Hi Rcalzadilla,
Looking at your other posts, it looks to me that you might have the infamous valve seats coming loose. You've come to the right place and Quenton is the man who can get you fixed up as he has done for so many others here over the years. The only way to determine what the true problem is would be a tear down and inspection, but I'll leave it to Quenton and the other Whizzer pros to chime in.
If your bike is a 2003 model and everything is stock then most likely you have the WC engine which I believe was noted for having valve seats that work their way loose over a short period of time. If you haven't already, go back and check the previous posts on this engine and it's unique problems; Quenton has thoroughly documented these problems and his attempted cures.....I own a Whizzer NER which has it's own quirks....and have been corresponding with Quenton about alternative repairs. What you and I have in common is that the true fix-the NE5 cylinder and head-are no longer manufactured or available. A cast iron cylinder is available; I've been contemplating whether to go with the cast iron cylinder or try to have Quenton modify my existing NER cylinder. There is an item on Ebay listing an aluminum cylinder that looks like the NE5 cylinder. I'd advise you talk it over with Quenton should you think about going that route. As I've stated earlier, there is a wealth of info on this site regarding past issues for the new Whizzer motor. Good luck with your bike, welcome to the site and welcome to world of Whizzer! Let everyone know what the findings are!
Take Care,
Mike