Same thing happened to me! Just got a new carb put in a year ago by Cummins while we were wintering in Florida. They replaced it with the new updated (California specs) 146-0663. ๐ On our first summer non-electrical family get together, the gen ran about 20 seconds and then died. The fuel pump seemed like the probable culprit, so when I got home, I ran the pump; and it was not only working, but running back out of the air intake!!
So . . I figured that since all of the adjustments on the 146-0663 are sealed, I figured that would also apply to the main jet/fuel; and especially after my first half-hearted attempt to pop the plastic thingy off of the bowl.
So . . . I figured I was stuck with buying another carb, and called Cummins Canada to set up a service visit. Wow! Totally different than Cummins in Forida!! And in a very bad way. They don't have time nor inclination to to service rinky dink RV stuff; nor do they even carry the parts! Not only that, but they couldn't provide useful information as to where I could get it repaired. So I called Hitch House in Barrie, Ontario; and told them I wanted to arrange a service appointment to get my carburetor replaced. At the outset, they tell me:
1. 2 hours labour charge to diagnose the problem!! There was nothing to diagnose! . . . I just want my carburetor replaced!!:R
2. They don't carry the standard Onan carb which fits every Onan for the past 15 years, in stock. :R
3. So . . . now to order the carb. The parts department checks the cost of a new carb, and exclaims: Wow! That can't be right!! :? $474!! Let me call Cummins (Ontario) and verify that! Fifteen minutes later, I get call back. Nope! A new carb is NOT $474!! It is actually $596.00 !!!! Not only that, but there is only one 146-0663 carb available in all of Canada!!:R
Well . . . goody for Cummins Canada. Just hope that if your Onan fails, it doesn't happen in Canada!
Anyway, this whole effort significantly inspired me to take another look at my 146-0663 carb. And I learned:
1. With nothing to lose, In got a big honkin' screw driver, and the altitude thingy popped off, allowing bowl removal just like to good ole' carbs.
2. Sure enough, just as OP j-d said, the plastic float had swollen (or whatever) causing the float to bind.
3. Enough for one day. When I start doing stooopid things, it's time to shut down for the day. Tommorow, I am going to shave down the sides of the plastic float fulcrum, with reasonable expectation that this $900 problem will no longer be a problem. ๐
UPDATE: I successfully finished the operation today, and everything is running great again. I sanded off about .07" off of each side of the float fulcrum, and that's all that was needed for free operation of the float. I also scraped a bit off of the arms just above the fulcrum to make sure that wouldn't get snagged as well.
