Better CDI units??

ddyk,

Can you think of any reason why grounding the white wire (lighting coil) to stop the engine would cause any harm to the CDI? Been instructing dozens of customers to do this, and have only encountered a couple of CDI failures which were probably due to leaving the bike outside in the rain.
 
Certainly not,that is nonsense,if it stops the engine it's about the safest thing you can do as far as anything else is concerned.The blue wire is a bit more iffy(Higher voltages higher impedance level esp,in the series mode),if the WW works don't mess around with the BW.I think most problems have to do with moisture penetration into the pulse output transf.inthe CD, resulting in tracking & eventual failure.The generator output could be marginal too (wide spacing)If you have a marginal system to begin with anything can be blamed,but the root cause may be elsewhere ! I forgot one thing,if the WW does NOT stop the engine(unlikely) and you keep the switch closed you may fry the winding thus opening up the ground return for the coil,then paradoxicaly the ignition can only work with the kill switch closed!!
 
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ok so today i have been fiddling with just about everything, firstly i have my fuel tank mounted on a rack over the rear wheel. i made sheetmetal box to go over this then mounted the CDI on there. i then opened the magneto cover and removed the wires one by one and replaced the wires with a better quality automotive wire, i then soldered these to the wires coming from the CDI. i then made a new longer spark plug lead and bought a new end for it. made the lead froma good 8mm car lead that i bought just for the job. now with the CDI mounted under the box it is out of the elements and should not get any dirt etc on it. i then test rode the bike but the problem was still there. i went over to the local mower shop and spoke to the guru there, we replaced the chinese spark plug (after many trial and errors) with a NGK B6S plug. test rode the bike again and the engine ran smoother but still broke down at higher revs. (only getting about 30kms an hour out of it) i then took it home and drained all the fuel from the tank and lines and carby and replaced with a mower mix sold at the local servo. test rode it and got a better response. (the fuel is mixed at 25:1) so i removed the baffle from the exhaust pipe and rode it for about 10 mins and the engine began to smooth out and i almost got my top speed of 55kms back. went home and removed the plug. (wasnt fouled) reduced the gap and put it and the exhaust baffle back in then rode it again. the engine was fine for about 10 mins then started to misfire at high speeds again. so i stopped and pulled the baffle out again and low and behold after 3 mins it smoothed out again. when idling the engine surges and will rev low then increase then drop again. so i pulled the carby apart and cleaned it out. put it back together and no difference. i again pinched the CDI off my wofes (perfectly running bike) and the bike again ran absolutly perfect. top speed of........wait for it...................65kms thats right. you heard it. 65kms.. so i went to the local Motor bike shop and grabbed a second hand CDI off a Yamaha YZ 80 and replaced the plug lead with the one i made. then wired it up and hey presto.. perfect running bike that does 60-65 kms....... see how long it lasts. hopefully it wont burn out on me.
 
just been for a ride again for bout 45mins. everything seems to be running fine. the only thing i have found is that it is a little harder to start and wont start with the choke on. just pump the carb bout 10 times then start peddalling. fires a few timees whilst peddling then goes easliy after bout 15 seconds. warms up after 2 mins then wow. the 80difference is unbelievable... and the best part is the guy sold me the YZ 80 CDI for 5 bucks. let you know how it goes after sitting all night.
 
Right on. Thank you!! This is a hard to kill myth.

I've been trying to kill it for a while now, figured having an EE's opinion might give my argument more weight. I think that some no start problems are because water gets into the kill switch and when you use the blue wire (high voltage), there is enough leakage current to kill the spark. If you use the white wire, the six volts isn't enough to cause any appreciable leakage current.

dan48cc said:
so i went to the local Motor bike shop and grabbed a second hand CDI off a Yamaha YZ 80 and replaced the plug lead with the one i made. then wired it up and hey presto.. perfect running bike that does 60-65 kms....... see how long it lasts.

How did you wire that CDI? All of the motorcycle ignitions I have seen require a separate trigger coil. I am working on a Honda C90 based CDI solution for our bikes, and the most difficult part is mounting the magnet and trigger coil precisely for correct ignition timing.
 
the unit i got came off an 78 model YZ 80 and only had 2 wires, one black and one white. i assumed that the black was the ground and the white was the power. i guess it wwas right. been riding it for a week now and it has ben running better, i also get less interference to my electronic speedo. the bikes top speed is awesome. i can fly past traffic if i hammer it. ( speed limit is 50kph) also igured out that the hard starting was the result of the nw spark plug. cleaned up the original plug and it starts first time again and runs perfect with no fouling. if you can get hold of the cd unit i got then maybe it is an alternative. i will pos some pics soon as i ge my new card reader for you all to look at.
 
Cool find.

The Honda CDI's have a separate trigger coil, and an external ignition coil. If you found a two-wire integrated CDI/coil pack, then you are certainly on to something!

The Yamaha's I have worked on have a similar arrangement, I thought the YZ80's had a similar setup.
 
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Getting the trigger pickup right is going to be hard to pull off.Then there is the compatibility (or lack of it) between the generator outputs.It might be easier to redesign the CD unit.I think it is marginal components&inadequate hermetic sealing that plague them,has the hallmark of progressive insulation failure to me.
 
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