Where does the "mid jet" circuit go? (GSF carby)

[davej]

I have a 2006 gs5f.  3700 miles.  It had been sitting a couple of years so the carbs were gummed up.  I have had them off twice now and am still getting the lean surge/bog right at throttle tip in.  I can get rid of most of the surge by turning the choke lever just a bit.  The jetting is stock like the rest of the bike 130/60/17.5.   I have tried the fuel screws from 2 turns to 4 turns with no difference.

I can blow carb cleaner through the pilot jet circuit and it sprays out the two holes right under the throttle plate.  I took out the fuel screw and can blow retrograde out its hole and those two holes under the throttle plate. 

I am not sure I have the circuit that feeds the third hole under the throttle plate cleared out.  Is that where the mid jet feeds to?  (there are three orifices under the throttle plate; two right together and one a couple of mm toward the throttle slide)

Its hard to blow through the mid jet because there is a large vent hole at the top of the fuel bowl that the air rushes out of instead of going through the circuit.  The mid jet is clear but it looks like there is another orifice in the housing, deep to the actual jet.  does that part actually come out? (emulsion tube) 

I just want to be sure the carb is actually cleaned out before i change jets around too much.  But if I cant find any blocked circuits, I am not going to have any other options. 

Also, is there a thread explaining all the vacuum circuits on top?  The carb sticky hasn't addressed the F carbs yet.

[jmelchio]

I've wondered the same thing. I have the same bike and I looked in the Haynes manual but I don't see any references to the mid jet in either text or diagrams. They talk about the main jet and the pilot jet but not about the mid one. I thought that maybe the mid jet was the same as the needle jet but then I noticed that the needle jet is also present in the 2 circuit carbs so that would not make sense.
I ordered new jets to make my bike run a bit richer (20/60/135) but with that I don't have to change the mid jet so it's not a real problem at this point but I'd really like to find out anyway.

Can somebody tell us which part number on the image below is the mid jet?

[davej]

On this diagram its part 27, listed as a "starter jet"

http://www.cheapcycleparts.com/model_years/3902-suzuki-2006-gs500f/assemblies/124927

[jmelchio]

On this diagram its part 27, listed as a "starter jet"

http://www.cheapcycleparts.com/model_years/3902-suzuki-2006-gs500f/assemblies/124927

Great, thanks!

[davej]

Well I pulled the carbs again.....

I traced the circuit and indeed the "mid jet" is actually a start jet as the circuit goes up to the choke valve.  I guess it could come into play at other times depending on what all those vacuum hoses do at the top of the carb, or maybe it communicates with the main jet circuit somehow?

[rkjjeep]

Dave - explanation for the vacuum valves on top of carbs:

http://gstwins.com/gsboard/index.php?topic=57903.msg655868#msg655868

[davej]

hey thanks. 

quoting the wiki:

2001 - 2007 Carburetors

The advantage of these carbs are the inclusion of a Mid Main Jet that allows finer tuning of the fuel to air ratio of different throttle openings.

Where does this info come from, the service manual?  (I don't have one )