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Old 22 July 2007, 12:17   #1
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Country: UK - England
Town: Bristol
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2-Stroke Idling Problem; which bit needs replacing.

Hi,
Just taken the RIB into Bristol docks to see if the running fault under load I have had is gone.

Well, it sort of has .

I have a problem now where the engine will run at idle, then get very lumpy, then stall.

With the cover and airbox cover off I can look into the three carbs.

It's a suzuki DT85 by the way

Looking into the carbs, past the choke flaps, there is a vertical brass round bar/tube. At the base of this bar is what looks like black plastic about 10mm tall and 6mm diameter.

Now, Carb two has fuel bubbling up out between the black tubing and the brass tubing which seems to be flooding the carb, creating a little puddle in the air intake, and I think causing my problem. No fuel is appearing from Carb 1 or 3 in the same way.

Anyone any idea what's going on from this marginal description?

Cheers,

Orve.
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Old 22 July 2007, 13:33   #2
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Country: UK - England
Boat name: Angel-B
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Engine: Suzuki 9.9HP
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My experience is almost entirely with motorcycle engines rather than outboard engines, but sounds to me like (in decreasing order of likelihood:

1. Float valve not seating correctly - dirt / contaminated
2. Float valve / seat worn
3. Float leaking

Drain the fuel out of the float bowl if poss, then remove the bowl. The float will be on a pivot, usually attached to the valve by a little bit of spring wire (delicate). Slide the pivot pin out carefully and remove the assembly, making sure not to drop any bits.

Check the conical tip of the valve and its seat to make sure they are clean (IME the valve seat should unscrew from the carb body) - if the engine has been standing for a while it may just be gummed up. Give the float a shake to make sure you can't hear fuel sloshing around in it. If you can, replace it.

HTH,

Chris
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Old 22 July 2007, 15:46   #3
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Hiya, I had a similar problem with my 135 Mariner that displayd the same symptoms. With the carb cover off, fuel was spitting out of the bottom carb at idle speeds, causing engine flooding in the bottom 2 cylinders at slow speeds. An adjustment of the float switch cured this.
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Old 22 July 2007, 15:52   #4
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Thanks Chris, I'll take a look.

BigNeil:
Quote:
An adjustment of the float switch cured this.
How is it adjusted?

Cheers,

Orve.
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Old 22 July 2007, 17:55   #5
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Quote:
Originally Posted by Orville View Post
Thanks Chris, I'll take a look.

BigNeil:


How is it adjusted?

Cheers,

Orve.
Again, going by motorcycle engines, you need to take the carbs off and invert them - normally, the fuel pushes them up - when you invert them, they drop down, closing off the float valve. The owners manual specifies the float height - usually measured from the float bowl mating face to the 'top' of the float (when inverted). Without a manual, all you can check that the float height is the same for all carbs - if on the problem carb the float height is less, there's your problem. Usually it is a case of carefully bending the little metal 'tang' that presses on the valve.

Cheers

Chris
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