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Just thought to update on latest progress regarding my fuel/carb/idle issues...

Pulled the carb's of Saturday and began the re-build. My suspicions with the bottom carb were realized immediately upon removing bowl cover.

Float area was glazed with a lite green film along with the primary jets. The float needle had become stuck within it's seat. I removed the top cover and discovered in a small partioned cavity (I think it's an air metering port) of the actual carb body what I would refer to as a type of calcification or rust on the interior walls of this cavity. Moisture from ambient air must work it's way somehow into this area, the other 2 remaining carbs presented the same condition.

After carefully removing the pilot and main jets along with the pilot tub I observed that they were heavily coated and their orifice's beginning to clog with contaminents. I found traces of the small dark particles in the jets and especially on the float needle and seat (these were the same dark particles first observed/found in my filters).

The remaining 2 carbs were found to be in much better shape as far as the contamination but, the film was present and the jets would benefit from a proper cleaning.

Rebuild is complete, new seals/gaskets, float needle assembly and float heights were checked to be within Yamaha spec's @ .556" - .562" (+/- .020).

I will be replacing engine mounted fuel pump to complete repairs and re-assembling this week.

The carb rebuild is quite simple as many posted on the numerous forums I viewed. A 1/4 drive 10MM socket's front outer diameter will need to be slightly modified/reduced for access and removal of the float needle seat. The more tedious task is gaining access to the carbs if your Yamaha 90 has the oil injection reservoir mounted by and onto the carbs as is with my outboard.

The experience is great and it will familiarize one with the outboard.

I will post on engine performance.

Angel M.

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Black particles in your carb sound like they are parts of fuel lines that are deteriorating due to ethanol.

I just rebuilt a set of carbs over the weekend that were full if those same particles.

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I have had the same experience with my engine and fuel lines. Even with a new fuel line, the inner core deterioted in 2 years. I think the new fuel I used 2 years ago was not correct for my application, I bought some off the shelf stuff from West Marine (it was silver/grey colored on the outside).
I just ordered up some A1 rated fuel line based on reccomendations here and on other sites.

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Fortunately it wasn't my fuel lines, I replaced them about 3 or so years ago (and fuel tank) with ethanol resistant brand. The fuel line I used is Sierra Silverado SS 2000 (3/8" I.D.) SAE J1527 Alcohol Resistant, fuel tank is a Moeller Marine 18 Gal. above deck model.

I'm convinced it was the primer bulb that had degraded. I have replaced it with an E10/E85 resistant model made by Marpac marine. I cut the suspect primer bulb open to investigate and it was discolored and flaking. When I installed it about 3 years ago with the fuel lines and tank I thought it was rated for ethanol.

Oh well, live and learn...

Angel M.

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Dauntless - take a look at my personal page - just added a picture to show what happened to my 2 year old fuel line. The inner core deteriorated and blocked fuel flow. First symptom was a collapsed fuel bulb. I cleared the block and ran the boat successfully, I will replace the fuel line this winter. Not sure if this is the same fuel line you have installed.

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Hello Sebastian, no that's not the same fuel line I used but same make Sierra.

The fuel line I used is labeled:
Sierra Silverado "SS 2000" SAE J 1527 Alcohol Resistant Fuel Hose 3/8" USCG Type B2

Its a fairly thick walled hose and a darker gray than the one you pictured. There is a good view (and info detail) of my fuel line in my "Fuel Tank" project album, take a look.

Thanks for the info...

Angel M.