A 280E is a 123 chassis, and is fuel injected. Is this a carburated 280C? If it is, it may be the float in the Solex 4 bbl. carb. Mine went bad over time, and became harder and harder to start, would die sometimes, and load up (flood) at idle. I adjusted (lowered) the float level a few times, but that is only a temporary fix. Floats are available and relatively inexpensive, also quite simple to replace. Just be sure you adjust it to specs. Also, check the choke for proper operation before you go any farther in troubleshooting. The choke is primarily electric, and if unplugged or inoperative, the choke will not unchoke properly.