You can have your valve clearnaces done the day before and it still go bang.Andy_Edw wrote:But it had a valve clearances not long ago,And it wasn't ticking its head off before it went
Just the same as you can get an all clear from a medical check and then die a week later from heart attack.
5 months is quite a long time for something else to happen.
There are 2 coils... they both fire 2 cylinders each so if you have 3 plugs working then both coils are working so the Ignition box should be fine.
It's more a problem like arsey30 said with the cylinder / carb / plug.
You need fuel / air / compression / ignition for it to run.
This means the carb needs to be setup
The valves need to open / close properly and at the right time and the piston needs to have a good seal to build up suction and compression.
If it was running fine on all 4 then suddenly dropped to 3 and went with a big bang it sounds like the cylinder stopped firining but carried on sucking fuel in and then it built up in the exhaust and burnt.
I don't like sudden failures.. it is usually a sign of mechanical damage.
Check that nothing has come loose, if you can get in there crack the plug and shine a torch down the bore and see if you can see anything.
A compression tester is a quick easy way to check the cylinder and valves are within the same spec as the others.. if the cylinder tests out ok then you can thing about carbs and plug / plug lead as that is all it can really be!
Shouldn't take too long to diagnose / fix if you look in the right places
