Why a rubber plug?

[RKM50]

Bike is a 1980 gs1100, mikuni carbs.
Why is there a rubber plug in the passage leading up to the pilot jet? Does the pilot get fuel from somewhere other than the bowl? I have a lot of experience with dirt bike carbs but have never seen this rubber plug before.
Thanks

 

[basketcase]

on these carbs if you look in the passage behind the rubber plug you will see a hole coming from where the main jet goes up. that is what feeds the pilot circuit and the plug is there to keep too much fuel from entering. without the plug it will run way too rich.

 

[RKM50]

Thanks, I did look but didn't notice a hole. I have to install some new main jets so I'll look again. The bike sat for six years so it would be good to check for any blockage there.

 

[Kaiser Sosei]

If the bike sat for six years do yourself a favor and while you have the carbs off the bike do:

A complete dissasembly of the carbs
Dip them overnight
make sure they are very clean and no clogged passages
get yourself new rubber plugs and maybe some float bowl gaskets, the plugs are dirt cheap
Go to http://www.cycleorings.com/#BS_Series_O-ring_Kit and order a new set of orings.
While you are waiting on parts adjust the valves
Make note of what jets you do actually have
synch the carbs,adjust the mixture on the carbs

If it still runs like crap, report back and let us know what mods are on the bike. If you have a stock airbox and exhaust you don't need larger jets. If you have pods, or 4 into 1 exhaust you may need larger jets, but you may already have them.

 

[RKM50]

A bit more history. The PO drag raced the bike, no street riding. It had an 4-1 open exhaust (no muffler) that has since been replaced with another 4-1 with a muffler. This caused the bike to run rich.
The engine was rebuilt before it was raced. It has Yoshimira (sp) cams and has been bored out. It currently has 152 main jets, don't recall off the top of my head what the pilot jets are. I have already been through the carbs once before the pipe swap and it ran really well. It has pod filters but I managed to find a stock air box that will go on soon. I received some 138 main jets and will try those as a start. It is a project and I have a lot of other things to do to it before I start riding it on a regular basis. There is a pic of it over in the projects/rebuilds section. http://www.thegsresources.com/_forum/showthread.php?t=194062
What do you "dip" the carbs in? Some kind of carb cleaner.

 

[Missile99]

Cool bike. The carb dip at AutoZone is Berryman's Chem-Dip. The big can for $28 even has a basket. Probably at most parts stores. They make the B-12 Chemtool.

Interesting carburetor design for sure. Without those rubber plugs the bike will bog and not make it past the mid rpm range. It would be a speed and acceleration governor all at once.