I got my jawa through necessity at first, I had got a job but no 
transport and only 250 pounds to my name. I bought the jawa (638350 twin) 
with 200miles on it as a non-runner (with sidecar initially, but that's 
another story) After two days of stripping carbs, fiddlingwith points etc. 
I finally noticed the plug caps were on the wrong way round.
 
 Three years, two write-offs (the bike and the audi that tried to 'u' turn 
in front of me) and 20,000 miles later I was on a run with the university 
bike club. We had gone from Edinburgh (Scotland)  around 250miles to the 
remote island of Mull on the west coast, a trip that entails two ferry 
journies and miles of empty, twisty, single track roads. We were heading 
to the ferry terminal on the island on the way home, fully laden with 
camping equipment and I was racing my mate on his Honda superdream. At 
around 85mph on the clock (I fiddled with the exhausts and carbs quite a 
bit), the engine lost power. Now I know what you're thinking... 'nipped up' 
but it wasn't like that and not like when it drops the spark from one 
cylinder, it was still pulling but not over 40mph.
 
 First call when the thing plays up is always to change the plugs but one 
of them had the electrode all smashed up. I whipped the cylinder head off 
to find a hole in one of the pistons. Now what? 
 
 The A.A. will take hours to get here if they come at all. 
I decided to just ride it with the plug out of the bad side and see how 
far I got.
 
 Going over Glencoe was interesting  (1:5 gradients with tight corners) where 
it wouldn't go over 10mph but I managed to cruise at around 30 all the way 
back to Edinburgh-a journey of 250 miles only stopping once for fuel. The 
bike club guys were expecting to pass me at the side of the road on their 
way back where someone would wait with me for a breakdown truck but they mucked
around so much I got back first and was waiting in the pub for them on my 
second pint of McEwans.
 
 Further investigation showed the small end to have collapsed allowing the 
piston to hit the plug. I cannot think that any Japanese bikes would have 
coped with this sort of abuse and still been in a fit state to be rebuilt 
(work in progress, just waiting for the barrels coming back from a rebore)
 
Scott Hodgson