Cz 125cc two stroke.
This bike will only start if a vacuum cleaner is placed up the exhaust , turned on and then kick started.
I kid you not!
I think I must have a crankcase seal problem.
Problem started when my son didnt put enough oil in the two stroke mix, had a seize of the piston and this led to a strip down, knackered piston. Ordered a new one, turned up wrong size gudgeon pin 18mm not 16mm as required.
As a quick fix cleaned up old piston, fitted new rings from new piston. Big mistake, new rings were slightly larger , ring snapped old piston now badly grooved but cyl liner ok.
Ordered second piston fitted kicked for 2 days (no elec start) fails to fire , correct fuel mix , new plug ,,points, coil, carb cleaned several times, plug has fuel on it but wont bloody fire. I tried hoover up exhast to assist mix getting through and the bike fired and runs. I can turn off hoover when the engine is running but it won't start without hoover assistance..........any ideas or are the crancase seals the likely suspects..

I think a major rebuild is on the cards, parts are not expensive thou...
sling it over here and i will do it for you if you are not able to do it yourself, am only over the water

rio wrote:This bike will only start if a vacuum cleaner is placed up the exhaust

Can't help you with your problem, sorry, but I have to ask - what made you think of shoving the vac up it??

I was looking for a quick way of getting the piston out !.......but really I had tried everything I could think of...fuel, spark, compression timing etc, I was clutching at straws and thought maybe the mixture wasnt atomised enough to fire so the hoover seemed a quick method of drawing it in to the cylinder, but I still had to kick it over to get a spark.

My next plan is to try and locate any air leaks, some 2 stroke sites say block off air intake and exhaust ports and pump air under pressure down the plug hole, then squirt wd40 around joints and seals looking for bubbles !

Not sure that the Crank seals are the problem.
I had crank seals go on an MZ150 when I was a Sprog.
The symptoms were the bike would start and run fine but as soon as it warmed up it would gradually die.
Then it would not start again until it had cooled down.
Hope you get it sorted

Andy

i quick one here, i had a long time ago a non starter and i found a rubber pipe on the carb was misplaced, just needed to hang and not be joined both ends, just a quick thought

If the fault is not the crank seals im stumped. Its as if kicking it over doesnt draw in a good enough mix to fire but the assistance from mr hoover helps. Thebad starting only happened after the piston ring snap/jam so without a crank strip I cant see if the seals have been damaged by piston ring bits, new rings and piston are in and the liner seems fine. Anyone got a cheap 125cc cz 488.4 engine.........

I've run Jawa 350s before, a CZ250 twin and a couple of CZ singles. The 125/175 CZs did suffer from coking up quite a lot but back then most owners were using lawnmower 2 stroke oil so that wasn't a surprise.

Re: engine swap, I'd be tempted to get the ruler out and see if a Chinese CG clone motor would fit.

capitano wrote:Re: engine swap, I'd be tempted to get the ruler out and see if a Chinese CG clone motor would fit.

I was toying with the idea of putting a Benly motor in my Voskhod until Lyn very kindly fixed it for me