my propane generator won't start

I have a champion 2500W duel fuel generator. I purchased it about 2 years ago. I bought this model so I could run it on propane. On our first trip, it worked well for a week or so. Then I had some difficulty starting it. By the end of our trip, it would not start at all. Since it was under warranty, I brought it to an authorized repair service. They said the cause was the intake filter was clogged, which they fixed. Next trip it started once, then hard starting, then it would not start at all. Again, I took it to be repaired. Same issue. Next trip it would not start even once. Now the generator is out of warranty. I could get it repaired at my own expense, but I am afraid the same problem to will happen. I need to find the root cause. Anyone have an answer?