QT50 only runs on aftermarket CDI

Garrett Jackson /

I have a QT that will only run on the cheap blue CDI in the picture. I can take a stock CDI off my other running QT and it won't start. Any idea what's the problem?

Screenshot_20210329-193705.png

Re: QT50 only runs on aftermarket CDI

Are you sure that the wiring is the same?

Do you have spark with the stock CDI on this bike?

Re: QT50 only runs on aftermarket CDI

Are both the same year...some have start run feature on the ignition and some don't..

Re: QT50 only runs on aftermarket CDI

Garrett Jackson /

Both are 79s, so there's not a start/run feature. The wiring is the same on both bikes - they are identical except that one has an aftermarket coil and the other has the stock coil. It seems that the blue aftermarket CDI produces a much stronger spark on the bike, but the stock CDI does produce spark. And as I mentioned, the same stock CDI runs the other bike perfectly. Just to reiterate - I can take a stock CDI from a running QT50, put it on another QT50 and that bike won't run, but that bike will run on the blue aftermarket CDI in the picture.

Re: QT50 only runs on aftermarket CDI

Not sure it would make a difference so just trying to eliminate things and as you know strange things can happen..do you have the same plugs in both ?..try switching the plug also ..maybe one resistor and the other.not? Or plug cap ? (edited)

Re: QT50 only runs on aftermarket CDI

Just curious, will the aftermarket cdi run on the bike that you took the stock cdi from?

Re: QT50 only runs on aftermarket CDI

$20 bucks it's the charge coil. The 79 had a faulty charge coil when bad caused poor or no spark. Sound like the new cdi can uses a lower voltage. Look at your coils if you have the white one on top change it. The charge coil runs the CDI. (edited)

stator.jpg

Re: QT50 only runs on aftermarket CDI

just glad you cound a after market cdi,that makes me shy away from some bikes because they are unobtainium.

Re: QT50 only runs on aftermarket CDI

> Garrett Jackson Wrote:

> -------------------------------------------------------

> they are identical except that one has an

> aftermarket coil and the other has the stock coil. It seems that the

> blue aftermarket CDI produces a much stronger spark on the bike, but the

> stock CDI does produce spark. And as I mentioned, the same stock CDI

> runs the other bike perfectly. Just to reiterate - I can take a stock

> CDI from a running QT50, put it on another QT50 and that bike won't run,

> but that bike will run on the blue aftermarket CDI in the picture.

I am not surprised that when you mix and match ignition coils and CDI boxes there are some configurations that don't work...

Re: QT50 only runs on aftermarket CDI

PW50 charge coil $20 ebay Moose racing.

Re: QT50 only runs on aftermarket CDI

https://www.treatland.tv/MB5-yamaha-chappy-qt50-suzuki-fa50-flywheel-puller-p/27mm-flywheel-puller-reverse.htm

Going to need this any way, swap the stators and see if the problem swaps. (edited)

Re: QT50 only runs on aftermarket CDI

i'm with arlie, i would guess the charge coil or something is weak in the one system, too weak to blast off with the old stock bits, but the newer box has enough amplification or whatever to tolerate weaker feed

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