Carburettor mystery - identify this.

AndrewB

AndrewB

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My 15 month old Mercury 3.5hp 4-stroke outboard has been proving slow to pick up when the throttle is opened. Suspecting it might be a blocked jet, I decided to check the Keihin carburettor. The jets seemed fine, but lying loose in the bottom was the piece of black plastic shown in the photo below (alongside a 1 Euro coin). Can anyone identify it, please? Should it be in the carburettor at all and if so where does it belong?

Thing.jpg
 
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Yes it probably fits over one of the jet holes between the body and bowl. Have something similar in rubber that fits over the bottom of the intermediate jets on the carb in our 8 hp yamaha.
 
AndrewB said:
My 15 month old Mercury 3.5hp 4-stroke outboard has been proving slow to pick up when the throttle is opened. Suspecting it might be a blocked jet, I decided to check the Keihin carburettor. The jets seemed fine, but lying loose in the bottom was the piece of black plastic shown in the photo below (alongside a 1 Euro coin). Can anyone identify it, please? Should it be in the carburettor at all and if so where does it belong?

Thing.jpg
Click to expand...

Hi Its a common problem. There are two jets going into the main bowl. One larger than the other. This rubber bung goes in the smaller one. Glue it in place.
 
Dot's interesting.. Mate was having trouble with his new Mercury 3.5 and when we stripped the carb.....Guess what? That plug was loose in the bowl. Seems their quality control is not best. There is a hole next to the main jet it goes into and a recess in the bowl that holds it in. No way i would pop out by mistake, so factory screw up.
Just to add, after several problems with overfueling, found out that the filter in the tube from the tank was not located properly and there was fibrous junk that occasionally stopped the float valve from sealing. If you have one of these, go right through the fuel system. The factory clearly didn't bother.
 
its a common problem with not only this model of carbs but others with a rubber plug. The fuel shrinks the rubber and it drops out.
DownWest said:
Dot's interesting.. Mate was having trouble with his new Mercury 3.5 and when we stripped the carb.....Guess what? That plug was loose in the bowl. Seems their quality control is not best. There is a hole next to the main jet it goes into and a recess in the bowl that holds it in. No way i would pop out by mistake, so factory screw up.
Just to add, after several problems with overfueling, found out that the filter in the tube from the tank was not located properly and there was fibrous junk that occasionally stopped the float valve from sealing. If you have one of these, go right through the fuel system. The factory clearly didn't bother.
Click to expand...
 
steve66 said:
its a common problem with not only this model of carbs but others with a rubber plug. The fuel shrinks the rubber and it drops out.
Click to expand...
Hi Steve, the design of the bowl keeps it in place, I can't see how it could fall out unless the bowl was lowered, or, it was not put in originally. Since that strip down it has stayed in for a couple of years. It has not shrunk and is a twist & push fit into the hole.
And, the fibrous material was also in there from the factory.
 
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