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Discussion Starter · #1 ·
hi

I have this cheap XR500R from 1983. I bought it as non running and it has nighmare electric system and spark is weak as hell and very occasional. I dismantled the motor during winter because there was very little compression when kicking the engine.

I used various methods to fix it as cheaply as possible. Made own gaskets. Welded the cracked cam gear, joined two old TLS cam chains together and made new chain out of them. Also the piston pin was little scored so we lathed a new one.:devious

polished the valves to get good seal and looks like now there is a nice compression in the engine. But I need spark. I know the CDI works, but the exciter coil is too weak, so the spark is very hard to get. I measured the exciter and it's only 200ohms. it should be 320. ? and it show that the output is somewhere around 15volts, even the exciter should generate anything up from 30 to almost 200volts.

I could rewind the generator, but i'm too lazy:laugh so I was thinking about new hack mod. I noticed that the light generator is ok and that makes something like 12-16 volts. I have transformer that converts 220volts to 24 volts. so it's 10:1. My plan is to connect the transformer opposite to it's original way and use it to raise the lightcoil voltage to the cdi level. 12volts ->120V. and use that to drive the CDI.

so what is the verdict, am I going to kill my self with it or is it ok to do it like this?:coocoo

JarkkoT.
 

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Upside Down Super Mod,
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29,860 Posts
No sure it would work Jarkko,

Many many years ago I bought a non running RM125. It had compression and a great spark, but would not run. Someone had done some work to it and put the CDI coil 180 degrees out. The coil itself did the timing and it was getting spark at BDC instead of TDC.

Without looking it up, you're ligthing coil might have to output the same wave form as the old ignition coil. :dunno
 

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Upside Down Super Mod,
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29,860 Posts
Does the XR have a separate pulse coil to fire the CDI?
 
G

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Discussion Starter · #4 ·
yes, there it another little coil that determines the moment of spark. it's set to maximum ignition advance. the CDI box then delays the ignition from that to low revs.

sometimes CDI systems have diode at the CDI input(where the exciter coil connects). this prevents the charge from unloading even if the negative pulse comes from the generator before the spark is hit.

I think this cdi box doesn't have that. I may need to add that, then it would not matter what kind of loading it gets, as long as it gets it.

actually I found great CDI ignition page. http://www.transmic.net/gbindex.htm

there is actually DIY version on that web page that doesn't need exciter coil at all. it uses some multivibrator that generates the high voltage needed to load the CDI capasitor. I think this lightcoil + transformer is pretty close to that.

Funny thing about these CDI's is that they are shut down by grounding the ignition coil input input which can be 200 volts easily. so you actually have 200volts at your kill switch. so any moisture or dirt can make is stop or run poorly. And it's easy to get shock too.

TL doesn't use CDI(capasitor discharge ignition) it uses TCI(transistor something). difference is the voltage the coils are getting. TCI loads the coil with 12volts. CDI loads capasitor and releases it to small coil. CDI is more powerfull.

this brings out idea to TL. who is the first to build true CDI to TL :devious
 
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Discussion Starter · #5 ·
:) Installed the cristmas light transformer the wrong way and checked the spark. Good and strong. Damn I'm good.....:devious.

I checked that the light coil made something like 10volts at low kicking speed.(analogic meter), then I installed the transformer and it was making 50volts AC and that is meter value, so the peak value is way higher, maybe square root 2 times 50

I need to solder everything up and hide the transformer to airbox or somewhere and I can try to start be engine!

JarkkoT.
 

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Upside Down Super Mod,
Joined
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29,860 Posts
Good luck :thumbup
 
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Discussion Starter · #7 ·
This sounds like a bad thing. Hey ya'll watch this! Hold my beer. Hope it works for you and doesn't set the bike on fire.
 
G

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Discussion Starter · #8 ·
Trust me, I'm trained amateur and usually I know what I'm doing.

i know it sounds little wierd to use cristmas light transformer in XR500 ignition system :devious
 
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