BLUF:  I need to be more observant and pay closer attention to the small details.

I enjoy working on carburetors.  They are engineering and manufacturing works of art.  No other engine part has more effect on how well an engine runs than the carb.  It is amazing to me that they work at all.  They have to deliver a precise mixture of fuel and air over the entire engine RPM range.  The tiniest little thing can cause one to operate improperly and it requires a keen eye to find it.  My friend Larry has an eye for such a thing.  It is amazing to me to watch him disassemble a part and point out the slightest flaw that indicates the cause of the malfunction.  It might be a tiny crack in an o-ring or a faint discoloration on a bushing.

Recently a friend of mine had just complete rebuilding the carburetor on his 25 Hp outboard motor.  He installed the newly rebuilt carb only to find that it leaked gasoline profusely and he asked me to help him find the source.  It turned out to be coming from the carbs fuel bowl vent and upon further inspection fuel could be seen streaming up and out of the main jet port within the venturi.

Main Jet Passage

So I am thinking to myself that the cause had to be a malfunctioning fuel bowl float valve.  What else would cause fuel to be pumped up and out of the fuel bowl vent?  So I removed the carburetor, drained the fuel from the bowl, and turned it upside down so that gravity would close the float valve. I then tested the valve by blowing into the fuel inlet.  Boating Lessons Learned – I really should have taken the time to find a clean length of fuel line to blow through because gasoline does not taste very good :-).

But huff and puff as I might the valve proved to be sealed tightly. Oh well.  I was sure the valve was the problem.  But with no other leads to go on I removed the fuel bowl and inspected the float valve assembly.

Float with Needle Valve Exposed

I noticed that the pin that the float pivots on was slightly out of place and I presumed that possibly it’s travel was being impeded.   I put it back in its groove, reassembled the carb, and tried it again.

Darn, it still leaked.  After trying a couple of other things only to achieve the same results I was stymied.  I sat there for a while scratching my head and for the life of me I could think of no part other than the float valve that would create these symptoms.  So with no other options I asked my friend to go get the old needle so we could look to see if possibly the kit came with the wrong one.

While he was gone I piddled around taking the pictures that you see here and got some unsolicited feedback from Molly.

Where did she learn so much about carburetors?

Retaining Screw Missing

How could I have missed that? That little detail had been staring me in the face the whole time. While I was happy that I had discovered the root cause as to why the valve was not functioning I was disappointed with myself that I was so unobservant.

Of course it would have helped if we had a manual on the carb that laid out the rebuild steps in detail with accompanying photographs.  The devil is in the details on such an intricate mechanism. HP Books publishes manuals for the more common carbs.  I recently broke down and decided that I needed to learn more about the Rochester after spending $600 farming out 3 of them for rebuild.  The price of the book plus a rebuild kit is about half what I had to pay for someone to rebuild just one of these carbs.

My friend was able to locate the missing screw and in no time we had it back on the engine and running fine.  But I am still kicking myself.  I bet Larry would have noticed the missing screw right away.

Boating Lessons Learned:  Troubleshooting Requires Attention to Detail.

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