Man, if he has no strength and there is no obvious mechanical breakdown you have to think that combustion fails, either due to lack of air in the mixture and lack of fuel. You have to try and discard things, start with the air filter and continue back, fiber of dirty or plug folding that restricts the passage of gasoline when you ask for the most, in slopes or overtaking. If these two things are fine, you should think of dirt on the carburetor, stuck chiclés and/or dirty bucket, it is a matter of cleaning in general and, incidentally, a review of the spark plugs. It is very likely that if you do everything indicated you will have already solved the failure and if it was not yet fixed, because nothing writes again and we continue back.
Rafael's greeting