And they're probably right. There is no rev limiter. But here is the dirty little secret: There is no rev limiter on the stock CDI either. Don't believe me? I took one of these apart and traced it out. Here is the entire schematic:



I'm pretty sure I understand completlely how this CDI works, and I don't see a rev limiter. Does anyone else?

It is possible that the timing advance curves for the stock CDI aren't absolutely optimum for really high engine speeds, and that might limit the maximum RPMs by a bit, but not by much. When they claim there is "no rev limiter" in their design my bull crap alarm is instantly activated. By claiming that they don't have a rev limiter they are implying that the stock CDI *does* has an active rev limiting circuit, which it does not.

To be clear, some quads do have rev limiters. Etons have them built into some of their CDIs, and some other quads have external rev limiters (like Baja Motorsports [IIRC]).

But for someone to claim that their CDI is "performance", with "no rev limiter" I have to ask:

Where is the test data? Where are the technical papers with published results? Who did the peer review on the data? How much increase in horsepower is there? And at what RPMs? Extraordinary claims require extraordinary evidence (in my book at least).

A couple years ago I got a private email from someone who was having battery charge problems. His battery wasn't getting charged by the battery charging system, and after a couple measurements (and several back and forth private messages) we determined that his voltage regulator wasn't working. Well it turns out he had unplugged his voltage regulator and threw it away (BTW the quad will work just fine without a regulator until the battery eventually goes dead). Someone had told him that the regulator was in fact a rev limiter and that he didn't need it. So he unplugged it and threw it away. I told him he needed to put the regulator back. I was totally amazed at how vehemently he fought me on this. He *swore* that it was a rev limiter, and that his quad was way more hot off the line after he unplugged it, etc. Wow... After he put a new regulator in, his battery was charging again - but he was still convinced that his performance was suffering. It's utter nonsense of course, but if you want to believe something human nature makes that possible - no matter the facts.

 

"He is more of a atv kinda kid.. I got him a 50cc bike and he didn't like it. Thanks tho"
The link was to a complete horizontal engine with carb, cdi, and several other acessories. I know it says pit bike on the link but if the quad you own has a horizontal engine it should work. Only thing that might keep it from fitting is if you have a down tube in front of the head or if your current head has less than 1/2 inch clearance on the sides.

 

"After he put a new regulator in, his battery was charging again - but he was still convinced that his performance was suffering. It's utter nonsense of course,"

Is a quad charging system anything like a car? I know an alternator sucks 10-15hp from internal resistance. Maybe by completing the charging circut an atv stator increases internal resistance and consumes power that doesn't go to the wheels? Even if it does would it be noticeable? Say its 0.5hp you would definitely notice on a 50-125cc but anything over 300cc only a racer could tell the difference.

 

Yes, a quad charging system is just like a car, and any electrical load on the quad stator will load the engine and consume horsepower off the engine.

But I differ with your 10-15 horsepower number for a car alternator. Let's put some numbers on this:

Power is power. It can be measured in many different units - much the same as distance can be measured in different units (feet, meters, miles, furlongs, etc). You can convert distance measurements between units (we're all familiar with this to some extent), but the same can be done for power when measured in different units. One horsepower equals 746 watts which equals 550 pound-feet per second, etc.

10-15 horsepower on a car alternator would equate to 7500 to 11000 watts, which at 70% conversion efficiency and a 14 volt DC output would equate to an alternator output capacity of 370 to 550 amps. This is way off the mark. No way can an alternator put out this kind of current...

For a car alternator 80 amps output capacity is more reasonable, and going backwards (using 70% conversion efficiency) equates to just about 2 horsepower maximum from the engine. But this horsepower drain only applies if the alternator is actually pulling off that much power (80 amps at 14 volts). If the load is less than that the alternator is easier to turn, and therefore pulls off less horsepower. If the alternator is completely unloaded (no current draw) then the alterator will spin freely, and offer no mechanical load to the engine at all.

Now for a little quad engine. My 150cc quad 8 pole high output stator (the standard issue is 6 pole) will put out an absolute maximum of 55 watts. Standard 6 pole 150cc will put out less, and 110cc quad even less still. But let's stick with my 150cc quad for now. 55 watts going backwards (using 70% conversion efficiency again) will pull off 0.10 horsepower from the engine. But again, this assumes I'm pulling off the maximum possible power. This isn't real life though. Most of the time I'll be tooling around with the headlights off, the brake light off, and the battery is already topped off and fully charged. Thus my entire electrical load to the engine is the ignition system wattage only, which is about 3.5 watts, plus the battery trickle charge which is about 1 watt. So 4.5 watts is about 0.009 horsepower. This is getting ridiculously small, and I think can be ignored when looking at the big picture.

 

Ok i ordered them ill try it out... who cares its only $50... side note my sons stator just failed again.. same old thing too.. first head lights stopped working... now no sparke we have 3 of these 90cc and 110cc motors all are the same so i can swap parts while testing and trouble shooting them... and again the stator failed.. are these just junk or is there maybe somethind i'm missing.. Lynn you are an amazing helpful person and you have saved me in the past can you help me again?
Thanks
Steve

 

Let us know what you find. I'm curious to see if you see noticable improvements...

This is strange indeed. Your ignition system uses a five pin CDI (from info in an earlier post), and therefor your ignition system runs off moderately high voltage AC from the stator. Your head lights run off a completely separate low voltage high current winding in the stator. If your lights are AC powered this is directly off the low voltage stator winding. If your lights are DC powered then they run off the battery and the recitified/regulated low voltage winding from the stator. These two windings (high voltage and low voltage) have nothing to do with one another. They are totally separate from each other. There is also the ignition trigger coil (also from the stator) which is yet another (third) separate coil winding. This too can prevent spark, but doesn't have anything to do with battery charging or running head lights.

So the scenario where the lights stopped working, and now no spark, doesn't make sense to me. They cannot be related. Some questions:

Are your headlights DC powered or AC powered? When the headlights failed, what about the tail lights? Did they fail too? What about the brake light? Did it fail too?

When the spark failed did you do the standard "no spark" tests for a five pin CDI? If so what were the results? If you didn't do the tests I would strongly suggest that you do these tests on a stator that doesn't produce spark. It will shed a lot of light on the problem I bet.

Here is the generic test suite for a five pin AC powered CDI:

 

Lynn we have two of these atvs, I had this issue in the past. I took of the stator from the one that was running, after putting on the one with no spark, got it to start with no problem. I am asumming these are just bad parts, and or my kids are to rough on these little 110cc atv's. the stator smells cooked and looks bunt up also.

Side note CDI and Coil should be here with in a few weeks, Ill post and update after install and a few hours of breaking it in.

 

Whoa ... That is important information. The output power from your little stator is inherently limited, and cannot burn itself up do to some excess electrical load.

Think about how a stator works: You move magnets across a coil of wire and it generates a voltage. If you apply a load across that coil, current flows which generates a magnetic field in the coil that pushes back against the engine making it harder to turn. Mechanical power in (usually measured in horsepower) is converted to electrical power out (usually measured in watts). But power is power, and they can be equated. One horsepower equals 746 watts. Watts and horsepower are just two different ways use to measure the same thing - i.e. power. More load on the stator output means a larger "push back" magnetic field from the stator coils, and means the engine gets loaded down more. There's no free lunch. Power in equals power out.

So as you increase the load on the stator with the engine spinning the increased output current causes a bigger magnetic field to be generated in the stator coils, which pushes back harder against the magnets in the flywheel making the engine harder to turn. But at some point the magnetic field generated in the stator coils *equals* the magnetic field coming in from the magnets in the flywheel - repelling all influence from the flywheel magnets, and here the output power reaches a fundamental limit.

This is the important part: That fundamental output power limit is *way* below the power necessary to char and burn a stator. So we need to look elsewhere...

The most common way a stator gets burned up is when the voltage regulator fails shorted, and the quad battery is then hooked up directly across the battery charge winding in the stator. Current flow backwards out of the battery into the stator winding limited only by the stator coil resistance. [Normally on a working voltage regulator the rectifier diodes in the regulator prevent this backwards current, but these can often fail shorted.]

Consider the following possible scenario:

1) The regulator fails with shorted rectifier diodes.

2) The battery starts discharging backwards through the stator at about 20 to 30 amps or so (that equals 240 to 360 watts, or roughly a third to a half horsepower of power.)

3) The stator starts getting massively hot - but since it is inside the engine you don't really notice anything yet.

4) The battery will go dead in 5 minutes or so, but the engine is still running. Since the engine ignition system is powered off the *other* stator coil which is only getting cooked indirectly from the battery charging coil, the engine runs for a while.

5) The battery, and battery charging system are now kaput. Lights (or anything else 12 volt powered) don't work anymore. But the engine still runs...

6) Finally the heat migrates over to the stator ignition power coil and wrecks it too. Now no more spark.

Does this sound plausible to your situation?

But for this scenario to play out you also need one more bad thing: No fuse, or the wrong fuse installed in the wiring harness feeding everything off the battery other than the fat heavy gauge wires feeding the starter motor through the starter solenoid. Do you have a fuse? It should not be greater than 7 amps on a 90cc - 110cc quad. With a proper fuse a shorted regulator will just pop the fuse - no further damage should occur...

 

I was having problems with bad, out of the box, CDIs. Lynn Edwards helped me with that, however I did buy a Hi Po CDI and coil, but I never put them on. They are still sitting in my desk drawer.
The last GOOD CDI I put on allows the engine to rev an ungodly amount of rpms and I just don't see how anything could make it do more.


So many rpms it shook the screws out of the bowl of the carb. .. If anyone has any extra screws please let me know.. I need them. I have a Sunl 110cc 3 screws holds the bowl on.

 

Sorry Lynn but your way off on your engineering math of alternator parasitic loss. One thing I never saw you mention is DING DING DING acceleration. Steady loading, which is what your math refers to is basically irrelevant. Acceleration is where perceived power comes from. I deal with high hp engines on a regular basis and parasitic drivetrain or acc loss is always at the forefront of your mind when your hard earned dollars are creating each hp. The same, say, transmission will consume different amounts of parasitic power with a 300hp engine vs a 750hp engine. By your math it would be insignificant, but infact it is a very significant difference.....but not necessarily at a set speed or rpm.