I have a 2008 Onan 5500 I just got the trailer used/as is from a reseller. When we looked at the trailer everything to be working and the generator was running. During our first trip we noticed a strong smell from the exhaust and at times running ruff. After the trip I went to service the system new oil filter and clean out the carb ect... I noticed the electric choke was disabled and the system was zip tied with the air valve on the intake about 95% closed. I took off the zip ties and and hooked the system back up and now the generator won’t stay running. If I hold the air valve almost closed it will run smooth but as soon as I let it open up it runs really ruff sputters and shuts down. I did a sea foam deep clean of the carb and replaced the fuel pump and filter and no change. Not sure what to do next new plugs maybe? Just need some help.