OzVMX Forum
Marque Remarks => Yamaha => Topic started by: mitch75 on July 20, 2012, 12:10:59 pm
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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.
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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.
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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?
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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?
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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.
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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.
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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.
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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.
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don't know why that post went weird ??? but there ya go
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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.
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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.
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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...............................
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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 ;D
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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.
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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.
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Sorry, one more to my first post. After getting over the 490 sheared key on arrival thing & finding it ran faulty anyway after fixing that [key] just didn't kick back any more--found faulty connections in the multi plug going to the 'box' from the loom so put separate plus on & never looked back, which got me thinking the original stator might still be ok [in usa] so the guy sent it for the cost of freight & [i have a YZ465H in an IT250K frame] it's been running without fault on my other bike for a few years now. Bloody electrics aye!!, sent to try us.
Remember another [just lucky] trick on an old DT125 water cooled trail bike. Bought it locked up & screws had come out of stator coils & lunched it. Salvaged the charge coil & ditched the destroyed pulser coil so [in desperation] hooked up a combine coil/cdi secondary coil off an RG50 or most small JR50 etc, strobed it & was near enough to what i thought was right & never looked back, [ran for years]. Was triggered by [you tell me?] i think the magnets changing [polarity?] going over & exiting--or exciting the charge coil. Was obviously how it is supposed to work on whatever the coil/box came off as was only a black/red tracer single wire coil as i recall or maybe another for earth or just for the kill switch [can't remember now] but basically all done from the charge coil only. Good simple set up, just no advance/retard characteristics i think--but was timed right for running.
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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 ;D
No I said burn period is 50deg NEVER said it varies with RPM.Flame speed will be the same regardless of a weak spark. Burn period is about 50deg.
Honda system was the 'Active Radical' from the CRM250
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I like your give it a go attitude Overthehill.
By what i understand as engine speed increases so does the voltage in coil this rise in voltage is used to advance the timing.
A over voltage pulser would cause to much advance at starting.
Putting a resistor inline would bring down the voltage going to the CDI retarding it making it easy to start.
How does it trigger there are four magnets in there? Sealed box magic?
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I like your give it a go attitude Overthehill.
By what i understand as engine speed increases so does the voltage in coil this rise in voltage is used to advance the timing.
A over voltage pulser would cause to much advance at starting.
Putting a resistor inline would bring down the voltage going to the CDI retarding it making it easy to start.
How does it trigger there are four magnets in there? Sealed box magic?
I've give up on the fuel burn vs deg thing ::)
The voltage in the coil would only rise to a certain point when the iron circuit and coil become saturated the actual voltage of the pulsar coil is less important than its timing. The pulsar coil triggers the ignition on its leading edge usually as the voltage rises once trigger voltage has been reached the voltage peak does not matter. The amount of advance gained by the increased voltage would be so small as not to matter and is not taken into account (we are talking <1deg and is much less than the accuracy the analog system is capable of) although if you had a double would pulsar coil then a step change in advance would be used. Now if the voltage was reduced (shorted turns) then timing may vary particularly at kick speed and the plug may miss some fire strokes meaning that there is unburnt fuel already in the engine on the next fire stroke? Could this cause backfires?
There are four magnets in the flywheel and you will find one has a much stronger magnetic strength than the others, you may or may not feel the difference without a gauss meter. The extra strength of one magnet may also be achieved by having a concentrator iron circuit over one magnet or one magnet larger than the others and only that magnet passes very close to the pulsar coil. This extra magnetic strength makes no difference to the charge coils but means that the pulse coil gives four pulses but one pulse is much larger than the others and this pulse is large enough to trigger the ignition. There is a lot of EMF stuff going on inside the flywheeland stator an old analog electronic ignition system. Much of the stuff is not relevant to the ignition system and is filtered out or more accurately ignored by the ignition system. Newer digital system are actually much simpler in there operation as the trigger system is simple and very accurate.
I still can not see how the added resistor could improve things ???
Having said all that they are very simple systems and wil survive some major damage and still function. It is only when pressed to the limit such as racing that they show their true performance or otherwise.
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Thanks again Montynut.
So it's a fail on the resistor oh well worth a try and with the pulser being N/A any fix would be good.
Maybe it has shown up a bad connection.
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Thanks again Montynut.
So it's a fail on the resistor oh well worth a try and with the pulser being N/A any fix would be good.
Maybe it has shown up a bad connection.
A bad connect is possible but low resistance measurement does not support that. A high resistance would indicate a poor connection.
Small Coil Rewinds in VIC or Betta bikes in Adelaide will easily rewind the stator coils for you. If you have one coil rewound get the lot done as they are now 30+ yrs old
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My give it a go attitude is more based on the old "fix it but doonn't spend any money" trick haha. Suppose the non trigger coil system i 'jacked up' on the kids dt125 was similar to my lawnmower or chainsaw [or KT100 gokart for that matter] with just coil & box combined. Love reading the heavy stuff that 'montynut' puts up here, bit beyond me but trying to follow it, [i'm from the points ignition days]. In saying that my old [now farm] Mazda 626 coupe fried the distributor module 10 years ago so i put an external unit on i had off a toyota grande & found the trigger wire in the module [wire was visible out the side of module but under the 'des' cap, wire came out then went back in further around] gave a couple of peak volts at wind over so wired it to the external box, unhooked the vacuum advance as thought the trigger wire wouldn't like being constantly flexed & gave it a bit more static advance by moving distributor. Still used every day down the farm. Sorry, getting off subject. Lots of [desperation tricks] down here in the land of the "long wet cloud". Thanks.
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Me again. Semi-serious question for 'Montynut', i have a yamy yzf750sp that is blubbery just off idle which sounds like it's not uncommon with these [flat slide FCR 39mm carbs] when the slide needles & needle jets become worn, needles look ok actually [going to leaning them off a notch to try], but i'll swear it's worse since taking the resistors out of the plug caps [might be my imagination!!]. Resisters were faulty in two with almost off the scale resistance & two had 10k, maybe they're 10k caps but would have thought 5k [don't know]. Two that had super high resistance out of the caps were open circuit when in due to corrosion on the long springs that hold them in [tall caps these]. Replaced with a 4 or 5mm rod in each which at least gave good connection right through but i think [am i wrong?] the rich carburetion as you move off above idle seems worse. Might be mind over matter, but can a system designed for resistor caps suffer in a way such as holding onto retard a bit longer due to lack of resistance, so i have to give it a bit more throttle to get past that which aggravates the rich symptom. Hope you can follow all my ramblings 'Montynut'--or anyone else out there. Also do you think 10k caps could be normal? or think 5k. Been chasing easily fouled plugs on two but caps problem seems like it was the cause as ok now with same plugs. [fingers crossed]. Thanks.
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Checkout NGK website for resistor caps.
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5K is normal I assume you don't have resistor plug. If you have removed the resistors in the plug cap then install suitable resistor plugs.
If the system was designed for a resistor in the HT side of the system then it needs to be there otherwise the system will misbehave causing poor performance including erratic running and massive RF noise it can also damage the system. It effectively overloads the HT system.
Analog PVL systems recommend no resistor in the HT circuit but their digital systems require a resistor otherwise they will misbehave and will be damaged.
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Montynut. Have you worked on a DT 360a ignition?.
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No - I'm afraid not
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talking about my 750 from last night, i forgot i had a cd of the haynes service manual [never played it]. Says 10k for caps so that's a surprise & plugs are NGK-CR9 something--i have the ND equivalent plugs by memory [will check]. assuming the 'R' in CR9 stands for resistor & if it's say a 5k resistance plug then the system must like having 15k resistance in original form? [maybe R plugs are 10k? don't know], plus up to 0.9--36 thou gap [.8 to .9] must be a good system from new. Going to check the valve clearance in case they've closed up to 'minus zero' before putting carbs back on [again]. Hate doing shim clearances, give me my old B33 or Matchy from the 60's with a couple of easy to get at pushrods.
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Off topic, but the amount of excellent information being provided here, and the amount of time some put in to help others, is the reason why those who start threads, gather the info they need and then delete the whole lot to cover their tracks, should hang their heads in shame.
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Has anyone opened up a old Yamaha CDI?
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I haven't opened one up but i've been trying to seal one up that was leaking black ooze with some Sikaflex. Didn't work.
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Thank you for your excellent information on what not to use to seal a CDI mainline.
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No worries, i'll let you know how the Nugget shoe polish holds up
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Actually, a mate of mine who's into electronics mentioned araldite? Might be worth a try.
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5min Arildite is fine but be careful of mixing and potting a large quantity in one go as it generates a large amount of heat and expands slightly.
casting resin is good but use minimum hardener so that internal heating is kept down.
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Is the DT 360a a stepped type pulser?.
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I think this is how the spark advance system works on these bikes.
High tech stuff for the seventies.
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most 2st of the '70 and even '80s had static timing with maybe one step change at low rpm
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Do you read silicon chip magazine Montynut.
The May 2008. Issue has a section on building CDI module.
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I like your give it a go attitude Overthehill.
By what i understand as engine speed increases so does the voltage in coil this rise in voltage is used to advance the timing.
A over voltage pulser would cause to much advance at starting.
Putting a resistor inline would bring down the voltage going to the CDI retarding it making it easy to start.
How does it trigger there are four magnets in there? Sealed box magic?
According to my suzuki book mitch75 that's exactly how they get the setup to advance.
The scr triggers at a set voltage and the system reaches the trigger voltage earlier as the revs rise.
Seeing as how two strokes don't need any advance the only reason I can see for the advance setup is easier starting , less kickback.
I have a DT 175 flywheel here [ 4 magnets and 2 bigger gaps ] and it fires twice per rev , 1 TDC and 1 BDC.
Not a problem firing at BDC as nothing happens.
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They use the AC wave form and get it to trigger at low voltage 1.5v.
As speed increases so does the wave form reaching the 1.5v quicker.
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your right about firing twice per revolution, accidentally found that when strobing by old AG100 [cdi ignition], had me head scratching for a while but thought in the end--nothing to stop it doing that!!. Had an MX250b new in"75 'with the two step' trigger [retard & advance]--same type set up as the DT360A except for the full flywheel. Anyway the MX went strong right out of the box then next year"76 YZ250C mine was a slug compared to year before. Took me frustrating ages to find an answer as mechanically identical motor. But found the ignition was [too trick for me] so strobed it & found it advanced to [i dunno] lots, say 36 degrees then retarded off gradually to bloody near tdc at full revs so though bugger it & just over-advanced it on the backplate which fixed it, didn't ever give any problems. BUT--asked the Yam factory mechanics that came to our work with the importer [they were doing the rounds & we were to line up a few problem jobs--was fun watching their methodology for working it. They were on to anything we could throw at them--damn. Anyway, asked them [why] re-ignition & they said we do that to stop you blowing it up by over-revving. Bugger that i thought [in those days] give me power. Cheers.