I have a 115 HP Mariner 2 stroke. I had the same symptoms a few years back. The choke wasn't engaging on start up. But once it did start it was fine, only on cold start did it give me problems. You can check a few dozen or more musts from spark to fuel and everything in between and not trouble shoot a problem, evaluation through elimination. Sometimes based on ones mechanical and electrical expertise it is, at times, prudent to take the boat into a certified Marine mechanic. Sometimes you have to "Call the guy." I thought I knew what I was doing until I took the Small Engine Repair course at a local Community College. Turned out I didn't know as much as I thought I did.
I know a guy that basically tore his engine apart to solve a rough start problem on his 1st cold run in spring a few years back. After monkeying around until the battery died he finally got the engine started with a booster pack but the 115 Mariner!!!!! would not get above 2500 RPM on the water. The new fuel line he installed had the arrow on the bulb in the wrong direction. Guess who?
You really wont know if a fuel filter is plugged until you change it and cut it open. They can be a pain to get at on some engines, I swear some design engineers are sadists. My Mariner is easy to get at, I change mine every year. I don't think it is 20 bucks. I have a list of items engine related I change annually and some more than once a year based on how many hours I run the boat. We don't have CAA or any towing service up here in Ontario where I am to come out and tow you in. You need to rely on other boaters if there are any, call a friend or the Coast Guard.
The anti syphon valve is a basic check valve at the tank that doesn't allow fuel to drain back into the fuel tank. You can search this site for more details on it.
A question, how much fuel did you have in the tank when you filled it? If it was near MT, yes you could have gotten some gum into the carbs from the bottom of the tank and I think that is your suspicion. It may still run rough even on a separate tank because your carb is now gummed up too. It isn't often that a engine runs great today and not tomorrow. Run a can of carb cleaner into the outboard through the temporary tank. It can't hurt. I would start there. If it runs better you will need to clean the carbs and change the fuel filter. Eliminate your first suspicion first. If not that make a comprehensive list to trouble shoot or as I suggested earlier perhaps "Call the guy."
? I am very handy and have done all kinds of repair. Can I repair this. where do I start? please help.I want to go out fishing again soon without spending thousands of dollars..