10 September 2012

Fixing my Tohatsu Outboard

My Tohatsu 9.8 outboard stopped starting last month.  This was very unusual because that is a great motor, and it has always started on the first or second pull since I bought it 3 years ago.  I decided to blog about the repair in the hope it helps someone with a similar problem.  The night I finally figure it out, there was this incredible rainbow that ended right on my dock.  Clearly, this was a sign.  (I just hope my dockmates are ok with me bringing animals 2 by 2 down to the slip...)

So I have been troubleshooting the problem.  The motor will turn over, but won't start.  First thing was to swap out the fuel tank and hose for a spare I had laying around.  The other hose was a little old and I wondered if it had some air leaks in it.  Or perhaps the gas in the tank was too old.  But switching to the other tank and hose did not solve the problem.

Next up was to test the outboard engine for fuel, compression, and spark.  

I pulled one of the spark plugs out, made sure it looked clean, and holding the insulated wire, I touched the end of the spark plug against a bolt on the engine.  I pressed the start button on the engine and could see the steady spark in the spark plug.  Not a spark problem.

Next I pulled the spark plug out and set it safely aside.  I stuck my thumb over the spark plug hole and turned the engine over again.  I could feel the sucking on my thumb, so it was not a compression problem.

Then I slipped the spark plug back in and turned the motor over a few times.  When I looked at the end of the plug, it was dry, which made me question whether it was getting fuel.  I also pulled the fuel supply hose off the carburetor, and pressed the bulb.  Fuel spurted out, so I knew the fuel was making it to the carburetor.

So fuel was getting to the carburetor, but not into the cylinder.  I pulled the carburetor off (it was very easy, just undo the fuel hose, the two linkage rods, and then remove two long bolts that connect the air intake to the carburetor to the engine block.)  One poster on the catalina 25 association forums mentioned that he was able to remove the carburetor with the boat in the water.  This is risky, but anything that gets dropped overboard become the unretrievable property of one Davy Jones.  But I decided to try it anyway.

I brought the carburetor home, picked up a can of carburetor parts cleaner, and went to work.  First I took pictures with my phone so I could see how everything went back together.  Then I removed the four screws on the bottom of the carburetor and removed the bowl.  Next I removed the two brass screws that hold the fuel jets.

Sure enough, the idle speed jet was covered with a thick varnish of residual fuel.  I cut some copper strands from various pieces of electrical wire and probed all the holes in the jets until they were clear.  Then I dropped the jets and screws in the carb cleaner for two hours, agitating the parts every half an hour.

Then I cleaned off the parts, put them back on the carburetor, and headed down to the marina.  Everything worked perfectly!

So how do you prevent this from happening?  I just need to remember to unplug the fuel line between the outboard and the gas tank each time I finish sailing.  Then let the outboard run for a minute until it burns all the excess fuel out of the carburetor bowl.  As long as the carburetor is empty, there is not fuel to evaporate and leave a varnish plugging the jets.