I have been having a series of problems with my 2002 Yamaha 9.9 4-stroke
outboard, mainly with blocked up carburetor jets. This season, I have had to strip
them down three times to clean the jets. I have been putting Stabil and Mercury
Quick Silver Cleaner in the gas tank, and that seemed to help for a month, until
today, while out on Lake Michigan the engine stopped running again. I don't know if
all 4-stroke engines behave like this, all Yamahas, or just my particular engine. I
expect better performance from an engine costing over two thousand dollars.

Sorry for the repeated posting, but the stupid forum
software kept coming back telling me I had an error
in posting.

i assume that you are using a water seperator/filter inline with your motor? also then you should upgrade if possible to the 10 micron filter offered by yamaha. it is obvious your motor is getting junk from your tank, you should try to clean it.

What do you recommend to flush the gas tank. Will
some fresh gas do the job? Any opinions on additives to help preserve the gas and keep the jets
clean? I have used Stabil and Sea Foam to keep the
gas fresh. My outboard mechanic recommended a product from Mercury called Quick Clean to keep the
jets open.

Sherwin,
If you are burning an ethanol blended fuel, that could be the source of your problem with the carbs clogging up.
Take a look at this article:

http://www.boatus.com/news/e10_0706.htm

If you are having to use ethanol blended fuel, you need to install a 10 micron water separating fuel filter in the fuel line. Racor and Yamaha makes one for small outboards.
Also, don't mix ethanol blended fuel with regular fuel that has MTBE. Once you switch to ethanol, avoid going back to MTBE fuel.
SeaFoam is fine for use as a cleaning agent and de-carbonizer and fuel stabilizer.
To clean out the old tank, just add a little fresh fuel and discard.
Good luck [img]smile.gif[/img] ,
Ken K

Here is the latest update on my problem. I cleaned out my tank and replaced it with
fresh gas. I also purged the fuel delivery lines and the carburetor of old gas. That
did not do the trick to start the engine. There were some orangish deposits on the
base of the carb after I opened it up. Also, some dark droplets were mixed in with
the old gas taken out of the carb. What finally did the job was running fine wires
through the low and high speed jets. It is working fine now, but for how long? I
think I might replace the fuel line for next year.
Ken says that I should be using
at least a 10 micron filter. My external Tempo filter is only 40 microns. I have no
idea what the filter inside the engine is rated for. The basic problem are these very
fine jets on the smaller horsepower ( 9.9) four stroke engines. Yamaha has been
making them for some time, but seem to be burying this problem. My fuel line is almost 10 years old, and although it is still flexible, maybe I should replace it. Could be that all these additives I put in the gas are breaking off some
crud sticking to the fuel line. I have made a practice of draining this fuel line every year I put the engine away for the season.