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

Exhaust	Air Filter	Pilot	Main	#4 Washers or Clip Position	Pilot Screw Turns	Note	People
Stock	Stock	40	125	1	3	p	1
Stock	UniF(s)	40	125	1	3
Stock	K&N(s)	40	127.5	2	3
Stock	UniF(p)	40
Stock	K&N(p)	40	147.5	2	2.5	p	1
Stock	K&N(lb)	40	?	?	?
Perf	Stock	40
Perf	UniF(s)	40
Perf	K&N(s)	40
Perf	UniF(p)	40
Perf	K&N(p)	40	140 - 150	2	3 - 3.5		1
Perf	K&N(p)	40	140 - 150	K&N@3	3 - 3.5		1
V&H(f)	UniF(s)	40	127.5	2	3	sr	1
SV650(s)	UniF(p)	40	135	1	3		1
V&H(s)	K&N(p)	40	150	2	3	p,lean at idle	2

>00

Exhaust	Air Filter	Pilot	Mid	Main	#4Washers or Clip Position	Pilot Fuel Screw Turns	Note	People
stock	stock	stock	stock	stock	2	3+	sl	1
stock	stock	20	stock	stock				1
stock	K&N(s)	20	62.5	137				1
stock	K&N(p)	20		142.5	1	3		1
Stock	K&N(lb)	20	?	?	?	?
Cobra(s)	K&N(p)	20		150	1	3		1
Perf	K&N(s)	20	62.5	142				1
Perf	Uni(s)	22.5		127.5	Factory@2	2.5	sr	1
Perf	K&N(p)	22	65	147-50				1
Perf	K&N(lb)	20	65	145			p	1

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