Jawa x30, very weak spark

mark voznyuk /

Jun 21, 2020 06:49PM

Hi there! Recently got this 1981 jawa x30 (207? 210? Something) for pretty cheap.

Freed up the motor and discovered that it has pretty weak spark (you can see it but its razor thin, and you have to spin up the motor pretty fast to get anything)

And knowing jawas, it has a very complicated ignition, and im not sure where to start, changed the plug, same thing. Guessing it's the coil or the thryster. As the alternator works for the headlights (this is the one with the black 4 wire box and the silver cylinder coil)

Any input on where to get parts as well? Only thing on treatland is tires.

Thanks again!

Re: Jawa x30, very weak spark

mark voznyuk /

markopollo

Jun 21, 2020 07:20PM

Heres a better picture of the ignition system, the coils do have surface rust on them, but the headlight works just fine, so im ruling out the alternator as the main problem (edited)

Re: Jawa x30, very weak spark

Pushrod Fifty /

supercub

Jun 21, 2020 08:09PM

I would start by cleaning every electrical connection and making sure they make firm contact, clean that rusty mess with electrical contact spray. Replace the plug wire and cap.

Re: Jawa x30, very weak spark

mark voznyuk /

markopollo

Jun 21, 2020 08:22PM

Well, also, i tested the thyistor and the coil today.

160ohms for the thystier between the 1 and l

And 1 ohm for the coil, seems to be within spec

Guessing its going to be a bad connection somewhere

Re: Jawa x30, very weak spark

Frank Bailey /

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themechanic

Jun 21, 2020 09:40PM

It's always the thyristor. Trust me, build one or buy one. Just do it.

Re: Jawa x30, very weak spark

mark voznyuk /

markopollo

Jun 21, 2020 09:59PM

im hoping to build one in the future, but i replaced the coil wire and cleaned the grounds back up, were back in business!!

clean spark, now to address the second issue, 45psi of compression....

Re: Jawa x30, very weak spark

Frank Bailey /

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themechanic

Jun 21, 2020 10:08PM

The capacitor component of the thyristors like most don't age well. If it works, my experience has been you get a miss at speed. Hopefully your low compression is simply stuck rings. Good luck, make it go!

Re: Jawa x30, very weak spark

mark voznyuk /

markopollo

Jun 21, 2020 10:18PM

thank you

im hoping to get it running and just to ride around for fun.

im guessing the rings haven't moved in 10 or so years!

woundering if the compression release has had it

Re: Jawa x30, very weak spark

P D /

pdcomm

Jun 22, 2020 07:52AM

Guess you'll find that out when you pull the top end .

Then , lap the decompression valve into the seat , so it won't be a problem .

Re: Jawa x30, very weak spark

Born to be WillD /

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willd

Jun 23, 2020 01:21AM

this page has some details on testing the thyristor:

https://www.mopedarmy.com/forums/read.php?6,1834014,1834512,flat=1#msg-1834512

and a great verview PDF here: http://www.jawamoped.com/JawaMoped_Electrics_-_ignition.pdf - if nothing else read this one.

and common issues here: https://www.mopedarmy.com/wiki/Jawa_ignition_testing

the DIY instructions to build one are here:

https://www.mopedarmy.com/wiki/Jawa_Thyristor

I have done that twice and it goes from a weak little zap to fucking inch long lightning bolts.

Glad it works but theyre notoriously problematic and I still support Franks suggestion of replacing it when you can. Do read that PDF if nothing else.

Re: Jawa x30, very weak spark

mark voznyuk /

markopollo

Jun 23, 2020 04:13PM

> Born to be WillD Wrote:

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

> this page has some details on testing the thyristor:

>

> https://www.mopedarmy.com/forums/read.php?6,1834014,1834512,flat=1#msg-1834512

>

> and a great verview PDF here:

> http://www.jawamoped.com/JawaMoped_Electrics_-_ignition.pdf - if nothing

> else read this one.

>

> and common issues here:

> https://www.mopedarmy.com/wiki/Jawa_ignition_testing

>

> the DIY instructions to build one are here:

>

> https://www.mopedarmy.com/wiki/Jawa_Thyristor

>

> I have done that twice and it goes from a weak little zap to fucking

> inch long lightning bolts.

>

> Glad it works but theyre notoriously problematic and I still support

> Franks suggestion of replacing it when you can. Do read that PDF if

> nothing else.

yup, anyone know the specs on what thyristor to get? as i clicked the link but nothing, as id like to know before the original box kicks the dust.

and the bottom ring had a hairline crack and broke in my hands, ordered new rings off treatland, hopefully it should run!

Re: Jawa x30, very weak spark

Leo Heyman /

leoheyman

Jun 23, 2020 11:06PM

hone that cylinder when you put new rings in

check the end gap

wire wheel that rusty ignition rotor too.

its a 207 engine.

reliable as a stone except for the ignition

buy an extra thyrister as a spare

red-yellow-white-blue.....wire sequence

i had a maroon 207 and ran it hard all summer long

it would only go 29mph but i loved it

Combloc styling

Re: Jawa x30, very weak spark

mark voznyuk /

markopollo

Jun 29, 2020 06:28PM

Just like Kyle #1

IM BAACK!

So, got the rings in and it puttered puttered ran then died (assuming the thysistor box last hurah!)

Now.

I would like to build the diy one, can someone link me the 3 pin thysistor they used in the picture? As the link isnt leading to anything and im not familiar with thysistors.

Re: Jawa x30, very weak spark

Steven Davis /

neflfixitdude

Feb 19, 2021 01:05PM

I'd like to bump the last post by Mark. Come on, someone out there has to have more info on building a thyristor since the Wiki images have disappeared...

Re: Jawa x30, very weak spark

mark voznyuk /

markopollo

Feb 19, 2021 01:13PM

here are some images I found on it, seems straight forward enough (i was lazy and order a new one, wish i never sold that bike)

Re: Jawa x30, very weak spark

Brian F /

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brianf

Feb 19, 2021 04:54PM

Wiki images should be back once the wiki update is done; Simon's working on it.

The Jawa ignition is no more complicated than any other CDI. I personally think it's much simpler than the typical CDI, as the magical black box is a super simple, well understood circuit.

A thyristor is a readily available part often used in power electronics, typically constructed in either a PNPN stack or as a cross-coupled NPN and PNP BJTs. Think of it like a transistor that latches on when triggered.

It looks like the thyristor used in the circuit on the moped wiki is an On Semiconductor MCR106-6G; they linked to Newark, who doesn't appear to sell them anymore (always use the manufacturer's part number, not a distributor catalog number, folks!). Should run you about $0.60 from digikey or mouser. (edited)

Re: Jawa x30, very weak spark

Brian F /

Go to branch

brianf

Feb 19, 2021 04:58PM

> Frank Bailey Wrote:

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

> It's always the thyristor. Trust me, build one or buy one. Just do it.

The Jawa I'm working on (sold as no spark) had a bad spark plug boot. The thyristor tests OK, we'll see if it works.

Re: Jawa x30, very weak spark

Steven Davis /

neflfixitdude

Feb 19, 2021 10:30PM

Thanks, man!

Re: Jawa x30, very weak spark

Brian F /

Go to branch

brianf

Feb 20, 2021 01:42AM

No problem. I'm not certain that this is the best possible choice, but it has worked for other folks so it's certainly worth trying it out. Looks like a pretty robust little guy.

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