Mech

Those are good suggestions Sam, especially using the snatch block to redirect the pull, people don't think of that sometimes and think their only option is one of two trees, neither of which is in the direction they want to go.

Good thanks for the reply.. I'm on a slow internet connection here and have trouble sending files..  If I could I would add manuals.. sorry. Thought I should ask about the policy. Some forums don't like links.. security or something I guess.

The combustion difference between a conventional ignition coil operation and a cdi ignition coil operation is this..

In the conventional system the 12v power goes through the coil and then to a set of points or an electronic switch which allows the power to flow to earth. That flow through the primary windings of the coil slowly(relatively slow), builds up a magnetic field which saturates the secondary windings. When we want spark we cut off the flow by opening the points or electronic switch and the magnetic field collapses quickly(relatively quickly), which induces the high voltage to fire the sparkplug. The spark is caused by the collapsing magnetic field

In the cdi system we discharge the capacitor at high voltage and high current and it induces the spark as the rapidly rising magnetic field is propagated outward through the secondary windings. The spark is caused by the expanding field.

In the conventional system, as the collapsing magnetic field induces the high voltage in the secondary windings, it also induces another lower voltage in the primary windings, and that low voltage is in the opposite direction to the initial voltage. We call this an "counter electro magnetic force", or cemf, and it has the effect of opposing the initial induced voltage in the secondary windings as well. The overall effect of this initial emf, and then the cemf, is to set up a fluctuating high voltage spark, which, if we look at it on an oscilloscope goes high, then a little lower, then up, then lower still, then up, then lower still, It typically fluctuates about six times, each times with a lower voltage, until it dies right out. So a conventional system can give initial ignition, but then as the flame propagates and causes a high pressure, the fluctuating voltage spark can get cut off by the increased pressure and fail to ignite any unburnt fuel  that would benefit from a long lasting spark. That can cause misfires or incomplete combustion.

The cdi spark is one long fat hot spark which doesn't suffer from the cemf as much and so gives good secondary ignition and less misfiring or incomplete combustion.

Ok, my two cents worth..

First off there is a difference between a cdi and an ecu/ecm. To avoid confusion for anyone looking in a manual it's important to know that some engine control module/units have a cdi system built into them and some don't.  Cdi are purely for firing the spark plug and can be built into an ecu or they can be external, and also, cdi can be fitted to engines that don't have an ecu. An ecu generally only come on fuel injected engines these days and they monitor the throttle position, the engine temp, air temp and revs, and they control the fuel injection, the ignition firing and ignition advance.

There are two different sorts of cdi. There are twelve volt cdi that run off the battery, and there are cdi that run off the crankshaft generator.

The first sort, the twelve volt ones, use battery power which they first run through an electronic circuit which turns it into an alternating current which goes through a small transformer and gets stepped up to approximately 350 volts. That high voltage gets stored in a capacitor and is then discharged through a specially designed ignition coil made to handle the very high voltage and high current which the discharging capacitor supplies. The discharge is controlled by either an ecu which has a crank position sensor, or it's controlled by a trigger coil or hall effect sensor on the crank. If it's controlled by an ecu, the ecu does a calculation of what the ignition advance should be based on revs, temp and throttle position. If it's controlled by a trigger on the crank the timing is advanced by virtue of the fact that at higher revs the magnet(or hall effect disruptor), has more effect as it's speed increases. At low revs the magnet has to get quite close to the sensor before it produces enough induced power to trigger the cdi, but as revs increase the rapidly moving magnet induces more effect and so triggers the cdi at a greater distance before the trigger, hence an advanced firing point for the cdi/ignition.

In the other sort, the crank mounted generator type, they use the alternating current out of the generator and they put it through a circuit comprised of diodes and small capacitors which "doubles" the voltage. They call it a doubler or stacker but it doesn't actually quite double, but  the voltage rises by about 1.73 times. In a twelve volt flywheel generator which has a loaded alternating voltage of about 28 volts, and up to 120 when it's open circuit, that gives about 120 effective volts. The 120 volts is then stored in a capacitor and is discharged when it's triggered by either an ecu or a trigger on the crank, and in either case the ignition advance is controlled in the same way as in the first version.

In both cases the cdi discharges through an ignition coil which is itself a stepup transformer that produces a spark of thousands of volts, 25,000 to 40,000 volts being common

The two advantages of a cdi are that it produces a hotter fatter spark, which can't be extinguished when the compression pressures go up during flame propagation, and they can fire the ignition coil at a higher frequency which allows for higher revs. Cdi systems must have a special ignition coil which can handle the high current and voltage.

I was just reading through the threads and saw a good thought for this problem...  Check the key between the crank and flywheel..  That would definitely do it.. 

And as for the original problem of frying three sets of ignition coils and cdi units..  Cdi systems have to have a special sort of ignition coil made for a high current. If you put an after market coil on there that's not made for the cdi that would blow, and probably wreck the cdi unit.

Other than that, a bad earth somewhere, could be between the stator and the crankcase(unlikely unless it's a broken wire inside there), or the engine might not be properly earthed(also unlikely if the starter works), or the coil, or the cdi unit might not be earthed. ..

Hope I'm not being a nuisance here booting all these old threads Ajmboy.. but I see there have been a lot of people looking. I presume someone will have the same problems.

Hope it's not breaking the rules posting links too.. let me know if I am. I'd contribute manuals directly but my internet is slow..

This works.

Oh ok...  I'll look in from time to time.

Had any luck with this ?

Ninety is low for one of those. It could be burnt valves or bad rings. The way to tell which it is, is to put a little oil down the spark plug hole, give it a quick spin to distribute the oil then do a compression test. Oil will seal the bad rings up quite a lot, but have bugger all effect if it's the valves. If it's the rings the compression should come up to perhaps 110 or more, if it's valves probably only 95.. It depends how bad the rings or valves are..  You could also look at the exhaust for sign of oil burning which would indicate the rings.

I suppose you have changed the fuel ? Stale fuel can make for no start by fouling the plugs even though they don't look fouled, they will even spark when they are out, but not once the compression comes on. And, once stale fuel has fouled the plugs, they seldom come right unfortunatly. You could try holding them over a butane flame and try to burn them clean which sometimes works, but often not.

If it's been sitting I'd do that and try to get it going, the compression might come better with a run.. perhaps.. by a little.. but it's not really sounding too hopeful. It's always a good idea though to try and give things a run before you strip them down so you can check the gears and crank for noises etc.. It would be a shame to rebuild the top end and then find the bottom end was shagged.. and since someone has been modifying the inlet, we'd have to suspect it's been thrashed..

The manual I have is for a 250 but I'm sure they are the same.. If the wire colours seem wrong let me know and I'll check my manuals for the colours you have. I'm in New Zealand and we have different models here..

How did you get on Billy ?

I've got the wiring diagram for that thing here and there isn't much to it. There's one red wire that goes from the battery to both those fuses. It branches inside the wiring before it gets to them. One fuse is for the auxillary power plug, and the other one feeds the key switch and the voltage regulator. The wire coming out of the aux fuse is red and white, and we can ignore that one, and the other one coming out of the other fuse is all red. That red wire coming out of the fuse branches again inside the wiring loom, and goes to the key and to the voltage regulator which I think is up near the front of the fuel tank and on the right hand side. Unless the regulator is shorting out it won't be causing the problem, and if it is shorting out it should have blown the fuse. To be sure though that it isn't shorted and draining any small amount of power that might be getting through a bad connection somewhere, it would be a good idea to unplug the regulator.. but it is hard to get to. If you can't get at the reg don't worry about it at the moment, we will diagnose it by elimination. In the meantime you should check for power at the back of the key switch, it is easy to get to. you pull a bit of plastic off in front of the dash and it's right there. There should be power to the red wire.

Since you have an electrical gauge I guess you understand how a dirty connection can let a little bit of power through when there's no load on, but then show no power when there is a load. That's why it would be good if you can to disconnect the regulator in case there is a bad connection, such as the join inside the wiring where the red wire branches. But don't worry too much at this stage about that.

So.. First check what the battery voltage is before you go checking the key, and be sure to check the battery voltage with the key off and also with it turned on. It should be twelve volts with the key off and stay near twelve when the keys on too. If the battery doesn't have near full volts in both cases you have a bad/flat battery. Then, if the voltages are ok, check the key switch red wire at the switch with the key off and it should have full battery voltage. If it does, then turn the key on and check the voltage there again.. It should be near twelve still, perhaps eleven and a half. If the voltage drops below about ten when the key is on, then there is a bad connection between the fuse and that point.

Check those things and take note of what the various voltages are at the different places and with the different key positions. You could draw up a little grid chart with key on, and key off columns, and the various test points drawn across under them.

If you have any questions or aren't sure what we are doing here holler out and I'll explain further.

http://quads.ddns.net/service-manuals/  More options..

Good name FlyinBrian..

And the compression you have should be enough to get it going..  Engines will start and run down to about 80 lbs..  60.. probably not or only with a real fast spin or tow.

If you don't grind valves it's always a good idea to tip the head upside down and fill the combustion chamber with petrol and it should stay in there.. if petrol leaks out the valves need a grind..  Simple check for next time..

Well you see the thing is, if it fires every time the crank turns, it's going to be sparking at tdc on compression, and also at tdc when the exhaust valve is just closing and the inlet is just starting to open.. right ? And that would/could cause backfiring out the inlet..  So that thing is probably set up in it's electronics to only fire every second turn, and perhaps that's your problem, and what I was trying to ascertain with all that turning back and forwards..  Try and check somehow that the spark really is happening at tdc(or a bit before), on the compression stroke...

Snap !

Hi. I'm in New Zealand and we have different models here, or different names anyway... This is a fourstroke huh ? A little quad.. And an auto clutch ? So no push start..

So the motor does turn ? It's not seized... And the battery is charged and got good power ? You could try using jumper leads and feeding power straight to the starter.. That might get the starter to work.. If not... some of those small starters they use on bikes wear out their brushes in the starter pretty regular. Or if it had been dunked the brushes could be stuck in their holders.

Not starting could be that it's not sucking the fuel in, which could be an air leak on the inlet, or a blocked exhaust which can stop them sucking.. Here in nz we have something called mason bees which build mud nests in holes like exhausts.. Sometimes the little buggers crawl six inches or more up the exhaust and block it up. You could try poking a wire up there and screwing it around, or take the exhaust off at the front and try starting it.  Once you get the starter to work you could try putting a little fuel down the spakplug hole and seeing if it will fire at least once.

Also.. how long since it last went? Did it get shut down or stop running while being ridden..

That valve timing looks right. But perhaps it's not timed to match the ignition. Have you tried turning the crank back from firing by half a turn, with the sparkplug out and attached to it's lead, and then turning the crank forwards that half turn as fast as you can with a socket or spanner? Lots of cdi will make a spark with a half turn.. If there is no spark near tdc then turn the crank till both valves are open and it's at topdeadcentre, then turn it a half turn backwards again, then forwards as fast as you can with the socket again and look for spark again.. It might be firing when the pistons at top but with both valves open, the exhaust just closing and the inlet just opening.. It's a long shot because I'm presuming the ignition trigger is on the crank, and mostly those sorts fire every rotation..but some only fire after two turns..

That should be enough compression to get it spinning, and as you say, the compression will come up once it's had a run, but if it isn't spinning even once when it pops then I'd suspect it's firing on the wrong stroke of the piston.. Also the way you describe it, as a pop, that doesn't sound like a proper firing with compression huh.. it should really make a good hard bang..

http://quads.ddns.net/service-manuals/honda/

Page 111 in the manual.

I'm not familiar with polaris at all, and wouldn't know if it's two-stroke or four, but if it is a four-stroke...Check the valve clearances. They might be closing up when it's hot causing the valves not to close properly.

Oh ok.. In that case, being that bad, and only hot.. I am thinking it's an electrical fault perhaps afterall.. an electronic fault in fact. So if you stop the motor for about five minutes, so the engine's still hot/warm, does it still do it. How cold does it have to get before it comes right again. If you have headlights you could try turning them on and seeing if it fixes it.. A faulty battery or bad battery connection could cause the voltage regulator to give you those symptoms.. 

Which brings us to...

The fact the neutral light goes dim when you're starting means there is a flat/crook battery, or a bad connection.. or a seized starter motor. First check the battery water and charge it. Check it's terminals are clean and tight. If you have an electrical gauge check the voltage at rest and again with the motor running.. It should have about 12.6 at rest, and no more than 14.7 running. Then if you had some jumper cables you could try putting positive battery power straight to the starter and see if it cranks. If it doesn't it might be a shorted/seized starter, or a bad earth. You could put another jumper from the battery earth to the starter body and try the button, or the power straight to the starter.. Try one thing at a time till you figure out if it's one of those two cables causing the no start

Oh... went back and I see it runs good cold.. good man.. bad me.

I'm assuming that when the relay clicks... the neutral light doesn't go dim does it ?.. That would be something you should mention if it did..  haha

The more details you can give us the better. I see an awful lot of expensive parts getting thrown at bikes in here to no avail, because of bad or no diagnosis.

Ok. So you say when you increase throttle.. so is this when you are already driving along, or just sitting revving it up ? And if you are driving it at the time, how much throttle do you reckon you are or can give it before it backfires ? Does it still backfire if you don't give it more than a quarter throttle say, or does it only do it when you are already over a quarter and getting nearer three-quarters or full..  We need to be quite explicit.  If you open the throttle slowly, is it better, or conversely, if you snap it open is it worse ? It sounds like in the carby or fuel supply, but we might be able to pinpoint it a bit better if you can really take notice of all these small details..  It's what mechanics do when they are road testing.. we don't just go for a blat, we try things, and take note.. hot/cold/always, lots of throttle or little, immediately we throttle or only after a few seconds, on the flat or only up a big hill or under a long load..

The starter.. you could try putting something like a screwdriver across the starter relay terminals(the two big ones), if you can find it. If that gets the starter going then it's the relay that's playing up. If bridging the starter relay doesn't make the starter spin, then it's a cable or the starter.

So tell us what circumstances it backfires under.. wide open throttle, opening throttle, inttermittently when it's idling etc, and whether it's out the exhaust or aircleaner.

Have you checked or changed the sparkplug and fuel filter ? Both good first steps probably.

The starter.. is the battery charged, does the neutral light come on, do you need to hold the clutch in to start it perhaps ? Has it been going recently or has it been parked up ?

You need to be more explicit about the problems and the circumstances.

Small 2stroke engines can warp their barrels down where the transfer ports are. It's always a good idea while you have it apart to push a ring down there with the piston and then hold the barrel up to the light and see if you can see light between the ring and the cylinder wall, then push the ring another half inch and check again.. check for warpage right through that area where the transfer ports are.

2strokes can run ok when you only get sixty pounds during a compression test. They are pretty fickle to check the compression on. once they are running the compression is often higher that the sixty.. sixty should still start.

Last time it was going did it get turned off or did it stop by itself ? Was it going good right before it stopped ?