Re: 2008 Tohatsu 9.8 4 cycle - low load stalling
Glad you found the problem.
You are a victim of junk (or old) gas. We don't know for sure that your carb-crud can be traced back to it having been E-10. One thing that we do know at this point is that the fuel quality -- at some point -- was below par. The gumming may not have been caused by alcohol. If you did not drain the carb over the winter, the problem may have started in the off-season, and then shown itself this spring.
Although it came from a high volume station, there is a possibility that the fuel wasn't the best when you got it, especially if the station tank was filled (and churned up) just before you bought your load of fuel. It's plausible that the container you filled at the station may have had some crud or other contamination as well. In the future, verify that you don't gain any moisture aboard the boat. If you can keep the tank out of the sun (and you should), keep the vent closed when not running. A lot of small OB tanks sit for days/weeks/months before a full tank is run out, and moisture gain at the boat does happen sometimes.
Running a water-separating filter, such as your Racor is good. Be sure that you run a 10-micron element, which helps reduce any suspended water from making it to the carb. Again, we don't know for certain that water or alcohol was involved. We only know that you somehow got varnished jets in the carb.
These motors run fine on 87 octane; Premium doesn't seem to do anything better. Some premium blends may have additional detergents or similar additives, which probably doesn't hurt. We have been recommending K100-MG stabilizer for a couple of years now, and it helps a lot with E-10 phase separation, especially in bigger tanks, where the fuel sits longer. But... I have one fleet customer who repeatedly gets water contamination. Still not 100% sure of the source of his problem (could even be sabotage), but I have seen gel/goop/junk in the carbs of his motors multiple times.
I idle my 9.8 a fair amount, and have not seen any gumming issues as a result. These motors run on the cool side. Also, the carb runs a lot colder than any place else in the motor, because of the incoming cold air stream, and the fuel atomization in the venturi, and the trickle of incoming fuel from the needle valve. I doubt that idling promoted gumming in your carb -- just detected it.
Running the carb dry is good practice, especially if you expect to be away from the boat for a few days (or longer). The 9.8 sips fuel so slowly that you may find it takes quite a few minutes to run it down. Also keep in mind that this won't completely empty the carb bowl -- it will only get the fuel level down to the bottom of the carb body -- which will indeed eliminate varnishing in the emulsion tube and jets. Draining is better of course, but I haven't seen the need for that during the season.
See if you can find a gas dock that advertises "No Ethanol" on their pumps. We have two of these in Buffalo, and the folks who run that fuel have fewer problems than those who run auto station gas.
Hey pvanv, thanks for the thoughts.
I'm finally running again and maybe a bit wiser though far from satisfied with the situation.
- The Racor is new and clean, probably does nothing to help the situation.
- I've used only fresh/premium fuel from a high volume auto gas station.
- The two small jets were gummed so badly that overnight soaking still didn't clean them out.
Things I'm thinking of now to prevent the ethanol problem:
- Run it dry everytime I leave it
- Will look for the drain screw you mention on the bottom of the bowl
- Looking for the right additive to run, so far haven't found any conclusive suggestions
- Avoid idling. I idled for 15 minutes the day the gumming came to a head and I'm thinking that the engine/carb got hot with low cooling water flow and that evaporated the fuel but left the gum in the small jets.
- Do everything I can to prevent the EPA from approving or mandating E15 (E10 is the mandate today and a 50% increase in corn is going to be hellish for anyone with a small engine).
God I loved my old Yanmar 1GM10 - 6 years and it never failed, all I had to do was change the oil, filters, and put diesel in. Too bad it weighed 350# for 10hp vs. this 10hp Tohatsu that weighs 90#.
