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Old 06 April 2016, 11:36   #1
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Yamaha 9.9D (now 15) stalls after decelerating

I have a 1983 Yamaha 9.9D (uprated to 15hp by the previous owner). It always starts first time - even after no use for a few months. It idles fine with no problems and accelerates and reduces throttle (up to about 3/4 throttle) with no problems whatsoever.

If I've been sat doing a high speed run for a little while and then decelerate quickly from full (or nearly full) throttle the engine often stalls and then is a complete pig to get started again.

I imagine that with the rapid deceleration I'm flooding the engine - causing it to stall and then be a pig to start again. I'm just wondering why this is happening and whether there is anything I can do to stop this.

Obviously, altering my driving habits - and not decelerating suddenly from full throttle is the easiest solution!
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Old 06 April 2016, 12:03   #2
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Is your bulb still hard and are your plugs wet when it happens
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Old 06 April 2016, 13:17   #3
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The bulb is still hard - haven't actually pulled the plugs after this has happened - as I tend to be in the middle of the lake - but will certainly have a look next time.
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Old 06 April 2016, 18:41   #4
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This is often caused by a slightly week idle mixture. Get the engine warmed up, give the boat a run and slow to a stop. Adjust the idle mixture screw - you'll find a week point (Screwed inwards) where there is a change of engine note and then (screwing it out) it will become good then a change of engine note as it becomes too rich. Find the center point of adjustment but then err on the slightly rich side and deffo not on the week side. It's in order to have a slightly rich idle mixture but if it gasses up and stalls frequently, you're probably too rich. Having said that, old school 2 strokes frequently don't idle continuously and require the throttle to be blipped to clear them.
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Old 08 April 2016, 17:43   #5
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Will give this a go - thought I was maybe running too rich already - as its a pig to restart once it stalls, but will err on the side of richness and see what happens
Many Thanks
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Old 09 April 2016, 07:40   #6
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Quote:
Originally Posted by jonathandorey View Post
Will give this a go - thought I was maybe running too rich already - as its a pig to restart once it stalls, but will err on the side of richness and see what happens
Many Thanks
Well, perhaps it is a rich stall but setting it up as above will ensure you've got it pretty much correct. But be realistic in that you're using 30 year old technology and 2 strokes of that era were not always as sweet as they might be.

The difficult hot starting may be a different issue - first stop for that is a hot cylinder compression check.
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Old 26 April 2016, 23:06   #7
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I would rebuild your carb.
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