-back is that a weak spark on starting, especially more so when the engine is cold occurs because the flame travel is so slow as a result of the weak spark that the pressure rise reaches a high point when the piston is on the next compression stroke.
  Logical I suppose.
pancho.

[Lozza]

Flame speed will be the same regardless of a weak spark. Burn period is about 50deg.

Mitch that's a very elegant solution can you go tell us the specs?

[Montynut]

How does putting a resistor in series with a coil that is down on its continuity (ohm)  reading fix anything? The low ohm reading across a coil indicates that some of the coil turns are most likely shorted out. This means that the coil output will be reduced because the output is directly related to the number of functional turns on a coil exposed to a moving magnetic flux. Adding a resistor will actually increase the load on the coil and will reduce its effective output to the CDI unit even further.

The function of a coil has nothing to do with its resistance its operation relates to it's inductance measured in 'henry'. The coil resistance just tells you if the coil is complete. A low resistance value tells you it has shorted or low turns and high resistance tells you it has excess turns, is damaged or open circuit.

If you do have a pulsar coil with shorted turns this could lead to inaccurate timing as the coil output could possibly be inconsistent. That again goes against your finding of putting a resistor in series improved the situation. Maybe the resistor retarded the ignition?

[mitch75]

Thanks for the explanation Montynut.
When i did the resistance check it was 75 ohm should be 90 ohm +- 9% put a 10 ohm resistor inline between the plugs using some bullet plugs.
I was thinking of the whole circuit not just the coil.

[OverTheHill]

without reading all posts sorry i'll just tell a story of my old dt360a  i used to ride to work. They have a two stage pulser by memory--a green/white plus red/white & starts on one half [no kick back as is retard position] then at around 1500rpm [guessing] it flicks to the advance half & stays there [as in no variation through revs] till a very slow idle & starting kick revolutions]. First thought if kicking back is "Has it sheared off the flywheel key & moved a bit--do mine up real tight with a half inch breaker bar socket & a rigid holding tool in flywheel slots then let it rest on footrest while tightening & Be careful of coils with holding tool. ummm--anyway long story [long] mine stuffed the [half] the pulser & wouldn't start. Was just the retard bit but has to get through that to get to advanced stage so i grounded that half [say green/white probably but might be the other] & never missed a beat after that "BUT" because it was starting on advance you had to be sure to give her a good solid kick starting from the top or [like an older RT2/3-360 she'd let you know about it with a good kick back. In you case though & if it's a kick back on a DT360A & it's not my old one [newzealand] i'd be looking at the old [sheared a key' trick. Sorry about the spelling & the long story plus if i got the your story wrong--have to read it all. Cheers.

[Montynut]

Thanks for the explanation Montynut.
When i did the resistance check it was 75 ohm should be 90 ohm +- 9% put a 10 ohm resistor inline between the plugs using some bullet plugs.
I was thinking of the whole circuit not just the coil.

OverTheHill makes some very good points regarding the timing being out.

What I am saying is the actual resistance of the coil circuit is not relevant to the operation of the ignition system it just allows you to take a measurment that will tell you if the coil is complete and within a value that indicates the correct number of turns on the coil. Measuring reluctance is difficult and it varies with frequency and in a voltage generating sense (as in a pulsar oil) does not tell you very much as the iron cicuit and strength of the magnets all have an effect

If the coil resistance is low just adding a simple resistor will not do anything to the circuit to bring it back to its designed performance. In fact it will have the opposite effect of adding load to the coil once it is in operation.

[pancho]

Flame speed will be the same regardless of a weak spark. Burn period is about 50deg.

Wouldn't you say that the burn speed is over a period of time, the degrees of rotation therefore depending on RPM?
From my experience I would still think that a poor spark does indeed lead to a poor flame propagation delivering slower burning.
I am interested in more thoughts on this, especially what is actually happening when a kick-back occurs on starting and more so on a cold engine when engines will generally tolerate MORE advance, and why the problem seems to happen less with a more intense spark at kick-over speed as when a simple Kettering system (coil, condenser, battery) is utilised.
cheers pancho.

[pancho]

 don't know why that post went weird  but there ya go

[Lozza]

You enclosed everything within the

and [(forward slash)quote]  type.

Spark intensity is usualy lower at higher RPM due to the coil not being fully charged. Poor flame propagation is more to do with head design and the power(amps) of the ignition.  From flame kernel to end burn period will be 50deg regardless of rpm.

[Montynut]

You enclosed everything within the

and [(forward slash)quote]  type.

Spark intensity is usualy lower at higher RPM due to the coil not being fully charged. Poor flame propagation is more to do with head design and the power(amps) of the ignition.  From flame kernel to end burn period will be 50deg regardless of rpm.

That does not make sense a fuel air mixture when supplied in the correct ratio burns at a constant rate, although different fuels burn at different rates naturally. That applies in any combustion engine internal or external type even in firearms the burn rate is constant. Otherwise why have an advance curve if the burn was always 50deg static timing would be the way to go regardless of rpm.

Spark intensity is constant in a kettering system probably even best at tick over. What do you mean by a coil charged up? I assume you mean the charge on the capacitor in a CDI system.

[Lozza]

We are not talking about kettering systems (whatever they are) we're talking about CDI's. Yeah I meant the cap.Really trick GP ignitions use variable voltage with RPM.

Timing is another question all together, the first of 50 reasons why we don't have 50deg static timing is the exhaust port would still be open............................... 

[Montynut]

No one mentioned 50deg static timimg. The 50deg comes from your thoery on combustion time varying with rpm which does not seem to be logical. Combustion is simply a conversion of a hydrocarbon fuel to heat and gases considered to be waste. This is a chemical process which takes place at virtually a constant rate.

A kettering system is a basic old total loss points system. The battery may be charged by a seperate charging system but the ignition powers supply is independent to the engine rotation.

Last post

[OverTheHill]

My understanding of cdi/tci ignition is pretty basic but usually solve it in the end. [have a peak volt meter which helps when ohms reading is doubtful--But, got a stator plate for my yz490k off ebay some time ago & kicked back so hard it had me re-checking flywheel key etc but turned out to be a crook pulser making much more than the couple of volts at kick start speed. Bought the plate to get a good charge [source coil] as old one had given up, as they do, & really caused some headaches. Swapped original pulser & still ok a year later. Bought the 490 from ebay many years ago & guy had swapped stator just prior to advertising for sale & hadn't tightened flywheel. First kick here on arrival [excitement] bastard kicked back so hard it broke a tooth off idler gear & bent teeth on kick gear. Turned out he'd started it & switched off & must have sheared key during that unknown to him. Despite that he was a really good helpful guy to buy from so far as crating up to send etc. Thanks. ps, strobed it [kick it harder dear!!] to see where was firing [plug out of course--should have left it in & said to wifey--what are you doing--kick it!!]. Anyway i digress, was firing 90 degrees out--[that was the crook pulser problem one]. I'll start another post with a new question for you electronic whizzes.

[OverTheHill]

Here's a question. Honda made a 250 '2stroke' trail bike i think back in the "90's, think it was in production but never saw one where by the ignition when not under load [i think] was done by compression ignition [no, not a diesel]. As i recall it had a power valve [type thing] that fully closed exhaust port & shut off the spark, or closed the exhaust port for a period of the stroke to aid compression pressure then opened it after it compression ignited to exhaust it. Anyone heard of it?, & was it flagged in the end as too complicated etc or too far out of the ordinary to sell. Think it was done for economy & pollution reasons. Thanks.