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1997 Yamaha 9.9 four stroke issue


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 I have a new to me boat that came with a 1997 9.9 Yamaha kicker. The motor seems to run fine for a while then will chug for a little then stall. I can start it up again and run fine for a bit then the same thing will happen. I thought it might not be getting fuel so I tried priming the bulb when it would start sputtering but it stalled anyway. the gas line is connected to my main fuel tank with a tee fitting from the main line. Not sure if it has a low oil or overheating sensor.  Oil levels are fine and I changed the impeller a couple of weeks ago. I'm not familiar with 4 stroke outboards so any help is appreciated.

 Thanks, Rick

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was the priming bulb firm when you pumped it up?   how long do you have to wait to restart and how long till the second stall,    how old are the spark plugs

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The bulb is firm when I pump it. The motor will start right back up. Not really sure how long until it stalls again but its several minutes. I don't know how old the plugs are. could this be the problem even though the motor seems to run fine for a while? 

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Posted (edited)

plugs are easy to swap out,   it's worth a try,   the other thing you can do,  when is about to stall,  spray some silicone or starting fluid in the carb,   just an easy step to further diag the fuel system,   [fuel pump, or carb float]

Edited by tech2526
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6 hours ago, Shakemsam said:

Try it on a different fuel supply before you do anything else. If nothing changes, clean the carb.

have you checked the bulb on the gas line when the Motor dies to see if the bulb is still firm?

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Ran it again today. Turned off the gas to the main engine and it ran fine for an hour then sputtered and quit. Started right back up but quit again pretty quickly. I don’t know if it has an anti siphon valve.

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 Would a check valve work on the main gas line? I thought it might be easier than having to go into the bilge to turn off the fuel every time. I would keep the shut off valve but have the check valve closer to the t fitting.

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Posted (edited)
25 minutes ago, Bad Habit said:

 Would a check valve work on the main gas line? I thought it might be easier than having to go into the bilge to turn off the fuel every time. I would keep the shut off valve but have the check valve closer to the t fitting.

yes.use a 3 way valve be sure to doub!e clamp  and if its under the floor be sure to use uscg approved inboard fuel line

Edited by Tradman
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if you're using a regular fuel line with a bulb and if it's very old, they have an inner layer that tends to separate and after the motor runs for a little bit the inner lining will collapse shutting off fuel flow. once the motor dies the inner lining opens back up. my first repair would be to replace the fuel line and bulb with a new one unless it's been replaced recently.

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