What does this Rubber Cap do...

[hydrasportsam]

I have a 2002 Yamaha 4-stroke (F40TLRA).
Go to any parts catalog for this motor - The Carburetor.
Item #8 is a Rubber Cap.

WHAT FUNCTION DOES THIS RUBBER CAP HAVE? They keep coming out of the hole they plug into (1 per carb). I've ordered & installed new ones. Correct part # for sure. Keep coming out.

The bottom of the carburetor bowl should almost touch the bottom of the rubber cap when the bowl is attached to the body whick keeps the plug from falling out. I measured everything an there's about 1/32" difference. All 3 of my carburetors have some how pushed these plugs out and it the bobbles around the bowl and hangs up in the float, runs rough.

 

[99yam40]

Re: What does this Rubber Cap do...

I would think that the plug forces the idle jet to get its fuel through the main jet, so that at upper RPM the motor would not be pulling gas through both jets out of the bowl causing a too rich situation. but this is only my opinion.