Engine stalls when cover replaced on T9.9exrw 1998

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Magic Time
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Posts: 36
Joined: Tue Oct 17, 2006 12:43 pm
Location: Toronto

Engine stalls when cover replaced on T9.9exrw 1998

Post by Magic Time » Thu Sep 05, 2013 4:05 pm

Engine rpm reduces slowly to a stall when the engine cover is installed.
When I put the engine cover back on and seal it locked the engine rpm reduces from a 1000 rpm idle to about 400 rpm, sometimes staling. This is an immediate reaction of less than 30 seconds.

What I have tried so far.
The Carburetor has been totally disassembled, all parts ultrasonically cleaned and a Yamaha rebuild kit installed. The electrothermal choke has been tested and found functioning normally.

One outboard mechanic’s first comment was that I have a hole in the gasket that is in between the power head and the exhaust and that the carbon monoxide is starving the motor.
I have Referenced 3 shop manuals to find out more about the exhaust system and how it works. The only reference that I can find is referring to
the “Exhaust / Water Jacket Cover” that is on the port side of the power head. According to the manuals there is water cooling this cove. I have not seen any sign of water leakage during running.

Can any one tell me exactly from where carbon monoxide could enter the engine cavity that is enclosed by the engine cover.
Has anyone experienced this problem or would anyone be able to direct me to illustrated diagrams of the parts that make up the over all exhaust system.
If there are already posts on this subject please list the names so I can refer to them.

Thanks so much
Magic Time

Magic Time
1st mate
1st mate
Posts: 36
Joined: Tue Oct 17, 2006 12:43 pm
Location: Toronto

Re: Engine stalls when cover replaced on T9.9exrw 1998

Post by Magic Time » Thu Sep 19, 2013 10:44 pm

For the mechanical owners out there.
I went ahead and pulled the power head off my T9.9 to see if I could find the
source of my troubles as described above.
The following are a series of photos.

Photo 1 is of what Yamaha calls the Guide Exhaust Plate.
This is what you see if you remove the Power head.
Unfortunately I had no idea that it was such a trap for dirt, salt. Even though I used
A 1/8 inch copper tube on the end of my wash hose to try and spray
under and around the power head there was a significant build up of muck.
Guide, Exaust Plate.jpg
Guide, Exaust Plate.jpg (70.25 KiB) Viewed 2812 times
Photo 2 Is to show the hole in a indented part of that plate.
I was un aware that this indent is there.
When I first looked I could barley see the hole. It looked tiny until I removed
the 1/8” of muck. This is where carbon monoxide
has been entering the cover area and starving the motor.
hole in Plate.jpg
hole in Plate.jpg (75.38 KiB) Viewed 2812 times
Photo 3 Note the right end of photo were the muck Is cleared away.
There is a hole about 1/8”dia.
This hole is a drain that is suppose to drain the
Indented portion of the plate. It is very easily plugged.
drain hole in indentation.jpg
drain hole in indentation.jpg (46.58 KiB) Viewed 2812 times
Photo 4 The top hole, just below the cover lock is the exit for the above mentioned drain hole.
You can try and push a pipe cleaner threw the hole but there is a right angle bend upward to
access the Indented area. If you make a bend near the end of the Pipe cleaner you should be
able to wiggle it up the hole to attempt to keep the drain clear.
Exit drain hole.jpg
Exit drain hole.jpg (43.53 KiB) Viewed 2812 times
Unfortunately It has become obvious to me that a spray tube that will reach
into this depression is necessary to keep the indentation clean of muck.
The first spray tube that I use was not long enough.
I will make a new 1/8” tube from flexible copper and shape it so the end can reach this indentation.
Also the drains around the perimeter of the center casting need to be kept clear.

If you are not thoroughly spraying this area under
And around the power head you will be risking a
Hole developing from corrosion.

Hope this will be helpful for all.
It was an expensive lesson to me.

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