Variations in Mitsubishi Motor 4G 64

Hello, I am having variation problems with this engine. When I accelerate thoroughly and keep it accelerated without lifting the foot of the accelerator, the engine begins to have variations of revolutions, they upload and lower each approx 2 second. Something like that happened to him? Where can the problem come from? Thank you very much greetings to all, awaits some answer.

The engine is carbonated or injected if it is carburado can have problems of air or carburetor inputs itself since some come with a plastic or vaquelita body.

Compa If the engine is in injectors it happens that it brings electronic system that does not allow the engine to be strangled while this stand up 2500 or 3000 and falls is normal in the Nissan

The engine is Naftero and LPG. Has LPG carburetor impo model 60. We have already changed the diaphragm and full cleaning. What we try is to give it more or less air entry and the result is that it runs out of force.