jawa 207 ignition help

[mrw8]

[mrw8]

I asked this question of the parts dealer in Hungary and they it can all be wired separately even if it originally had a combined unit. But on closer examination the white wire on my moped is actually coming from where the yellow wire does on mopeds with separate Thyristor and coil so I need to put it on the I terminal of the thyristor and leave the 1 terminal empty. Then jump the 1 terminal of the coil to the I terminal of the thyristor and jump the 15 terminals together. There can only be two or three variation that will work or not so I'll find out soon.

[mrw8]

I have current from the generator and aux. circuit but have yet to get spark. I will attach the red to G. Then the white to I. Then the 1 to ground and also to the 1 on the HT coil. Then the 15 to 15 of the HT coil. that's about it.

I really wonder what stamp would tell me what model jawa this is.

and I'm still looking for a picture of the decompression cable plate that holds the cable housing.

[mountainmoped]

In my 13 years in the moped business I have only seen one Jawa. They are very rare in my area.

[John]

Anything on www.jawamoped.com

[mrw8]

lots of good tips on jawamoped.com. but this particular moped has lost most of the ignition components so it's a real archaeological project to figure out what goes where. I think I finally figured out how to wire the thyristor and the ht coil. it's got good compression and brakes and tires and everything but the ignition system was totally removed so I'm starting from scratch with what turns out to be a completely unique moped. I think it used the Tranzimo and I'm converting it to a Thyrsitor and coil but normally the conversion is to a combined coil/thyristor...so now it's going to be even more unique. I'm a little worried that I didn't change the stator ring to one with a white ground and a yellow impulse lead but with some work I think I can make it pop.

[mrw8]

I thought I would post my findings....but you can find the source material here:
http://www.jawamoped.com/JawaMoped_Elec ... nition.pdf

what I've learned is that these are basic ignition systems as long as everything is in place. If you have nothing to work with then you will have to learn what once belonged between the magneto and the spark plug....
and that will be an electronics history lesson..

There was originally something called a Tranzimo that timed and generated the high voltage spark. That must have been basic to wire because there are only two wires, current and impulse generator, going to the Tranzimo and one spark plug wire leaving it.

Other Jawas had a separate HT coil and a Thyristor which is some kind of inductive timing switch. It has 4 male pins...G, I, 1, 15
The alternating current comes from the top most coil on the magneto...it's usually a red wire. Behind the red wire is either a yellow wire or a white wire or a yellow AND a white wire. If it is only a white wire then that's called the impulse current line. The yellow wire is the impulse line also and the white wire behind the yellow wire is the ground...The impulse wire, regardless of color, goes to the I pin on the Thyristor. Maybe the I means Impulse.

But since the impulse current is timed to release the alternating current to the HT coil the current has to loop back around through the 1 pin. That is Ground. And that pin also is where the 1 terminal of the HT coil is jumped to. Then both the coil and the impulse current are both directed back to a ground that might be on the coil ring. I'm not sure on that because all kinds of variations exist. But I'm going to put it on the coil ring.

Then the 15 pin is the actual HT coil load and it goes to the 15 terminal on the HT coil where it is condensed to produce the spark on the plug.

thyristor pins:
G = alternating current line in/ red wire
I = Impulse generator circuit/ yellow or white wire
1 = Ground/ white wire AND 1 terminal from HT coil must be grounded on a coil ring screw
15 = load out/ HT coil/ whatever color you want.

The HT coil only has the #1 terminal that is jumped to the 1 pin on the thyristor and then back to the ground on the coil ring. I suppose these can take separate routes back to ground but the schematic shows them jumped together.
#15 terminal that comes from the 15 pin on the thyristor which is where the generated current is coming from at set intervals.
Also, the spark plug lead is a screw in type. I've read that the newer carbon fiber core spark plug wires are not recommended and my suspicion is that they don't mix well with the 1976 4 volt coil and 6 volt system of thyristors and a bicycle driven crank. It took some work for me to find a copper core spark plug wire but it came off an old Japanese HT coil...and I had to swap out the plug. But I trust it to work better on this moped.

That's my findings as of today and I'm hoping I can get spark when I put theory to practice.
I could be totally wrong but the schematics seem to suggest I'm in the ballpark.

[mrw8]

Indeed, today's tests were a success so this is the way to wire a thyristor and coil into a Jawa that initially had only a Tranzimo. I'd recommend getting a combined unit to simplify things since there is really no room to fit a coil and thyristor. I immediately fouled the spark plug or flooded the cylinder but I had spark and ignition and compression so I'm confident that this is how to wire it. It's probably been 15 years since that engine ran so this is a step in the right direction. They should make a show Czechoslovakian Restoration.

[mountainmoped]

Thyistors are designed to for high speed switching of large amounts of electric current. Their first use was in the precision timing of conventional explosive charges used to compress the radioactive materials in nuclear weapons order to initiate chain reactions. They are one of the banned items that were intercepted when a German company attempted to ship some to Iran. The Jawa peds are unique as they spanned the gap between breaker-point ignition and the CDI ignitions.

http://nuclearweaponarchive.org/Library/Pasley1.html

[mrw8]

that's a bit of history...

looks like the timing and spark are all working good...compression and clutches...etc...but I fouled the carb or plugged the idle port with gunk. not sure as it won't idle. I'm replacing the throttle slide so that might be it...or maybe the float needle isn't seating or the floats aren't level and it's overflowing...the carb bowl gasket I got from Hungary fits but is very thin. It's leaking from the bowl seam. I might make my own if it doesn't swell up. here's a video link...



and here's a picture of the cable housing decompression bracket. By a miracle the owner found it but now that I see it this is what I was going to make from scrap metal. you'll notice in the video I don't even need the decomp cable since it's starting pretty easily.

[mrw8]

[mountainmoped]

[mrw8]

it could be an air leak since the air intake gasket had to be fashioned from spare carb gasket material and right now I don't have any kind of air filter since the Jawa system is a crazy routing through the frame of the bike and into an aluminum piece. I also wonder if the transmission bearings have anything to do with it. without the clutch assembly installed then the rear wheel really shouldn't be spinning at all. So I think I need to pull the flywheel off to inspect the starting clutch area. Something is rubbing and causing the drum/wheel to turn even without the clutch installed. am I wrong? maybe a bearing is worn out...

I read the manual again and it reminded me to check the muffler for a clogged port. That's a good tip because the hole is very small. It could easily be clogged and regardless I should clean it out.

Air leaks,
clogged exhaust
carb needle
worn bearing

[mrw8]

the muffler needed a cleaning but that wasn't the problem. And I replaced the air intake gasket and then tested all the mating surfaces with some starting fluid and didn't get any fluctuations. I think my choice to rebuild the jikov carb was wasted effort. I've read nothing but bad reviews about the Jikov carb. Something is going wrong with the fuel delivery and I'm thinking the floats are sticking closed or the needle is getting stuck. I drove it around the block at top speed of 22 mph and the handling is atrocious...like a 1950 Norton mini cafe racer with warped rims. I'm glad it's not my moped.

So, replacing the carb would probably fix the fuel problem but a totally separate problem is the sticking transmission. I had the clutch pads off again today and there was almost no difference if the pads were on or off. (some of these diagrams call the outer pads the starting pads but my understanding is that these are the drive pads and the starting pads are behind the segment guide body. If I could still start the moped after taking the starting clutch pads off then that really would be a mystery. But translated Czech manuals are never wrong...so...)

The transmission was engaged no matter what so either the starting pads are rubbing against the clutch drum or a bearing is spinning in place or maybe the belt is caught up in some way. The flywheel is rubbing against the clutch drum in some way that I can't inspect.

I've used moped flywheel pullers before on my vespa ciao but looking at this clutch carrier assembly I can not see how a bolt can be used since the flywheel shaft is hollow but has threads. I screwed in a bolt but didn't like how it felt and and it didn't move the segment guide body assembly at all. The tool shown on ebay as flywheel removal for the Jawa in general is a bolt within a bolt but I don't think that will work for this 207 Jawa or not to remove the clutch carrier. The workshop manual shows a plate that fits the three small bolt holes and a center bolt that must fit into the hollow crankshaft and pull up and out. manufacturing something like this will take some work as I have to tap thick gauge steel to the size of a small long bolt and then drill the three holes to match the holes on the guide body. This looks like a special Czech tool for the 207 model and there is also something called a alternator rotor puller that looks more like the tool that will work but is designed for the other side...

Fig #10 is what I'm trying to do...and it comes before Fig #11 even though fig #11 is shown before fig #10.



does anyone want to buy a 1976 Jawa 207 Babetta with new tires, thyristor, coil, carb jets, throttle cable, clutch pads? recently serviced brakes, ignition, carb, lighting, chain, piston rings. Still needs more work. drives like a tank.