motor dies when hot

feel the CDI immediately after it dies. If it's warm, it may be cooking itself enough that resistance is too high to fire, same with if you're running too hot of a plug (though not likely). These CDI's can be known to cause issues.

Otherwise the only thing I would think is the better atomization as it warms up is causing it to run too lean. Does it start right back up when it cools off? Try playing with the choke lever after it dies. Choke on will richen up the mix and cool the engine off faster.

When electrical components get hot they can develop an open circuit or a short.
Before digging into the ignition components, I recommend doing the following test at night when the spark will be easier to see.
Check for spark while the engine is hot and has failed. Do not use the spark plug that is in the hot engine as removing it while the cylinder head is hot can easily ruin the threads in the head. Carry a spare, known good spark plug for testing purposes.
Do not lay the test spark plug on a painted surface as the paint will act as an insulator.
The spark plug must have good metal to metal contact with the engine.
If there is no spark the first suspect is the spark plug itself. After the engine cools try installing the test plug. Also of high possibility is the factory spark plug boot on the end of the high voltage spark plug wire. The factory boots are well known for poor design and fall apart on their own.
The easiest and most dependable repair for a bad spark plug boot is to use a known good automotive ignition wire.
Here in one of many threads about changing the wire:
http://motorbicycling.com/showthread.php?t=33185
If that fails to fix the problem then it is time to get a multimeter and check the ignition components. Check 2door's post, #4 in this thread:
http://motorbicycling.com/showthread.php?t=27629

I'd first get rid of that 'light power unit' if it runs off the white wire - these have often caused strange problems.

In my last post I failed to mention that the spark plug's electrodes should be gapped to approximately 0.025"/ 0.635mm (acceptable variance of + or - 0.001" or 0.0254mm).

The easiest way to check for spark is to remove the spark pug wire from the spark plug.
Connect the spark plug wire to the test spark plug and lay the test spark plug on top of a cylinder head nut. The metal hex part of the spark plug, the area which you put a wrench onto the spark plug to turn it, is the part that needs to make contact with the cylinder head nut. Use a neodymium magnet on the cylinder head nut to hold the spark plug in place of necessary. As your engine will still be hot when doing this, wear gloves to protect your fingers!
Ride the bike like you are trying to start the engine, using pedal power to crank the engine over. Being careful to keep your balance, look down at the spark plug to see if you have spark. As said earlier, this is best done at night to make seeing the spark easier.

Save yourself $ and labor time and test for failures before replacing parts. There is no sense in replacing a good part.

By "light power unit" I thought he meant the second piggyback coil made by wonderfulcreations/ mightywonderful on ebay.

Check for spark - Remove your spark plug. Connect the spark plug wire to it again. Rest the little tab at the bottom of the plug on the engine head somewhere (to ground it). Crank the engine over. You should see a spark.
I agree with these guys that it is likely the black ignition box, the one the spark plug wire come from. You need to check for spark as soon as possible after the motor quits on you.

Were is your CDI in relation to the engine?
If it right by the exhaust pipe that will cause it to get hot.
Keep your CDI as far away from heat as you can.

Also, unless you are in the arctic a 5 plug is way to hot for summer, you need a 7 or so.
Whether this fixes you or not I urge to get an NGK 5944 (BPR7HIX) Iridium spark plug.
I haven't used a stock plug in any 2-stroke I've built for years, they all get the 5944, sick bikes has them here.

http://www.sickbikeparts.com/catalog/product_info.php?products_id=141

The center number on an NGK is it's heat range, in short how much heat it dissipates to the head or keeps in the engine.



The more white you have in contact where the threads are, the more heat is transferred to the cooling fins, and the pink is just providing an air gap to keep heat in.

I would also have to argue that an air cooled motor dissipates much more heat much quicker in a freezing wind opposed to a frigg'n hot one.

----
Engine Speed and Load

* If the engine is to be operated at high RPM, under a heavy load, or at high temperatures for long periods a colder heat range may be needed.
* Conversely, if the engine is to be operated at low speeds or at low temperatures for long periods, a hotter heat range might be needed to prevent fouling.
----

The basic rule is go as high a number as you can until you get plug fouling from it not staying hot enough.

Hope that helps.

Jonda500 said:

Thanks for your help everyone! I am in the middle of winter here in Australia so the temperature I'm riding in is between zero and 15 degrees centigrade.

Click to expand...

Then a 5 should be the right plug ;-}

The wonderfulcreations lighting coil should not affect the ignition system as it is an entirely separate coil that is not connected to the ignition circuit at any point.

that's great news. Keep on ridin My recommendation though, to save your bearings (and thus your motor, and who knows, maybe even yours) life, drop the $80 or so on a Jaguar CDI or Lightning CDI. They have ignition retard at high RPM to reduce cranking pressures and save your bearings. Particularly the conrod bearings.

Jonda500 said:

I just bought a nice looking no white wire magneto stator coil on ebay for $10, fingers crossed that it will solve my issue once and for all!

Click to expand...

All the new skyhawk kits come with no white wire mags.

Thanks for the update, glad you got it fixed. The mag coil lives in a hot and vibration filled environment compared to the CDI. It makes sense that it went bad first.

The newer 'no white wire' mag's seem to be a better and may even help when it's a weak magnet issue.
Just out of curiosity, when you put the new mag on, did it go on easy or did you have to really fight the magnet to get it bolted in?

Hopefully the latter was true for you as a weak magnet is an actual problem it took me a whole day to find on a brand new build.

For future reference this my electric system test procedure.

My troubleshooting procedure is simple these days.

Disconnect everything.

Ohm the black magneto wire to a head bolt, it should read a dead short.
If not, check the ground tab on the magneto.
Note:
The new skyhawk CDI's have no white wire, ground is the lower connector but it has a wire from it to ground.

Old style mags with a white wire have a tab out of the mag that solders directly to the mag base for ground and they can come loose, just hold it down and re-solder.

Ohm the magneto from the black and blue wire, 320-380 ohms is ideal, an open or dead short means a bad magneto if the wires are connected.

Ohm the CDI in the 10K-20K scale.
Red+ meter probe to CDI black wire.
Black- meter probe to the spark plug cap.
You should get about 6.9K ohms.

If not it could be a bad wire or cap.
Unscrew the plug wire at the cdi, use pliers or even cut it off and dig the junk out if need be and do the same test above again to the cable screw on the CDI.
If that works get a new wire and plug cap, if not you have a bad CDI.

If all of that is good there is only one thing left, the magnet.

That was indeed the problem with this repair on a new build with a 2014 gasbike.net front page engine kit.

When you pull the 4 bolts out of the magneto mount it should slam itself against the magnet, I mean to the point where it is hard to even get your first bolt in.
A weak magnet that lets you move the mag around pretty easily is not strong enough to create a spark which is what this repair had.

Magnet replaced, problem solved and my repair is done.