Recently purchased a boat and the motor runs fine when I can get it going...it just doesn't want to idle and has difficulty starting. Had it out last week and ran it for about a hour up to about 40mph. Stopped to refuel, and couldn't get it started back. Took it home and I could get it to stay running on the hose if I kept the RPMs above 2000. The compression is good 100 +/- 5 on all four cylinders. Spark good on all cylinders. I noticed there was some gas dripping down from the air silencer. So I just finished rebuilding the carbs....thinking they may have been gummed up or a float was stuck. Now I can't even get the motor going even by keeping the RPMs up, and there is still gas dripping from somewhere, kind of looks like the carbs are getting flooded?
If your cold-start fuel primer is not working, it will make your engine a bear to start when cold. This system is activated when you push in on the key when cold starting. Check the primer hoses to make sure they are pumping fuel when the key is pushed in. Once the engine is warmed up, you should not need to choke it. When idling, the carb butterflys are closed. This means the fuel must pass through special small idle passages internal to the carbs. If they get clogged with dried fuel gelatin, the engine won't idle properly. You can't visually check these passages when rebuilding. Once you move the throttle even slightly, the mid and high speed jets activate and the engine will seem to run fine. You may need to pull the carbs apart again and make sure the idle passages are clear-an aerosol Gumout type fuel cleaner works well. Gas dripping from the carbs may mean the needle and seats are bad. These normally get replaced when you overhaul the carb and put in the new carb kit parts.
I think the primer is working, I can hear the solenoid clicking on when I push in on the key. I cleaned the carbs really good, soaked in carb cleaner, ran some small wire through all the openings, and then blew out the opening with compressed air. It doesn't look like gas is leaking from the carbs exactly... more like unused gas is being spit out of the lower carb through a drain hole in the air silencer after it tries to crank.
Your airbox drain is connected to the bottom cylinder of the powerhead by a small drain hose. Make sure it's there and properly connected. It's purpose is to scavenge any excess oil/fuel the comes out of the carbs and insure that it gets combusted (recirculated) in that lower cyl. On the early 70's crossflows, it wasn't unusual for aome fuel/oil to leak, drip out of these early carbs. Your engine has newer type carbs that don't tend to leak fuel as badly as the early ones. If yours is leaking enough to see, it bears further attention. If you see fuel spitting out of one carb, visually check the reeds for that cylinder to make sure the petals are all still intact and functioning. When rebuilding carbs, I prefer to remove all the jets and visually inspect them, blow out the passages-then reinstall. When I know a carb is acting up, spray one passage on one carb with an aerosol cleaner, then the same passage on the other. Watch for is the spray patterns exiting out the other end of the hole. The spray patterns should be identical. Then go on to the next passage, etc. A clogged hole will have a reduced spray pattern you can see.