Re-jetting

[iclrag]

So far i havent found any step-by-step instructions on re-jetting, this is the best i've found so far http://gstwin.com/carb_work.htm
does anybody have any info to add? i've never worked on a carb like this before and i plan to buy jets as soon as i get paid this friday (i can finally install my new exhaust!!!!

[msforever]

But why do you have to rejeting? The whole carb will have to come out I am guessing....sounds like a lot of work man, good luck!

[iclrag]

I got a quote from the local biker mechanic at about $150 on the high end, thats installation and tuning, i thought that was a bit high so i'm thinking i'll do it myself

[iclrag]

But why do you have to rejeting? The whole carb will have to come out I am guessing....sounds like a lot of work man, good luck!

When you put a new exhaust and / or high intake air system you have to re-jet or the bike will run like crap!

[adidasguy]

#5141

I've  always wondered why rejetting is touted as necessary for changing the exhaust. I see it for changing the air box - as air/fuel ratios are critical for what goes into the engine.

The exhaust is what comes out after it is mixed and burned. At that point, its well.... exhaust! It is after it is burned.Only thing that would be different would be a little back pressure on the exhaust side of things.

I've changed exhausts on 3 bikes. No rejetting. Didn't notice any difference at all. maybe someone can explain the real physics behind the need to rejet when changing the exhaust - not just that "you need to do it because people say you should".

[RossLH]

Under the assumption that an aftermarket exhaust system scavenges exhaust better than the stock system, the result is improved volumetric efficiency. Volumetric efficiency is a measure of the engine's ability to fill its volume during the intake stroke. More volumetric efficiency means more air, more air means more fuel. Seeing as to how GS500's tend to run a little lean from the factory, it is safe to assume that the stock jets wont keep up with the increased flow.

That's the simplified version, but keep in mind it is based on a series of assumptions.

[fraze11]

#5141

I've  always wondered why rejetting is touted as necessary for changing the exhaust. I see it for changing the air box - as air/fuel ratios are critical for what goes into the engine.

I've changed exhausts on 3 bikes. No rejetting. Didn't notice any difference at all. maybe someone can explain the real physics behind the need to rejet when changing the exhaust - not just that "you need to do it because people say you should".

I hear you.  I put my yoshi on my 09 and ran it for ~3 months before jetting and it ran absolutely fine, in fact I think it ran better and my plugs were fine no issues at all.  The ONLY reason I jetted was because I changed the air box with K&N.  Had I not done that I would have NEVER jetted, it was fine.  I've always told anyone who's asked me, if you are just slapping on a slip-on and doing nothing else, run it for a bit before going into "rejet panic".  I'm sure I'll be flamed but whatever.  I think its a variable induced concern aside from modifications ie: year of bike, condition, geographical location, weather conditions etc etc

[adidasguy]

#5145

Agreed. So iclrag - go put on that exhaust. Re-jet later.

I think more bikes are screwed up by people opening up things they shouldn't touch. The only reason I opened up Trey's carbs is because he was running really bad (ended up being a flaky spark  plug). So in that I  opened them up, cleaned them and replaced the pilots while I was in there. Ended up taking 3 times to get it working right (the carbs).

When I do want to try rejetting again, I have extra sets of carbs so I can rejet them and leave the originals intact. If it gets screwed up,just swap the originals back on.

(I hate down time on a bike which might be why I have so many spare parts.)

[jestercinti]

I hear you Adidas. My bike was down for a week due to a flat tire. Started a secondary bike fund for when this happens again. Thinking of a lightweight 2 stroke enduro from 70s like a Yamaha or a Suzuki TS/TC type model.

Iclrag, I would see how the bike runs without jetting. Always been told that a loose exhaust header or different setup will lean out mixture. Been wrong in past so who knows.

[msforever]

But why do you have to rejeting? The whole carb will have to come out I am guessing....sounds like a lot of work man, good luck!

When you put a new exhaust and / or high intake air system you have to re-jet or the bike will run like crap!

I hear you man. I just put a K&N air box in my 04 500F (no mods) without re-jetting. Because per the instruction from K&N I should be fine by using the air flow restrictor, which reduce the air flow a lot I guess. It is only been a few days and I did not ride too much because it has been over 100 everyday in Chicago area...I am waiting for a cooler day to get the oil changed than I am ready to go! I will try how it runs and report back to you guys!

[iclrag]

Okay, maybe i won't re-jet immediately, but i do want to take the restrictor off my K&N intake system  that's the main reason for re-jet

[adidasguy]

#5147

Leave the restrictor until you re-jet.
Put the exhaust on NOW! Post pictures in an hour after you finish (unless you're watching Family Guy, Futurama or South Park... then you can take a little longer  )

[iclrag]

#5147

Leave the restrictor until you re-jet.
Put the exhaust on NOW! Post pictures in an hour after you finish (unless you're watching Family Guy, Futurama or South Park... then you can take a little longer  )

I still need a saw, but i can probably get my hands on a good one this weekend though 

[RossLH]

(unless you're watching Family Guy, Futurama or South Park... then you can take a little longer  )

Or Archer or Its Always Sunny In Philadelphia.

[iclrag]

(unless you're watching Family Guy, Futurama or South Park... then you can take a little longer  )

Or Archer or Its Always Sunny In Philadelphia.

What about Scrubs or Psych or burn notice or perhaps the glades? 

[BockinBboy]

(unless you're watching Family Guy, Futurama or South Park... then you can take a little longer  )

Or Archer or Its Always Sunny In Philadelphia.

What about Scrubs or Psych or burn notice or perhaps the glades? 

Or how about: Forget TV and get out there and ride! That's the only excuse for not giving immediate updates and pics! 

- Bboy

[iclrag]

(unless you're watching Family Guy, Futurama or South Park... then you can take a little longer  )

Or Archer or Its Always Sunny In Philadelphia.

What about Scrubs or Psych or burn notice or perhaps the glades? 

Or how about: Forget TV and get out there and ride! That's the only excuse for not giving immediate updates and pics! 

- Bboy

I thoght not having a saw was my excuse? haha hopefully done this weekend!

i just found a new smiley

[iclrag]

So, anybody know what typea of jets these use? Big small round? On a side note, the iduot at the shop gave me 120 not 20 pilots

[jestercinti]

Depends on the year.  Good reading here:

http://wiki.gstwins.com/index.php?n=Upgrades.Rejetting

[DoD#i]

I thoght not having a saw was my excuse? haha hopefully done this weekend!

Trade your TV for a saw. Have more time to ride.