Rejetting

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 ones who's 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
2001 - 2003: Pilot 17.5, Mid Main 60, Main 127.5
2004 - 2007: Pilot 17.5, Mid Main 60, Main 130

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. 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 and would redirect you to www.motorcyclecarbs.com, www.bikebandit.com, or your local dealer. As of November 2008, pre-2001 main jets are available for $3 at Chaparral Racing.

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

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. Please remember that we all blindly use 150 jets, knocking our performance down to a range us tards can handle.

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.

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
Mid Main & Main = N102.221

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!

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

Same info in original table format.

89-00

>00

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