Hacking: CZ250 Sport

I read about mine in a small ad on the wall of the local DIY store. I rang the number six times over two days before it was answered. A young woman tried her best to tell me all she knew about the bike, but explained that the owner was on shifts and rarely available. In fact, no possible time at all was convenient to see the owner.

Hitching up my trailer, made from a Reliant back axle and a single bed frame, to the van we made off for the address. Lo and behold, there wasn’t anyone in. Sneaking around the back garden, the bike was soon found. Apart from rusty and slightly peeling chrome, the tank and seat were loose, due to loose or missing nuts and bolts. It was fairly tatty, but what other five year old bike would be advertised for thirty five quid?

Just as we were leaving, a portly blonde came rather quickly out of a house a few doors down, wanting to know what we were doing. Half an hour later, after a bit of haggling, she finally let us ‘rob’ her of the machine for £25. Getting it onto the trailer was a bit of struggle as there was no tail-gate and it was very high off the ground.

I’d tried for a while to get the CZ going in the last owner’s garden without success (the key had been left in the ignition). Once back in the comfort of my garage, I charged the battery, washed out the carb and tank - which made no difference. Taking out both sets of points, I cleaned them up; together with a new set of plugs, at least produced a spark. Still no joy.

The mileage was only 5000 - I began to wonder if the baffles were all gunged up by the fairly basic, oil mixed with petrol, lubrication system. I had a healthy spark, fair compression, petrol coming through to the plugs, so what could be wrong? The kickstart and gearchange share the same lever, it only took me a few kicks to discover the folly of this quaint idea, as the lever constantly slipped from under my boot, flying forward, putting the bike into gear.

The baffles weren’t very dirty, cleaning made no difference. New condensers, different secondhand coils, plug leads and caps, petrol into plug holes, all and more were tried in vain. I’m rarely beaten and refused to lift the head, feeling the trouble lay elsewhere. I was checking the compression again one day, with my thumb over a plug hole, having left the ignition on by mistake, when the spark looked like it didn’t appear at the right time, occurring somewhere near the bottom of the stroke.

Thinking (or hoping) it was a simple case of having he plug leads swapped around, I wasn’t very surprised when it made no difference. Putting a pencil down a plug hole and an ohm meter across the points, I was amazed to find they would only open just after TDC, or if the low tension connections were swapped just before BDC.

Moving the backing plate holding the points, as far as it would go in each direction didn’t give anywhere near enough movement to make any noticeable difference. The only thing to do was to open up the points or file slots in the back plate (which was impossible). Using the depth gauge on my vernier caliper, I got one cylinder at the right firing time. I had to open up the points to FIFTY FIVE thou before I could put the back plate back in the central position.

I quickly threw all the bits back together, ready to test this apparently ludicrous set up. These bikes have no choke, just a tickler, like a lawn mower engine. Suitably primed and tickled, I got ready for whatever might possibly happen. Nothing for a few kicks, then a blow back through the carb which reminded me to put back the filter and intake hose. After experimenting with different throttle openings, it fired up - a low sort of choked mumbling issued forth at a very poor rate of knots until the tickler was judiciously used in conjunction with the throttle. I guessed that I might have flooded the crankcase, but the bike lacked the drain plug fitted to my old BSA D7 Bantam, so I couldn’t check that.

Dense clouds of blue smoke finally cleared us she started to gain momentum and chug quite fast if the vibration was anything to go by. Warming it up, I revved the engine to help clear out any more smoke; to my amazement it just kept coming. Revving it harder, the vibration made the machine hove a foot to the right, almost tipping her as it ran out of concrete under the stand, with the lawn looming up.

The points were spitting out yellow sparks, which made me decide on a new set, although I couldn’t understand why the new condensers hadn’t dealt with that. I put on a few other bits and stuck some tools in my pocket, to take the bike for a ride.
I did expect a bit more than fifty five. After buying some new gaskets I took off the head. I didn’t find much wrong until de-coking one of the piston heads - bits of piston ring were embedded in it...

I bought a Haynes manual which enabled me to adjust the carb properly, set the plug gaps, etc. Pumping up the tyres, adjusting chain and throttle cable, etc., did help the heap up to almost 65mph. Going against the manual, I put in a 32:1 petroil mix instead of the 25:1 which cut down the smoke a bit, although it seemed noisier, hotter and occasionally felt as if it was on the verge of tightening up.

Soon after, it constantly went on to one cylinder. Thinking I’d made the same balls up as the previous owner, I bought gaskets and two new sets of rings (commendably cheap), hoping I’d get away with the same pistons. All was OK except for one piston looking as if the engine was running on the weak side, but the new rings went in anyway. Thrashing in the new rings to get them to fit the bore as soon as possible didn’t seem to harm the engine if you can call five grand thrashing.

I was never able to extract any sensible information from my local dealer regarding the massive points _ gap - but he was quite happy to take the bike in for an afternoon at ten quid an hour to sort out the problem: no chance. It usually took about twenty kicks to start when warm or after a run, double that at least when cold. I had my suspicions about the problem, but it was only when I read in the UMG that the ignition switch was dodgy and caused lots of problems that I found a solution to the erratic nature of the CZ.

I sold the bike to my long suffering brother who carried on using the CZ until the weaker oil mix led to the seizure of one of the pistons. A rebore and new piston were added but rather than improving the performance it left it much as before. He bought another CZ, the masochist, and used some of the 250’s parts in his 125, after the former bike’s MOT and tax ran out. The 125 is just as fast (or slow) as the 250, although it is a little newer and better looked after.

If CZ fitted decent electrics and they’ve been well looked after, then they would make a viable proposition as a sensible plodder. I’ve owned BSA Bantams and the truly pathetic Wipac switch gear used on these bikes is certainly no worse than the CZ's. I have not seen a late CZ, but if notice isn’t taken of genuine criticisms of inferior designed and made rubbish, then the CZ. will deserve to go the same way as both the Bantam and the Dodo.

David Dale