If the 2500 has the same V-twin engine setup as the 3000 series. I just fixed my sister-in-laws. The air filter was soaked with fuel and the air filter housing had fuel/oil mixture in it. The air box drain under the carb air box was completely full of a gas/oil/blow-by mixture. From what I can tell, once it starts missing it runs down past the rings and raises the oil level besides diluting it. the crankcase vent system then draws in the fumes and they have too much fuel in them to ignite so perpetuate the problem. Check the oil level and if it is high, change the oil and filter with the correct grade for your weather and keep it mid scale rather than topped off. Check the air filer by removing it and with new/cleaned spark plugs and the air box cleaned up, see how it runs. the one I worked on ran just fine until I slid the filter back in the housing and it stalled out. Removed the filter and it started and ran OK again. Filter showed plenty of light through it but smelled like gasoline. Dropped in the new filter and it is still working great. Took a while and careful reading of the shop manual to find all the components that needed service. Also I was able to get it on my scissor auto lift (barely) so I could work underneath it standing up. Use the search feature for 3010 gas in oil and you should find lots of concerns, but few answers.