Better CDI units??

Discussion in '2-Stroke Engines' started by dan48cc, May 11, 2009.

  1. dan48cc

    dan48cc New Member

    ok so my bike is 3 months old and i am on my third CDI Unit. i have moved it fiurther away from heat made a sheild to put it in to keep away heat and draw in cold air. i have made my own lead from a new car plug lead but yet i keep killing them. i asked the supplier and his answer was simply that they make good batches and bad batches. this for me is not good enough i use the bike as daily transport. can a CDI be retro fitted froma motor bike or an ATV or scooter or the likes. has anyone done this. i have a cdi from a yz 125 here with all the same wires etc. however will the output range. being it is from a 125cc be too strong for my 48cc engine. has anyone got any ideas i am sick of forking out 30 bucks everytime mine dies.

  2. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    I have sold 100's of these 2 stroke motor kits and maybe
    had one bad CDI. They are very reliable.
    I have replaced a few CDI's on others used engines.

    Where did you buy your kit from and who is your supplier?

    The grubee kits that I sell now come with a 90 day / 3 month warranty
    so it would not have cost you anything and $30 is kinda steep for a CDI

    I doubt if CDI's from other motor bikes or an ATV or scooter will work

    Only thing I can think of is that your magneto is killing your CDI's
    How is your kill switch hooked up? What wires did you use? maybe that is
    killing them?

    A long custom spark plug lead could remote the CDI but i don't think that
    is the problem

    Good luck, let us know if you figure out what the problem was

    PS: This doesn't belong in the BICYCLE Repair & Modification section
  3. dan48cc

    dan48cc New Member

    i bought my engine kit from the sellers name was mrbikeboy. he offered only a 30 day warranty and the first cdi went 3 days after warranty and the second did not come with a warranty and the third was just never that good. when i first got the bike run in it would do 55kmh now it struggle to reach 35kh i put the cdi off my wifes bike on mine and it went great again doing 55kmh. i wired the blue cdi to the blue engine, the black cdi to the black engine and the white wire to the yellow/red wire then the green to the earth on the bike frame. i have no other dramas with the engines at all. as a whole an awesome package. just these **** cdi units (lol) the price i am getting charged for a cdi is $25 au plus $5 au postage. there just has to be a better solution..
  4. dan48cc

    dan48cc New Member

    PS. sorry bout the wrong post, and the new lead i made is only 5cm longer than the original on and provides a stronger spark
  5. fetor56

    fetor56 Guest

    George from MBB Imports is a decsent enough person & most of his parts are Grubee;their ok.
    Try not using your white wire as a kill switch,use it for lighting power only(or don't use it at all)
  6. fetor56

    fetor56 Guest

    BTW...dunno of ANYONE who has successfually swapped to a different type of CDI.
    Do we have a crash-test-dummy. :whistling:
  7. jlebh1

    jlebh1 Member in adelaide sell performance ones there a bit more expensive but they seem to look better they also balance every engine crank and have a hp engine with porting and polished
  8. Junster

    Junster Member

    I'm thinking you may have a wiring problem. I'd check the mag first for any stray wires in the winding sticking thru the cover wrap. Make sure the black wire is solidly grounded to the mag frame and that when the motor spins the mag frame can never contact the spining magnet. I'd also try removing all the plug in connectors and soldering the connections. My kill switch is to white and the other side is directly to black not the frame. To kill 3 cdi units it almost has to be getting a power surge. Good Luck.
  9. spad4me

    spad4me Member

    Use a killswitch that opens the blue wire circuit.
    Solder and tape everything.
    Seal the spot where the wires exit the magneto chamber with Goop or silicone.
    I have worn out one steel frame in about 24 months time.
    Never had a problem with a cdi or magneto .
    Now the chain is another matter.
  10. duivendyk

    duivendyk Guest

    The CD unit is one element in the Ignition system,the other is the generator coil which supplies the pulse power to it.This is unusual in most systems there is only one composite unit.This makes it next to impossible to find a more reliable replacement.
    Normally ignition coils are hermetically sealed,moisture penetration can cause high voltage transformers to fail over time.This CD unit is probably not adequately protected against this.It should be mounted so all the leads and come in frombehind and from underneath.Silicon rubber should be used to provide the best seal's probably a good idea to put it in a low heat oven at low heat 125 degree F for a few hours first to drive out any moisture.Also never ever crank the engine without a sparkplug connected and with the shell grounded.I think the output pulse transformer is the most likely to fail component.So don't overstress it.Another possible culprit is the energy storage capacitor .If your generator coil had a higher than normal output it could over stress the cap,or it could be marginal to begin with.Insulation breakdown is a gradual process first some current leakage then catastrophic breakdown.Whatever has been done that could affect the generator coil performance,leakage at the killswitch esp if the blue wire is involved instead of the white wire,may affect a marginal system.Which is then mistakenly attributed to the CD unit.Sometimes the spacing between the flywheel magnet and the generator coil is too wide.This reduces the output to the CD unit.A thin calling card should just fit,if too wide,reposition the coil &bolt it down securely. Good luck.
    Last edited by a moderator: May 12, 2009
  11. arceeguy

    arceeguy Active Member


    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.
  12. duivendyk

    duivendyk Guest

    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!!
    Last edited by a moderator: May 12, 2009
  13. Pablo

    Pablo Motored Bikes Sponsor

    Right on. Thank you!! This is a hard to kill myth.
  14. dan48cc

    dan48cc New Member

    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.
  15. fetor56

    fetor56 Guest

    Yamaha YZ 80 CDI....hope this is an alternative;if it isn't please let us know.
  16. dan48cc

    dan48cc New Member

    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.
  17. arceeguy

    arceeguy Active Member

    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.

    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.
  18. dan48cc

    dan48cc New Member

    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.
  19. arceeguy

    arceeguy Active Member

    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.
    Last edited: May 21, 2009
  20. duivendyk

    duivendyk Guest

    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.