not a cossie problem but on a N/A 4cyl mini engine, bizarre till we worked it out anyway.

with distributor / coil ignition, starts running on 3 cylinders (felt like a plug lead had fallen off). to try and indentify the faulty cylinder (or plug) we take each lead off in turn.

the engine is idling at the time.

removing #1 causes the engine to slow till almost stalled.
removing #2 increases engine speed.
removing #3 has no effect on engine speed.
removing #4 has no effect on engine speed.

answer later.....

 

no too difficult really - the fact that you were removeing the plug lead has the effect of creating a 'supercharged' spark to the plug , hence the uplift of revs

 

 

give us a clue, what's the firing order?

 

1342, its only a mini engine!

there is a siamised inlet port between 1 and 2. 3 and 4 have thier own inlet port as well. 2 and 3 share an exhaust port, whilst 1 and 4 have thier own individual ex ports.

"the ex valve had seized in the guide resulting in the valve hitting the piston and destroying the engine"

 

I would have guessed sticking/bent valve lol

not good thou