90cc atv/ no spark

[micscience]

Hey guys I posted here because I can't find any atv related forums. At least not on this level with so many users. I have  a 90cc atv all the electrical is pretty similar to the gy6 so I figured I'd give this place a shot.

I have no spark, the stator is good and new. I measured the voltage coming from both voltage producing wires blue/white wire and black/red wire and the voltage is within spec. The coil is brand new, the plug is brand new and I'm pretty sure everything is grounded I tightened the engine ground.

Basically when I go to measure the voltage coming out from the CDI to the ignition coil there isn't any. It only shows voltage when I stop cranking for a second which is weird. When the engine is cranking I don't get anything and I can't figure out why. The only thing I can think of is the wiring. Like maybe the grounded black wires which are twisted together into a junction isn't good but I traced all the wires which carry voltage and I don't see any damage to them.

I would hate to buy a new wiring harness and install it for the same issue to occur. Any help would be appreciated. Thanks

[90GTVert]

At least with meters I've used, I can't see voltage to the coil on that wire when everything is functional.

Try checking the kill wire on your CDI. Usually a ground is applied to that wire to shut off the ignition. If any ground is present with all safety switches in run positions (ign and kill switch), then a switch may be malfunctioning or you have a short. Otherwise, it sounds like it may be a CDI. You can probably find a CDI to test with cheap on eBay. It's a good thing to have around because you can't really test a CDI any other way (aside from an expensive specialty tester).

[micscience]

I don't understand how one couldn't read voltage under AC current in the meter since it is a decent amount of voltage going to the ignition.

I have 4 CDI's and 3 of them are brand new. I tried every single one.

As far as the kill switch goes I'm pretty sure the engine wouldn't crank if the kill switch was bad though I'm not familiar on how these atv's are setup If I have a short it's going to be a pain to find. I should just get the damn wiring harness it is only $20 something dollars. I'm going to look for a short or a missing ground one more time. If I can't find it I'll buy the harness.

[micscience]

You're right I tried measuring the voltage on my scooters outgoing CDI wire to the coil and it does the same thing it doesn't show voltage except when you let go of the start button.

[GrumpyUnk]

To my level of knowledge, there are two basic forms of CDI. AC operated and DC operated. The latter, DC, will only work if the machine has a battery that is charged. The AC style should operate the ignition when the engine is kicked over with the kick starter, battery disconnected.
Looking at the peekshures I cannot tell them apart, except that scooters all seem to need the 6-pin style, 4-2 connection array.
If you poke around, you can find which pin provided ground(from ignition switch/kill switch) to stop the CDI from working, and then remove that connector(most have a bendable prong that can release the metal connector from the plastic surround) and see if you get sparky. If so, then start looking towards the switch end of the machine, up towards the handlebars where the switches reside. You may find a shorted 'kill' wire that is grounded due to chafing of the insulation.
If you are getting the AC voltage from the stator, and the 'trigger' from the stator, then the CDI should send a pulse to the coil to make things spark. You do need both the 'power' and 'trigger' signals. The trigger is(on GY6/139qmb) mounted near the 12 noon position where it senses the little tab of metal on the outer diameter of the flywheel. If it is broken, too far away, or flopping around, it won't signal the CDI(trigger) to fire, and again, no sparky. The AC generator is a winding inside the flywheel, and you have to look at the individual wire(not yellow or white from memory) that leads to the CDI to put a VOM on to sense the pulse of voltage that excites the CDI.(while cranking)
Look at the individual 'things' that it needs, eliminate the ones you can test, and then call Sherlock and Dr Watson to eliminate the impossible. Oh, wait, I have that wrong. Eliminate what you can, and what remains is the solution(hopefully).
I doubt you have 3-4 bad CDIs all at once.
tom

[micscience]

Ok first off thank you. Even if I can't figure this problem out that information is most helpful. Now I think I know why my scooter is unable to start with the foot crank when the battery is dead. I'm assuming I have a DC setup. I always thought my scooter was AC due to the headlights getting brighter with throttle response but that I guess happens with DC as well apparently which I didn't know.

Now as far as the ATV goes I have a black/red wire plus a blue/white wire I measured both signals which I believe the pulse is .4 volts and the other wire is reads much higher in voltage it is definitely within spec. The way my stator is assembled it seems impossible to adjust the little black coil pickup like in a scooter. It is positioned in the opposite way of a scooter the flywheel's inside is facing outward away from the engine and the stator is covered by the case that attaches to the engine. However I do get good voltage anyway so I should be good there.

I can read the voltage going into the CDI and maybe those spurts of voltage is the pulse when I let go of cranking. I think removing that ground wire from the CDI plug is a very good idea. The atv is missing it's engine mount bolts and it is out of position. I'm wondering if that may have caused damage to the wires. I assumed the kill switch was fine since it lets me crank maybe there is voltage drop or the wire has only enough integrity for cranking. Thanks again I will update what happens when I try it.

[FrankenMech]

The Kill switch does not have anything to do with cranking. The Kill switch grounds a terminal on the CDI that kills the spark output.

[micscience]

I unhooked the wire from the kill switch to the cdi nothing changes it cranks without spark. I'm giving in and buying a wiring harness.

FrankenMech- I disagree try starting/cranking the engine with the kill switch in the off position.

[FrankenMech]

The engine will 'crank' with the kill switch in any position on most scoots or ATVs. It just won't start if the CDI pin is grounded.

Cranking and starting are not two words for the same thing.

If you don't have the skill and knowledge to get your existing wiring to work what makes you think replacing the entire wiring harness will help?

Take the ATV to a shop where they know what they are doing. Wiring for these vehicles are EXTREMELY simple.

[PirateLabs]

FrankenMech is correct.  My scoot cranks with the kill switch off...it will just not start that way. Not long after I got my scoot I was out in the middle of nowhere and when I went to start it...it cranked away but did not start. I figured...great...now I will have to push this all the way home and then realized my kill switch was off. Opps...switched it on and boom...started right up. I was very relieved to say the least.

Bill

EDIT:  I remembered incorrectly.  I just installed my new CDI and, I tried cranking the starter with the kill switch in the off position and, nothing happened.  I flipped it to on, and it cranked.  So, I must have remembered wrong in that it would not even crank and I thought I was going to be stranded out in the boonies, not that it would not start.  Sorry about remembering wrong.

[FrankenMech]

Some kill switches have a set of contacts that can be used to interrupt the starter circuit but from most of the schematics I have seen it is rare. It adds needless complexity but I suppose some morons figure it adds to theft reduction. I always go for simplicity, the more wires and switches involved the greater the chance for failure. My scoot was a nightmare before I rewired it.

[micscience]

Almost every scooter, atv, motorcycle has a kill switch connected to the power/starter circuit. It's not a mystery that there is also a wire going from the kill switch to the CDI but most bikes will not crank with the kill switch in the off position. I'm surprised you didn't know that. That is why when you open up a kill switch there are 3 contact positions for the kill switch button. If it was just connected to the CDI there would be 2 contacts not 3.

("If you don't have the skill and knowledge to get your existing wiring to work what makes you think replacing the entire wiring harness will help?")

FrankenMech if you didn't know how a kill switch worked I doubt you're qualified to judge if I'm skilled enough or not to fix my quad. It's called troubleshooting for a reason.

[FrankenMech]

I know how most kill switches work, they can be wired into scoots or other small engines in many ways. Some are overly complex. Most of the scoot diagrams I have looked at went for simplicity, or fewer wires == cheaper and usually more reliable. The only thing a kill switch needs to do is ground the ignition system. There is no 'good' reason for the kill switch to interrupt the starter circuit other than to keep stupid riders from running the battery down.

I just question whether you are skilled enough to replace an entire wiring harness if you can't troubleshoot and fix a few wires and connections in a simple no-start condition small engine CDI ignition system.

Before you rip out the entire wire harness find yourself a service manual and follow the troubleshooting diagrams.

Using a manual is a whole lot easier and quicker than shotgun parts replacement directed from the internet.

BTW, my original kill switch circuit was wired to interrupt the timing pulse to the CDI rather than ground the kill circuit from the CDI. The reason that was done on my scoot was 'convenient' in that there was also a rev limiter hidden near the handle bars that was activated by a suspension lock switch or by high RPMs themselves. I removed the rev limiter and rewired the kill switch to just ground the CDI kill circuit. The original circuit was certainly overly complex but there were reasons.

[micscience]

I just don't find installing a wiring harness hard to do. I have done it numerous times.

I don't see why a wiring harness wouldn't fix this issue or at the very least be very helpful. If any plug is bad it will get replaced. If any ground connection and I'm talking about the combined ground wires that are soldered together at the junction in the middle of the frame if any one of those are bad it will fix that issue. Plus from using generic plugs I can now use the OEM plugs. On top of that the battery wires are not in the best shape they have that whitish corrosion look to them and finally the color coding will match.

I would love to have a wiring diagram shit I have searched all over the net but there arn't any. It's pretty similar to a gy6 so I use one of those crappy simplistic ones that don't tell you the color of the ground wires

Everything has been verified, voltage is good, resistance is good, stator is good, gap between the pickup is good enough according to voltage readings. There has to be a bad ground some where or there could be voltage drop.

A young 9 year old owns this atv and I'm fixing it for him for free though he didn't make it easy by messing with the wires.

[FrankenMech]

Ground wires are usually green, green with a yellow stripe, black, or even occasionally brown. Wire colors are always a crapshoot when anything from Asia is concerned. Print a somewhat similar schematic out and note the colors and changes on it by hand. Find the bad ground. Add a frame ground stud or connection that you can bring ground wires to for secure connections. The unit ran at one time with the existing wiring.

Many scoots and ATVs are made into 'basket cases' by owners messing with the wiring, vacuum tubing, fuel lines, etc. Frustration leads to abandoning the 'project'. A lot of skilled people buy those basket cases for cheap or even free and then fix the connection or other flaw then 'flip' the unit for $$$$. The wiring and other systems on these units are really very simple for anyone with skill and experience.

ATV/scoot wiring harnesses seem to come from the lowest cost supplier that uses whatever color wire they have. The wires are small, brittle, and poorly insulated. Connectors are cheap, poorly crimped on, made of crap material, corrode, and won't hold a connection due to bad metallurgy. There is more to making a good connector than taking some dirty brittle copper and flash plating it with gold to give the illusion of quality.

Asian wiring is like the old German VW wiring, -very poor. Re-working connections seems to be the major difficulty.

Good luck!