Just dealt with this same issue on a 2-stroke 15hp Nissan
(same as a tohatsu)
The choke issue tells you it is fuel related.
Choke pulled out = less air more Fuel= richer fuel mixture
Choke pushed in = more air less fuel = leaner fuel mixture.
If you pull your spark plugs and look at their wear/color youíll also get an idea of whether your running too rich or too lean.
Are you running the correct fuel/oil ratio? Youíll notice I burnt oil/fuel on spark plugs if thereís an imbalance.
Steps to resolve:
-check spark plugs for fouling (not likely the case here but itís by far the easiest troubleshooting step and will tell you a lot of info)
-Clean the carb with carb cleaner.
- then clean it again.
-Clean the in-line fuel filter (water likes to collect in there).
-Check your not pulling crud from the bottom of tank (if itís external).
-Check you have enough flow from
External tank if you have one. Those back flow preventer valves are t necessary and fail frequently.
- Check fuel hose especially if it is gray. Those gray hoses have a liner that is supposed to be ďimpermeableĒ to Ethanol fuels but they clearly are not and frequently get degraded and clog the line. I replaced with a standard black rubber fuel Hose (they work
on cars just fine and are much cheaper) Actually I did this twice as the first one I ordered had a defective primer bulb. This was what was ultimately clogging my fuel system and with a new hose the motor immediately started up.
I also adjusted fuel mixture screws (over time they can back out due to vibration) to get a better run. No harm in playing with these as you will be able to hear where the engine is happiest. Turn (while counting number or turns) until you begin to sputter then go back to where it sounds happiest. Note than at idle might not necessarily be where itís happiest while under throttle. It is better to run too rich than too lean.
Another issue with 2 strokes is that they like to be run a FOT and that is how the fuel/oil ratio is designed. With extended periods of idling you can frequently get issues with unburnt oil
in combustion chamber and that will slowly clog spark plugs. Where I am anchored a couple months of the year is a idle speed manatee zone and I have begun running motor at a 75:1 instead of 50:1 during those months and she seems happier. (This was advice
from dirt bike users)
Best source of info for 2 stroke
engines Iíve found is on dirt bike forums
. They are all two stroke motors that typically get run very very hard.