cz jawa any experts in da house

[Ferret]

I would say that you have a compression issue hence its not drawing fuel in and what does get in is not compressing . When we ran 2 strokes close to the limit when racing with excessive porting etc the only way they would draw in fuel and compress it enough was to bump start or tow . I would forget the Hoover as it's very dangerous to do and instead place a piece of card over the carb mouth and then try to kick it into life . When crank seals fail they usually allow oil from primary or gearbox to be drawn in and make it smoke like billyo .

[rio]

Regarding coking up, I started the bike with the kickstart with the downpipi off. It started but obviously sounded like a tank. I thought, what if the silencer is blocked. I removed it stripped dout the baffles, oily but not blocked . I reassembled it all and had a quick decoke anyway using the old gas bottle and compressed air method. Refitted to the bike and low and behold it still wont start.
I fired it up with hoover assistance and while running on axle stands went up the gears no prob to 50mph. At tickover I squirted wd 40 around all joints, crancase, cyl head, cyl base inlet from carb etc but no air bubbles or fluid being drawn in. I could still have crankcase seal probs but I am trying everything else I can think of before the big engine out/crankcase split........

[rio]

Update...went in deep, engine out stripped right down, split the crankcase.
The section where the crank spins had a fair bit of oil from the gearbox. I thought this section should only have the fuel /oil mix in so either its getting in from the clutch end or past the gasket. Maybe it wont fire due to the oil mixing with the fuel mix !
I will source some seals and fit a new gasket and offer a sacrifice to the cz gods and hopefully I might get a hooverless start.......dont hold your breath......

[rio]

Deflated.............new crank seals new rings, top roller and gasket kit,
Reassembled and tried to start ....no
What a croc ! Good compression, good spark, fuel getting to plug
Starts eventually with hoover, very erratic tickover, gets lovely and hot, turn off, try to restart kick and kick...nothing
Talk about light at the end of the tunnel, I cant even see the tunnel
Just about out of ideas any cheap 125cc cz engines out there

[Ferret]

Ok firstly have you tried just putting a small amount of fresh fuel straight down the plug hole and trying to start? ,if it does without the assistance of your Hoover then try a piece of card over the back of the carb and try kicking over again . If it starts you may well have air leaks at the carb or mounting points As this all points to not drawing fuel in correctly as in too lean . If it's back firing then I would suggest re checking the points and condenser . I presume you put a new plug in it aswell as they do fail under load more often than we may think .

[rio]

Thanks for feedback, away from home for a few days with work ,
so will try your ideas this weekend and post results

[rio]

Spoonful of fuel in plughole , kicked over , bike tried to run.
I took off bellow ,held card across carb intake and kicked again. It didnt start and cardboard
coated in fuel. While the bellow was off I could get it to run if kicked while the throttle was held fully open .It ran while I blipped the throttle but wouldnt tick over even with the idle screw fully in. At least it starts without the hoover now so its carb off again and further investigation

[Ferret]

Ok fuel on card is good ,failing to start could just be over choked not a problem . There does appear a problem with either with partially blocked main jet and or emulsification tube or it could be wear on the needle . Having to hold it full open to start it suggests that the slow running circuit or pilot jet may also have a blockage . I would strip the carb out completely and rebuild ,then see where you are at .

[rio]

Latest....stripped carb , blew out all airways , inspected everything , all seems fine , size 80 main jet size 50 air jet. Reassembled and refitted. Primed system, a few kicks and it tried to start. After a bit of fiddling I could get it to run but wont tickover. I had to turn the air screw in fully (not 1 turn out)and turn tickover right up to get it to run .
A few days ago I took off carb and exhaust, sealed holes , put a tube in the plughole and using a footpump pressurised the crankcase . It held at 7 psi while I sprayed soapy water on any joints. All ok so no obvious air leaks.

Considering its a basic 2 stroke that can be repaired by an old farmers wife in a field in a snowstorm it seems to think its a delicate italian bike that has to be coaxed and mollycoddled to even reward me with an occasional start......bugger

[Ferret]

The fact you have to cut all the air out of the system to get it to run suggests that there is either still a blockage in the carb on the fuel side or it is sucking in too much air via a leak . You did not say if it has a choke on the carb and weather you have to have it on to keep it running ? Does it rev once running ?