I purchased a new Cub Cadet Challenger MX550 on 05/01/2021. The UTV had approximately 4 hours on it from dealership at purchase. Completed a few hours of break in riding then went out of town for a vacation that involved trail riding with UTV on 05-10-2021. First day on vacation the UTV started missing and bogging down then quit running and would not crank. This occurred at 7 hours. I check the oil prior to every ride and upon inspection of the oil level it had climbed above full and smelled of gas. I checked air filter and found oil in the breather box and on the air filter. I called several Cub Cadet warranty repair dealers and they where 4 to 6 weeks out for repair work and recommended carrying the UTV back to the dealer I purchased it from. We had scheduled to stay thru 05-29-2021 and the UTV sat on the trailer until we returned home. I contacted the local dealer and dropped off UTV for service advising them of what had occurred. On 06/04/2021 I spoke with dealer and was advised that the spark plug was fouled and the fuel injector was not working properly that they had ordered parts to make the repairs. On 06/08/2021 I was called and told that repairs had been made but they where testing the UTV to assure it was repaired. On 06/17/2021 I stopped at dealer to check on progress. I was told that the UTV was ready to go. When I returned with trailer to pick up the UTV it would not crank and the technician took the NGK spark plug out and it was covered in black soot and fouled. The technician went in and called Cub Cadet/MTD warranty on speaker phone while I was there. (Cub Cadet case # [protected]) we spoke to Cooper. The technician at dealer explained that he had completed the replacement of the fuel injector, spark plug, changed the oil and air filter. That he had tested the fuel pressure and completed all recommended test procedures that Cub Cadet warranty specified and the UTV had fouled the new spark plug. Cooper then asked if anyone had spoke to the customer to see how it was being used that the UTV was not designed to be stopped and started frequently and they would foul spark plugs. I spoke up and introduced myself and explained the story as described. I asked Cooper why a new UTV that has 7 hours was fouling spark plugs so quickly. That it had fouled a spark plug at the dealership during their testing that I had not picked it up since being repaired. I also asked why a fuel injected computer controlled air induction system and fuel system was fouling sparkplugs. He stated that other things like oxygen sensors and mass air flow sensors are part of the system and need to be checked. I then asked why we did not see a check engine light come on if those sensors are part of the system. The technician then told Cooper that the UTV had been fouling spark plugs since they had it and he had probably replaced four spark plugs in the UTV. I again stated that the UTV is new with 7 hours and I wanted my money back since no one could tell me why it fouls spark plugs so quickly. I have had other ATV's and small engine mowers etc... They very rarely foul spark plugs and only need to be replaced at the yearly service. I asked for a call back from a supervisor at Cub Cadet. We ended the call with Cooper. I left the dealer repair center and went to the sales center and spoke with the manager Patrick. Taylors Auto Sales/Cub Cadet of Wilmington NC. I asked Patrick to call Cub Cadet and lets speak with someone about returning the faulty ATV for a refund. He acted like he did not care that I was having problems and told me I would need to call Cub Cadet and maybe if I complained enough that something would be done. I felt like he was refusing to help me and asked to speak with the owner. He simply stated he would let him know and that they would need to get a code reader to work on the UTV. I simply stated that the check engine light was not activated so there are no codes. I called Cub Cadet/MDT customer service and spoke to Scott. I asked for his last name and he told me it was company policy not to provide the last name. I explained the situation and told him the UTV is brand new, should not be fouling spark plugs and I wanted to return the UTV for a refund. He told me the dealer had to initiate the refund. I explained that Patrick the Manger of the dealership referred me to customer service and refused to assist me. That I need to speak with someone that could assist me because I was not getting any answers or assistance. He was very curt and what I considered obnoxious and referred me back to the dealer. He refused to forward me to a supervisor. 06/17/2021 345pm received a telephone call from Dustin Warranty Supervisor. He assured me the UTV would be warranty covered and that notes where in the file and if I had future issues it would be covered. I asked him why a new UTV with 7 hours is fouling spark plugs and he explained the stop and start issue with me but had no mechanical explanation of why the UTV was fouling sparkplugs so quickly. I again stated that it was a brand new UTV and wanted a refund of my purchase price. He stated that I would need to discuss that with the dealer. I explained my earlier conversations. He tried to help me but really could not answer my simple question of why a UTV with 7 hrs is fouling spark plugs, has oil blow-by in the air filter and is getting gasoline in the oil. He simply stated that it was a good idea to have extra spark plugs to replace them so I would not get stranded again if I broke down. I called the dealer repair center and asked to speak with the owner of Taylors Auto Sales/Cub Cadet Wilmington and spoke to Andy. He stated that he was aware of the mechanical issues of the UTV and I explained everything as stated above. He told me he had gotten a code checker and was going to work on the UTV when he could. I explained that it was brand new and should not be fouling spark plugs so frequently. That I was requesting to return the UTV for a refund. That it was going to be a continuous problem. That the fuel injector going bad I understood but the spark plug fouling after that was repaired did not make logical mechanical sense when everything tests within specifications. He agreed with me and stated that he did not agree with the answer Cub Cadet provided about carrying around extra spark plugs. That he would check on the refund process for me. That my customer satisfaction was important to him personally as a Cub Cadet dealer. 06/21/2021 Andy called me and stated that he personally worked on UTV and found that an Autolite spark plug was installed in the UTV. That the UTV should have a NGK plug installed. That he had gone up one heat range higher on the NGK spark plug and that he did not find any codes in the computer. I advised him that I was present when the technician took the new plug out of the UTV and it was a NGK plug that was fouled when I tried to pick the UTV up when I was told it was repaired and ready to go. That I was not there when the plug was installed back in the UTV by the technician. I again stated that I wanted to return the UTV for a refund because it was brand new and should not have the related problems that I have experienced. He stated he would check into the refund and let me know. I read the owners manual of the UTV and there is no mention of sparkplug fouling and inspection in the manual. I did not find any reference to sparkplugs in the manual or a part number for replacement spark plugs. I did find the recommended NGK spark plug number which is a genuine Cub Cadet replacement part on-line. So why a warranty repair dealer would install a Autolite plug replacement in the UTV does not make sense. There is no mention of short term operation causing running issues and I was never instructed of these problems when I was considering a purchase. Cub Cadet has a quality name with their outdoor equipment and I expected reliability and quality customer service from the product and purchase experience.