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Upgrades: Rejetting

Intro

This page contains sections on "how", "why", and also "to what settings". You should probably read ALL of the sections before even picking up a tool.

How

This is a good pictorial how to: Poor Man's Rejetting Pictorial

There is also, of course, the canonical site: http://www.gstwin.com/rejet.htm

VERY detailed video of the process is at http://www.youtube.com/watch?v=AJh1hxNf7BA It is for "jet cleaning", not replacement, but it's basically identical, right down to removal of the jets. Just skip the cleaning part!

While taking the carbs apart in all this, if you have the original soft, brass, JIS type screws, you may want to replace them with easier ones, as mentioned at Maintenance.FreeSeizedCarbScrews

A good place to order jets online seems to be http://www.sudco.com/mikunijets.html. For Pre-2001 models your mains will be N100.604 and your pilots will be N151.067. For 2001+ models, your mains will be N102.221 and your pilots will be N224.103 or VM28/486. Although they have a website you must still call them to order. The phone number is (323)728-5407. However they only cater to a minimum quantity of 4 per jet.

Some of the sub measurements may be hard to find: for example, 62.5 rather than 60 or 65. Currently, one place that still sells the full range is Jets R US

Why

The GS500, GS500E and GS500F are known to be jetted on the 'lean' side to improve fuel consumption and exhaust emissions. This is not optimal for best performance (ie. acceleration, power, torque, faster warm-ups, engine cooling and engine efficiency). A lean engine is one whose combustion has more air than the perfect air/fuel ratio.

In 2001 the GS500 carburetors changed to a new design that features three jets.

The stock jets for the GS500 are:
1989 - 2000: Pilot 40 (37.5 USA), Main 122.5 (yup, only two!)
2001 - 2003: Pilot 17.5, Mid Main 60, Main 127.5
2004 - 2007: Pilot 17.5, Mid Main 60, Main 130

There are four things to adjust your air fuel mixture. The pilot jet and idle screw affect the mixture at idle. Adding washers to the needle jet affects the mixture at partial throttle. The main jet affects the mixture at or near full throttle. Larger jets, or more washers on the needle jet, will make your bike run richer within the corresponding throttle range.

2001 - 2007 Carburetors

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

YEAR + Jet Size
2001+ Stock - 17.5 Pilots / 60 Mid Main / 127.5 Main
2004+ Stock - 17.5 Pilots / 60 Mid Main / 130.0 Main

These bikes use Mikuni Carburetors / Jets with the following part numbers for their jets:
Pilots = N224.103 or VM28/486 (apparently they are the same)
Mid Main & Main = N102.221

To what degree

A conservative Starting Point for upgraded Jetting (Pilots/Mid Main/Main) for a:
Stock GS500 = 20/60/135
Drop in K&N Air Filter Only = 20/62.5/140
K&N Pod or Lunchbox Air Filter Only = 20/65/142.5
Drop in K&N Air Filter + Sports Exhaust = 20/62.5/142.5
K&N Pod or Lunchbox Air Filter + Sports Exhaust = 20/65/145

Unfortunately Re-Jetting is a black art (so many variables including humidity, altitude, engine condition etc etc) so often much tweaking of jet sizes is needed to find the perfect combination.

See the Matrix for what other users have found to work.
Remember: The GS500 has two carburetors so you will require two of each jets!


You can also see the matrix with easy data entry at http://beergarage.com/GSMatrix.aspx


A thread here also lists members Jetting and Upgrade information http://gstwins.com/gsboard/index.php?topic=35237


89-2000
Air Filter / Exhaust Stock Air Filter UniF Dropin K&N Dropin UniF Pods K&N Pods K&N Lunchbox

Stock Exhaust

pilot 40
main 125
washers 1
turns 3
perfect
people 2

pilot 40
main 125
washers 1
turns 3

pilot 40
main 127.5
washers 2
turns 3

pilot 40
main 147.5
washers 2
turns 2.5
perfect
people 1

pilot 40
main 140
washers 1
turns 2.5
people 2

Stock Exhaust

Same as above
but 127.5 main
people 1
perfect

Cobra

pilot 20
main 150
washers 1
turns 3
people 1

Performance

pilot 40
main 140-150
washers 2-3
turns 3-3.5
people 2

pilot 40
main 150
washers 1
turns 3
people 1

Vance & Hines full

pilot 40
main 127.5
washers 2
turns 3
slightly rich
people 1

pilot 40
main 150
washers 1
turns 3

Vance & Hines slipon

pilot 40
main 150
washers 2
turns 3
perfect / lean at idle
people 2

SV650 slipon

pilot 40
main 135
washers 1
turns 3

ZX11 Yosh Slipon

pilot 40
main 147.5
washers 1
turns 3
elevation: 900'

2001+
Air Filter / Exhaust Stock Air Filter UniF Dropin K&N Dropin UniF Pods K&N Pods K&N Lunchbox
Stock Exhaust

pilot stock
mid stock
main stock
washers 2
turns 3+
slightly lean
people 1

pilot 20
mid 62.5
main 137.5
people 1

pilot 20
main 142.5
washers 1
turns 3
people 1

pilot 20
mid-main 62.5 or 65
with no washers
main 142.5
washers 2
turns 3
people 2
excellent performance, but
62.5 mid needed both washers

Performance Exhaust

pilot 22.5
main 127.5
washers 2
turns 2.5
slightly rich
people 1

pilot 20
mid 62.5
main 142.5
people 1

pilot 22.5
mid 65
main 147.5-150
people 1

pilot 22.5
mid-main 65
main 147.5
washers 3 (M3/3 mm, not #4)
turns out 2.5
full Jardine exhaust
FINALLY... took EIGHT tries to pefect, but it was worth it. Sweet.
people 1
pilot 20
mid-main 65
main 145
nothing else in the carbs touched
people 1

full aftermarket other

elevation 300'
pilot 17.5
mid 30
main 132.5
washers - clip 4/5
turns 3
people 1

Same info in original table format.

89-00

ExhaustAir FilterPilotMain#4 Washers or Clip PositionPilot Screw TurnsNotePeople
StockStock4012513p1
StockUniF(s)4012513  
StockK&N(s)40127.523  
StockUniF(p)40     
StockK&N(p)40147.522.5p1
StockK&N(lb)40???  
PerfStock40     
PerfUniF(s)40     
PerfK&N(s)40     
PerfUniF(p)40     
PerfK&N(p)40140 - 15023 - 3.5 1
PerfK&N(p)40140 - 150K&N@33 - 3.5 1
V&H(f)UniF(s)40127.523sr1
SV650(s)UniF(p)4013513 1
V&H(s)K&N(p)4015023p,lean at idle2

>00

ExhaustAir FilterPilotMidMain#4Washers or Clip PositionPilot Fuel Screw TurnsNotePeople
stockstockstockstockstock23+sl1
stockstock20stockstock   1
stockK&N(s)2062.5137   1
stockK&N(p)20 142.513 1
StockK&N(lb)20????  
Cobra(s)K&N(p)20 15013 1
PerfK&N(s)2062.5142   1
PerfUni(s)22.5 127.5Factory@22.5sr1
PerfK&N(p)2265147-50   1
PerfK&N(lb)2065145  p1

Air Filter: (s) - Stock Air Box, (p) - Pod replacement for Stock Air Box (lb) lunchbox

Note: r- rich, sr - slightly rich, p - perfect, l - lean, sl - slightly lean

-Courtesy of Mike

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Page last modified on September 09, 2012, at 03:37 AM