AC to DC CDI swap, GY6 clone

[lithiumlord]

Well, apparently my recent problems with ZRX kicked in because of the exhaust valve getting overtightened by itself. Ok, got it reset to 0.1mm - some clicking but it's better then a burned valve later on - and... another stall A quick inspection proved the CDI feed coil was open-circuit dead (probably it's faulty condition caused the first stall as well btw, yet who knows and cares).

I guess I'm selling this one for good, better to get a used Silverwing or Skywave - yet I have to get it running anyway. Yet - I want to do it fast, easy and with no s-tools. So the best bet is to get rid of the whole AC CDI concept for good and move on to DC so it's only the circuitry to mess with (and a lower minimum idle RPM btw, nice). I had three different ideas: adding an AC transformer to feed an AC CDI off one of the remaining stock AC generator coils (guess it's also a hell with phasing the charge cycle, also afaik the CDI shorts out the negative halfcycle so a diode would be needed - a useless difficulty anyway). The second way is to add a boost convertor to feed the AC CDI off the DC circuit (cheap yet can get pretty messy as it's a whole 20w or so). For this one I need the exact nominal voltage for the CDI input. And the best one is to just rig a DC CDI.
The question is - are there any DC CDIs that can replace a stock 157QMJ AC one with no engine performance loss (with the old flywheel still there, of course), and can I leave my old ignition coil with those? And, if no, what voltage and current should I design a boost convertor to hold for the stock CDI to become a DC one?

[EPAhater]

The whole concept is easy but why? All you would have to do is buy a Dc one make sure you keep the pulse or trigger wire to the correct spot on the CDI and then run a 12Vdc wire from the key switch to the Dc CDI.

But if you ever mess up and have a dead battery you are a no start scooter, even with the kick starter because of no 12 volts.

Also if you want to convert the AC to DC from the AC coil on the stator I'm not sure the voltage would be steady enoough while cranking to give enough Dc voltage to the CDI for it to even fire and I'm not sure you have enough amps on that simgle AC wire from the stator to do it either when converting it? That AC feed is just from one coil on the stator.

The AC set up works fine as it is especailly in situations where you have a battery or regulator failure because with the kick starter you can start the scooter with a completely dead battery, go to DC and that concept is gone even if you jump start if off of a good battery.

There are no advantages to a DC type CDI whatsoever IMO.

[lithiumlord]

Well, guess I found the model I was looking for in a local store, now to buy and test The dead battery issue is no issue in fact, because:
- we don't need that much power to feed the CDI, usually should you jumpstart the engine the charging current will be more then enough.
- regulator failure is not a very common thing, the AC CDI coil is, however. Even more, swapping both the reg and CDI means a minute of work, swapping a gen coil is long and needs many tools. Therefore should your generator magneto coil die (doubt it will do so in a garage or something) you are stuck bad unless you've got your trusty bag of tools around. All the DC CDI failures can be fixed with a couple of wrenches at most (one for IC, other for sparkplug).
- I removed the kickstarter anyway as it is not the best idea to keep starting a 150ccm engine with it all the time anyway, it's just not built to last.

The only trouble so far is to get the alarm rigged back, though will first mount the thing to a random positive wire and move to garage for a closer look, iirc it connects the light 12v bus as well so it's not a big deal.

[Blueboy5000]

Your valves should be set to .004 and. 005.

I also do not understand how a DC CDI is going to help you. Most bikes (except Kymco) us AC fired CDIs. All stators make AC current. Why would a DC CDI help in any way? Especially since it would need to use rectified DC current created by the VRR.

[Blueboy5000]

There is no statistic stating a DC CDI is less prone to failure than an AC CDI. CDI do not fail regularly, but instead usually fail because of wiring issues, such as a bad ground.

[EPAhater]

Jul 15, 2012 4:23:26 GMT -5 lithiumlord said:

Well, guess I found the model I was looking for in a local store, now to buy and test The dead battery issue is no issue in fact, because:
- we don't need that much power to feed the CDI, usually should you jumpstart the engine the charging current will be more then enough.
- regulator failure is not a very common thing, the AC CDI coil is, however. Even more, swapping both the reg and CDI means a minute of work, swapping a gen coil is long and needs many tools. Therefore should your generator magneto coil die (doubt it will do so in a garage or something) you are stuck bad unless you've got your trusty bag of tools around. All the DC CDI failures can be fixed with a couple of wrenches at most (one for IC, other for sparkplug).
- I removed the kickstarter anyway as it is not the best idea to keep starting a 150ccm engine with it all the time anyway, it's just not built to last.

The only trouble so far is to get the alarm rigged back, though will first mount the thing to a random positive wire and move to garage for a closer look, iirc it connects the light 12v bus as well so it's not a big deal.

regulator failure is not a very common thing

You obviously haven't messed with many scooters, regulator failure is the single mose common failing part on a scooter electrically.

the AC CDI coil is, however.

same thing, I've seen many stators fail on the charging side yet the single AC coil on the stator still function so the scooter will run, in fact rode a scooter around town for nearly a year with no working charging system, just kick started it every day, kept the battery charged for brake lights and turn signals.

I removed the kickstarter anyway as it is not the best idea to keep starting a 150ccm engine with it all the time anyway, it's just not built to last.

Have three kick start type scooters both 4 years old, kickstarter works like a charm, knowing how to use it is the key.

Therefore should your generator magneto coil die (doubt it will do so in a garage or something) you are stuck bad unless you've got your trusty bag of tools around. All the DC CDI failures can be fixed with a couple of wrenches at most (one for IC, other for sparkplug).


You obviously have never been stranded with a dead battery and wished you had a AC system and a kickstarter, guess you can carry a pair of jumper cables with you and hope someone is kind enough to give you a jump? Also if the AC coil fails it doesn't matter what CDI you use you need more than a couple of trusty wrenches to replace it. If you're stranded because of a AC coil failure it doesn't matter which type of CDI you have.

I own 5 scooters from 5 years old and under, 2 DC type CDI's and 3 AC type, never had a CDI or AC coil failure, over 21k in total miles.

BTW the pulse sensor or pick up coil that sends a signal to the CDI it's AC too. They also fail, no way around that one.

Also as I said you can change and go to a Dc type CDI with just one wire run, converting, AC to DC then changing, just adding another part to fail, waste of time and money IMO.

[lithiumlord]

Well, had a sensor failure once (contact welding gone loose) - wasn't that hard to reach the desired spot. As for a dead reg or anything, at most you can bet on a battery fully charged as (a least as far as I know) a DC CDI needs only 12v and around 20w of power, pretty achievable. As for the reg failures - never had it, guess it's mainly a result of a faulty wiring. Can be fixed with a spare in no time anyway. Result - at most you replace the reg and the CDI/IC - and here you go. As for the jumper cables - hey, I live in Russia However it's just a mess of words - I need to get the thing running in the minimal possible time, period. And the input condition is - the magneto coil is open dead. Guess nothing can be quicker then a CDI swap in this case

ps regarding the valves - why .04/.05? Had different data, from .04/.04 to .05/.10, guess the latter is better as valve clicking had never killed anything, - valve overtightening had, though

[greg]

no set them at .004 & .005 ex. blueballs is right.

[lithiumlord]

Can get pretty tricky tweking it up at an outdoor parking now Is there a chance to run it to the garage (~15km) with no failure once the CDI is swapped, or excessive gap in the ex valve can do the damage fast? (afaik it won't do any, excepting the unnecessary noise and probably some minor power loss).