2020 3.5 HP merc only runs at half choke.

[Jhayes780]

Ok so I took it out yesterday, it’s a mercury 3.5 4 stroke. previously it was owned by someone that used it for 45 min then decided he didn’t need it and it sat for a year. I got it started and ran it in a trash can at NO CHOKE after warming up. I got on the water and it worked for a bit but then only operated what sounded like normal if I had the choke half on. As the day went on it got worse and now I’m trying to figure out the issue. I got home tan it in fresh water and added some sea foam to try and clean it out and now it runs at high rpm or not at all. Any help is much appreciated

 

[airshot]

Moisture in the fuel, mabey some crud...probably a gummed up carb from sitting. Previous owner did not run out or drain carb before storage. Clean tank and fuel system thoroughly, probably gummed up.

 

[QBhoy]

Hi. I had one of these. Terrible things for getting issues like that. Especially known to take oil into carb, from sitting in storage. Even sitting the correct side up…terrible for it. The solution is a proper carb clean. After a manual carb clean on the bench…it still didn’t run perfectly. I had to run it through a ultra sonic cleaner. Was all good after that…until the next time I sat it on its side !! Ended up selling it.

 

[Jhayes780]

Carb is clean, cleaned out gas tank, it idles well now without choke. However if I engage the throttle quickly it dies. If I slowly engage the throttle I can get to about 3/4 throttle but it will die at full throttle. Any idea?

 

[Lou C]

If I’d didn’t do this before but does it now, then either the idle or transition system in the carb is partly blocked. We had this with our Suzuki we bought from new. Dealer replaced carb same thing. Brought it back again service rep adjusted idle screw better but not perfect. After warrantee I dug out the epoxy they put over the screw to keep the customer from adjusting it and…adjusted so it ran RIGHT! Fine ever since.

 

[QBhoy]

Did you US clean it. Sometimes needs it. Or at least done again.
I’d also say that I had to mess with the settings a little too. You’ll maybe need to break into the anti tamper thing if it still has it covered.

 

[Fisherman6]

Carb is clean, cleaned out gas tank, it idles well now without choke. However if I engage the throttle quickly it dies. If I slowly engage the throttle I can get to about 3/4 throttle but it will die at full throttle. Any idea?

These engines are very fuel fussy. Once you get the carb cleaned, use only stabilized ethanol free premium fuel and never leave any fuel sitting in the system for any length of time. The manual lies!