The LT190, bought in 2005, worked very well and last year the engine started to cycle.
That is to say under no load condition, the engine starts without any problem and after a few minutes it suddenly looses speed as if was going to stall and then it picks up its speed again and continues to do this all the time. Changing the speed makes no difference.
I changed the air and petrol filters, adjusted the spark plugs, emptied the deposit in the caburator bottom cup, checked that the spark was present at each spark plugs, used fresh petrol...

Does anybody have any ideas ?

If it has a gov on it that's where I would be looking. You may have a broken spring it in.

Hi,
I would say it is in one or more of the low speed circuits. These are fed by the main jets, but are critical for high speed operation. Also possible is a weak fuel pump that "catches up" when the speed drops.
Peace,
Clarke