Every spring I have a problem keeping the Lark running without continually pumping the pressure tank primer button. After running it a while that way the 1st day, it will usually be OK for the rest of the year. I've switched tanks with known good ones, changed o-rings, and checked for pressure leaks everywhere w/ soapy water......No leaks. It doesn't seem to build as much pressure as my other motors, and it won't hold pressure when I shut it off. I've also had the motor apart to check the pressure check valves and they look fine to me. Any thoughts?
If as you say it's only runs that way the first day it sounds like you have a gasket or seal that is drying out over the off season. Have you checked the gasket on the fuel tank, the one where the black pump, gauge, and fill cap are located. There are only a few areas that could dry out. Those "0" rings in the fuel connector to the motor are a special size and I haven't found anything at local stores to replace them so you must get them from and OMC dealer. Put a little dab of grease on the fuel connector plug openings to lube and soften them. I've circled some possible leaky areas that might dry out. If it's just on the fuel tank itself you can take the things apart and apply some permeatex non hardening gasket stuff from a tube. Check for a cracked or brittle area in the air line on the motor around the connections. Maybe a warm motor softens up the hose and re-seals it enough for the season.
Don't forget that you have to have the gas tank cap tightened down good to keep the pressure in the tank while running. When you shut the motor down you should be able to loosen that gas cap and you will hear the pressure releave.
Yes, the fuel tanks have been checked. They also work with other motors. I've changed the o-rings (w/ OE OMC parts) and checked everything with soapy water. I really think it's in the motor somewhere. I've checked that out also. I just had a thought that I should eliminate the anti run away switch and see if that helps a little as it could be leaking. Thanks for the input. I will definitely be using grease to install the fitting from now on.