Recently tri ed starting my Laguna Seca after a layoff and gas poured out of the velocity stack. Decide d a 30 year old bike needed new float valves. The new ones were different in that they incorrporated a spring unlike the originals. Installed a set in the rear carb and the bike wouldn’t run although the gas stopped flowing and the float bowl had gas. Sprayed a little starter fluid in the rear carb and it ran for a couple of seconds. The front carb didn’t,t run at all. Installed the new valves in the front and still didn’t,t run. The float bowl was dry..Removed the gasket at the bottom of the seat which I mistakenly installed and the float bowl filled and the bike started on the front cylinder alone. The rear carb has gas in the float bowl filled, new spark plugs and clean jets. Still think it may have something to do with the new float valves.

Silly question did you replace the seat as well as the needle?
If they were leaking fuel you may want to also take a look at your oil level as a precaution.
Paul

Yep, some fuel may have gone into the crankcase, and/or the muffler. If the latter it will be a blow torch should you get it started. Experience speaking. MikeV

The seat and needle came as a set. The bike ran on the front cylinder alone after removing a.gasket under the seat. The rear cylinder won,t fire with a full float bowl, new plugs and clean jets.