CZ 125 won't start all of a sudden

[jacksonaron]

Hi all!

First of all thank you for the add.


My name is Aron and I bought a 1985 cz 125 this past fall and I managed to get it running and did a few laps on it around the block a couple of weeks ago.

It didn't react that well to the throtel imput and wasn't very strong so I played a bit with the air and idle screws on the carb. After that I managed to start it and ride again a few times until a week ago when it started than boged down and never started again

I tried it today and it started but died right after like 2 seconds...

I have cleaned the carb, I have a new spark plug that they told me is for this bike, there is spark, it seems to have compression, but I dont have a tester...


It backfired once on the carb after not starting.

I can't figure out what to do next. Can anyone please help me?

Thank you in advance.

Aron

[Taught2BCauti...]

I think your bike has a contact-breaker type ignition, so check that the points are set to the correct gap, the condenser is good, and that the timing is correct.

If the points look pitted and worn, fit a new set and a new condenser.
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Honda Varadero XL125(V8)
www.TheFutureIsHere.eu

[RhynoCZ]

Toss the ignition into the bin and buy yourself a 12v contactless ignition from VAPE.

There are also other manufacturers of the contactless ignition system, but VAPE is the only one I can think of right now. You could also fit ignition from a Babetta moped, that you'll get battery less ignition system.

VAPE: https://www.jawamarkt.cz/en/electric-2/electr-ignition-set-12volt-top-price-

By the way, that site is one of the few sites, where you can buy every single part, made in CZE, for your Jawa or CZ, prices are very low, the quality is very high actually. Everytime I check these sites I wonder why am I even riding a Japanese bike, where the chain, for example, costs 5 times more and a lot of parts you can't even buy brand new for a Japanese bike.

Thanks mate, I'm back in the, let's buy a CZ mood.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[stinkwheel]

Check the terminals on the coil are making good contact.

Check the plug cap is making good contact.

Be aware of the difference between "a spark" and "a good spark". The latter is fat, yellow/blue in colour and arcs between the centre of the plug electrode and the tang, not off to one side.

First thing to do is changes the plug.

Second thing to do is put the carb screws back to the factory settings.

Third thing to do (if it still wont start) is to clean out the carb and check fuel is running from the fuel tap.

If it has been sat unused for a long time, there will likely be quite a lot of "varnish" inside the carb. If it has been sat for a very long time, there is also a good chance the crank seals are shot. You would tend to find it'll start eventually on a bump start if this is the case. Try putting your hand over the end of the carb to check for a vacuum through it when the bike is kicked over, it should suck your hand against the end of the carb. Classic symptom of shot crank seals is good compression but no vacuum through the carb.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jacksonaron]

Thanks for all the replys. I'll look into the 12V ignition system, I heard it is possible to use a Trabants ignition on a CZ (there are a lot of unused trabis where I live).


Anyway, I checked the vacuum on the carb and I felt some suction but not very strong. I alos noticed when I removed the rubber connecting the filter with the carb, that there is gas in it after only a few kicks. I think the gas is coming through the two little holes inside the carb (near the intake end of it), is that normal?

Thanks again for all the tips. I'll check everything mentioned as soon as I'm finished with exams...

[jacksonaron]

Hi,

So today I tried starting the cz again with no luck. Although when putting starting fluid in the carb at the air intake it did rumble and sounded like it was OK, but then I guess the fluid ran out and it stopped. It's not doing anything with gasoline. I don't think it there's no vacuum, because the spark plug gets 'wet' after a couple of kicks.

I also noticed it is spitting gas when kicked out of that little hole I on the carb intake side.(right hand side hole on the pic in the link)

https://thumbs.ebaystatic.com/d/l225/m/mHqzx-Wl_FGbebnWQpgo97w.jpg

Any further help would be appreciated.

[pepperami]

Ok, so you have sparks and compression?

So are you getting to much air or to much fuel? or not enough?


Wet plug can be a sign of to much air preventing ignition? possibly?
Fuel being where it is not supposed to be could? possibly? maybe? be an indicator of a stuck float?ie fuel pissing out.
The worlds smallest piece of grit can prevent the float needle from closing.

However when I owned CZ`s the most common reason my bikes would not start was because the points had shifted/closed up/got a bit of carbon in them.
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I am the sum total of my own existence, what went before makes me who I am now!

[jacksonaron]

I don't think it's the points, because it had ran at one point and than just quit the next day and never start again... I did clean the carb to.

I was thinking maybe the timing is off but would that explain the behaviour that I described?

Or is it possible that if there's too little vacuum at the intake, and the fuel doesn't get vaporated properly and it just flows into the chamber?


Anyway. Thank you for all the help so far.

[pepperami]

[jacksonaron]

hi,

I just wanted to share what the solution was to my problem if anyone encounters similar simptoms. All I had to do was to put in a new plug and plug cable... (the plug that was in the engine was new as well so I don't know wh it didn't work, but with the newer one its ok.)

Now my bike starts like a dream. I just have to find a way to get it road worthy lol.

[RhynoCZ]

Maybe the plug was wrong. A feeler gauge should tell you if it was it.
____________________
'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[stinkwheel]

Duff plugs are pretty common. A new plug not working is not that unusual which is why it's important to actually look at the spark and see if it's a good-un if you're having problems. "It's a new plug" doesn't mean it's a working one.

I like to keep the old, known-to-work plug(s) I changed at a routine service kicking about somewhere for fault finding purposes.

I've heard of some batches of new plugs rocking worse than 20% defective.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.