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I have 2 Yamaha 9.9 on the same boat (cat)! Easy problem. The low speed circuit is clogged. Removing the carb and cleaning is not difficult (DIY).

a. Draining the carb every time is urban legend. That instruction is for long-term storage and is not relevant to this motor. In fact, the PO did that and had all manner of trouble with the carbs. Since running the engine dry merely ensures that the carb will dry (unless you open the drain it is not truly dry when it stops) and form varnish, better to leave it full for a few weeks.

b. Pull the carb again and make certain the low speed circuit is REALLY clean. Blast every crany and every passage. remove and reinstall the jets if possible. IF it is an older model where the idle mix is adjustable, remove the screw, clean the hole, and reinstall (count the turns on the way out).

c. Look for pitting in the carb bowl (stains and pits on the aluminum, in the bottom). With e-10 these are common. Stabil is not a highly rated corrosion inhibitor and will not help with this. In stead, try biobor EB or Merc Strore-n-start. Also Seafoam.

d. Clean the tank. Also check the filter and replace. Adding a secondary filter (raycor) is a good idea. And vent driers help. Anything to keep the fuel clean and dry.

I haven't had a carb problem in years. Had plenty before.

Sail Delmarva: Gasoline Additive Corrosion Testing

Sail Delmarva: Gasoline Filtration... and Vent Filtration Too?
 

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Agree, draining every time may be overkill. However, I forgot to drain for over the winter storage once & it got me, what a mess. So, how long between uses before draining? I really don't know. I drain if I am not going to run it again for about a week, and have not had any fuel related problems for many years, it just takes about a minute or so, & is easy.

Your mileage may vary. :D

Paul T
I make certain I sail every month :))). That seems to help everything.
 

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I have to confirm this point. On the advice of my mechanic not to run carb dry....
I use a Mercury 6hp four stroke. I use Valvtec ethanol fuel treatment. Have not run my engine dry all season and it always starts, 2nd or 3rd pull. I use premium grade gasoline. I think the key is a good cleaning at the start of the season, quality gasoline and use of gas treatment. I haven't had a problem starting my outboard in three years using this stuff. And sometimes my motor will sit for two weeks between uses. Ps...put my boat in mid May and still no problems.
Chris
Valvetec was another that got all excellent anti-corrosion ratings in the Practical Sailor testing.

With ethanol gasoline I many are under weighting the effect of corrosion on carbs. Aluminum builds this nasty gel very quickly, and cleaners can't dissolve it. Whereas varnish used to be the main worry, with modern fuel it is less problematical. The new problem is ethanol corrosion, and these additives can stop it dead in it's tracks.

Always check a problematic carb bowl for pitting in the bottom; if you see pits, you know at least part of the problem.

The other solution is controlling tank venting (reducing water absorption), but that is another topic. Even dissolved water has been shown to dramatically increase corrosion. The gas (or diesel) does NOT have to separate.
 
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