1980-83 GS850 Carburetor Specs and Float Height Illustrations
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On this page:
Suzuki GS Series Carb Specs
Float Height Illustrations
CV Carb Jetting and Cleaning
VM Carb Tuning Guide
Fine Points Of CV Carb Internals
Shimming The Needle
Mikuni/Dynojet Conversion Spreadsheet
Vance & Hines Jetting Recommendations (PDF-600k)

GS850 Carb Specs: 
Measurements = mm (in.)
Carburetor type = Mikuni BS32SS
Bore Size = 32 (1.26)
I.D. No. = 45110
Idle rpm = 1050 +/- 100rpm
Fuel Level = 5.0 +/- 0.5 (0.20 +/- 0.02)
Float Height = 22.4 +/- 1.0 (0.88 +/- 0.04)
Main Jet = #115
Main Air Jet = 1.7
Jet Needle = 5D50
Needle Jet = X-5
Pilot Jet = #40
Bypass = 1.0, 0.8, 0.8
Pilot Outlet = 0.7
Valve Seat = 2.0
Starter Jet = #32.5
Pilot Screw = Preset (actually, these can be adjusted - start with about 2 turns out from lightly seated)
Throttle cable play = 0.5-1.0 (0.02-0.04)

Suzuki GS Series Carburetor Specifications:
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GS Carb Specs

On the GS Resources Forum there is a thread containing a collection of carb specs.  That thread is located here:

Mr. Tom R has collected this information in a handy Excel spreadsheet.  Download that spreadsheet here:  CLICK HERE.

(Note: If you do not own Microsoft Office, I recommend downloading the free Office-compatible suite from OpenOffice. CLICK HERE.)

Measuring Float Height:
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Here are a few helpful pictures, courtesy of Mr. Steve and Mr. bwringer, showing us how to measure float height.   

Measure and bend

A more accurate way of measuring fuel levels is to check the actual fuel height in the bowls.

Fuel Level Hose

The above is available from Z1 Enterprises or you can make them yourself.

Checking fuel level Checking all four fuel levels

Check your manual for actual fuel heights.

For CV Carb jetting, see the very informative article at Factory Pro.  Also see the carb jetting tips at Motorcyclecarbs.com, Inc.

Mikuni Motorcycle Carburetor Theory 101 - from Ian Williams Tuning

Here is a Mikuni tuning guide for the VM Series: http://www.mikuni.com/pdf/vmmanual.pdf

A general carb tuning guide from Delloroto Motorcycle Carburretor Tuning:

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Mr. shirazdrum (Chris) put together an HD Video Tutorial on Cleaning Mikuni CV Carburetors:

Here is a write-up on the ST (Slingshot) series of Mikuni carbs. It's a Gixxer.com forum thread with lots of pictures: http://www.gixxer.com/forums/showthread.php?t=159718

Or you can download a PDF version of all the pertinent information by clicking here.

Fine points of CV carb internals -
Needle jet vs. Jet needle
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(by Mr. Steve)

The needle that is held in place with a circlip and has the two spacers, is the "jet needle". It is located in the slide that is part of the diaphragm assembly. As the slide moves, the jet needle goes up and down in the "needle jet", sometimes called an "emulsion tube".

The "float needle" is, remarkably enough, somewhat connected to the "floats", those big things that regulate how much fuel is allowed to sit in the "float bowls". Once you have removed the floats, you can remove the float needle and inspect it. What you don't want to see is a groove around the tip. If the tapered area is all smooth, the needle is good. Now remove the housing the needle was sitting in by removing the Philips-head screw and pulling it out. THAT is where you will find (an) o-ring that comes in the (cycleorings.com) kit. While you have that assembly out, inspect the filter screen that should be attached. Clean it carefully and re-install it after you have dipped the rest of the carb parts. Put a drop of oil on the o-ring before inserting it into its bore to help prevent tearing it up.

Think you might have worn jets and/or needles? Click below for pictures and information.



Worn needle

Shimming The Needle
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(as explained by Mr. jimfj)

The shimming is acomplished by completely removing the slides from the carb bodies

Inside the top of the slide is a snap ring. Remove the snap ring and the needle will come out. On top of the needle is a nylon washer about 3-4mm thick.

Replace the nylon washer with smaller thickness washers of your choice. This creates a richer mixture or allows more fuel to flow.

Reassemble the slides and install them back into the carb bodies, making sure to align the tab of the rubber diaphram on the top of the carb body.

Put the caps back on the carbs and start her up.

Note: This isn't a substitute for jetting.  This is just a way to make the bike run a little richer and take advantage of the full power band. This procedure can be acomplished with the carbs on the bike, no need to remove them.

(as explained by Mr. Steve)

Remove the tops of the carbs. You might be able to just remove the four screws that hold the 'dome' on the top of the carb and lift it off. There is a soft rubber diaphragm right under it with a light-weight spring between it and the cap. Gently remove the diapragm, lift it out of the carb. Look down the center slide, you will see a circlip at the bottom. It takes a very long pair of needle-nose pliers (Sears, $10) or a good set of circlip pliers to remove it. Pull the nylon stem out of the slide, noting its orientation. When the stem is out, you will be able to remove the jet needle. There should be a thick nylon spacer at the top of the needle, then a circlip, then a metal washer, then a spring. The needle position is determined by the thickness of the spacer above it, so go to Radio Shack and get their bag of assorted washers (about $2). The smallest ones work perfectly. Stack up the washers to see how many it takes to equal the thickness of the nylon spacer (usually about 4). Cut that in half, put them on in place of the nylon spacer, put everything back together. When you put the diaphragms back in place, note that there is a tab on one side of the edge, it fits into a shaped area on top of the carb. Snug everything back into place, it should be good to go.

Mikuni Jet/DynoJet conversion spreadsheet:
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(Thanks to Mr. salty_monk)

Download a spreadsheet which will do the conversions between stock Mikuni jets and DynoJet parts (conversion factor: 0.9375).  CLICK HERE to download.

Thank you for your indulgence,


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