Lunchbox and Jetting, Quick questions!

[Jayke]

Heya guys, this weekend I'm tearing my bike apart and fixing everything that needs doing. Since I'm going to be tearing the bike apart pretty much as I'm going to be doing the valves and such, I decided to go ahead and order a K&N lunchbox while I'm at it and rejet the bike. As of right now, the bike is on stock jetting running a motad system (but will be changing this to a Delkevic system in a months time, which said no rejetting will be needed).

UK GS500K1!

SO.... I'm in need of a carb gurus help here, the stock jetting on this bike is... following the Haynes...

Pilot Jet = 17.5

Pilot Air Jet = 165

Jet Needle = 5DH41

Main Jet = 115

Main Air Jet = 0.5mm

Starter Jet = 42.5

So going from these, which it will be as the bike is running lean like all the other stock bikes out there, what jets would I change and to which size?

----Im changing from the stock airbox to a K&N RU2970 Lunchbox. Motad system currently on, which I've read needs no rejetting.

Im assuming the only ones that will need to be changed will be the pilot jet, main jet and the starter jet, right?

With the carb questions out of the way, as I'm changing to a Lunchbox, I need a breather.... And I've been on a ton of different threads and not come to a conclusion as of yet.

Will this breather be fine, or will I need a different one (needs to be from UK)? http://www.ebay.co.uk/itm/NEW-Breather-Filter-10mm-Oil-Crankcase-Air-Small-R-/350860288605?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item51b0e7225d

And do I have to buy any hose to put the breather on? Or is the hose already attached to the engine/carbs (I assume it is, just want to be sure as I'm buying everything online and don't want to be caught out missing something!!)


Thanks alot for your help in advance, this forum has been a godsend as I'm new to all this!
Jayke.

[radodrill]

The Suzuki service manual doesn't list the stock mid-main jet, but this is probably a 60 (rather than the 42.5 you have listed from the Haynes manual).

With the stock exhaust and K&N drop-in filter, I jetted to 20/60/142.5 2.5 turns and that was amazing.  This is close to what's recommended for pods and a stock exhaust.

I have since added a Vance&Hines can on a set of stock headers and am still working on the ideal jetting.  Currently I'm running 22.5/62.5/147.5 and she's still lean on the idle (mixture screws 4 turns out) and probably lean overall as I still haven't had a loss in pull by stepping up the mains.  A buddy works at the parts counter at the dealership and he's going to help me exchange new jets for bigger.  At the very least I'll need a 25 pilot, but a 27.5 may be a safer bet.  That and I may need to bump the mid-main up to a 65.

[Jayke]

The Suzuki service manual doesn't list the stock mid-main jet, but this is probably a 60 (rather than the 42.5 you have listed from the Haynes manual).

With the stock exhaust and K&N drop-in filter, I jetted to 20/60/142.5 2.5 turns and that was amazing.  This is close to what's recommended for pods and a stock exhaust.

I have since added a Vance&Hines can on a set of stock headers and am still working on the ideal jetting.  Currently I'm running 22.5/62.5/147.5 and she's still lean on the idle (mixture screws 4 turns out) and probably lean overall as I still haven't had a loss in pull by stepping up the mains.  A buddy works at the parts counter at the dealership and he's going to help me exchange new jets for bigger.  At the very least I'll need a 25 pilot, but a 27.5 may be a safer bet.  That and I may need to bump the mid-main up to a 65.

Well I have a motad exhaust atm, going to this http://www.ebay.co.uk/itm/Suzuki-GS500E-F-89-02-350mm-Oval-Stainless-Steel-Silencers-Exhaust-Kit-/271214616592?pt=UK_Motorcycle_Parts_13&hash=item3f25a6a010

So do you think itll be worth getting the 25 pilot for myself? Looking to hopefully just do this once as I'm not so comfortable doing it alot .

And are those jets for a UK model K1? I assume itll be fine but it seems a huge jump, though you are the knowledgeable one, I'm a total noob!

Oh by the way, what do you think about the breather?

Thanks alot!!

[radodrill]

Well I have a motad exhaust atm, going to this http://www.ebay.co.uk/itm/Suzuki-GS500E-F-89-02-350mm-Oval-Stainless-Steel-Silencers-Exhaust-Kit-/271214616592?pt=UK_Motorcycle_Parts_13&hash=item3f25a6a010

So do you think itll be worth getting the 25 pilot for myself? Looking to hopefully just do this once as I'm not so comfortable doing it alot .

And are those jets for a UK model K1? I assume itll be fine but it seems a huge jump, though you are the knowledgeable one, I'm a total noob!

Oh by the way, what do you think about the breather?

Thanks alot!!

It all depends on how restrictive your new exhaust is.

The main difference between the UK vs US bikes is that the UK are jetted even leaner for emissions; though they do have a slightly different needle as well.  It looks the EU spec is a 130 or 135 main using the same needle as the UK just with the e-clip at the 3rd position rather than 2nd (I'm guessing higher in the UK).

In my case the stock jets were 17.5/60/130 and for just a drop-in I went up 5 sizes on the main and 1 on the pilot.  With the new (much less restrictive) exhaust even the 22.5 pilot is too lean; so at least a 25 is in order.

Depending on your new exhaust (not sure how the Delkevic can compares to stock or V&H), I'd say you'll need at least a 22.5 pilot.  With the stock 60 mid-main and new exhaust mine was very sluggish, the 62.5 solved that; so you may need the 62.5 as well.

For the main, it depends a bit on your location as well as the exhaust/intake.  I'd say that 142.5 would be a good start, but you may need bigger.


BTW, I can actually pull the carbs to change jets and have it back together in under 45min.

And there's a breather tube attached to the top end of the engine; you can put a filter on it but it's not mandatory as it's an outlet.

Edit: I'm guessing that the needle is lower on the UK speck (115 main); if the needles were at the same position, at WOT you'd feel a huge jump in power passing through 6-7K RPM with the 130 main (or a flat top end on the UK spec).  The difference in the needle height smooths out the transition regions (at WOT) from the mid to high range.

[Jayke]

Well I have a motad exhaust atm, going to this http://www.ebay.co.uk/itm/Suzuki-GS500E-F-89-02-350mm-Oval-Stainless-Steel-Silencers-Exhaust-Kit-/271214616592?pt=UK_Motorcycle_Parts_13&hash=item3f25a6a010

So do you think itll be worth getting the 25 pilot for myself? Looking to hopefully just do this once as I'm not so comfortable doing it alot .

And are those jets for a UK model K1? I assume itll be fine but it seems a huge jump, though you are the knowledgeable one, I'm a total noob!

Oh by the way, what do you think about the breather?

Thanks alot!!

It all depends on how restrictive your new exhaust is.

The main difference between the UK vs US bikes is that the UK are jetted even leaner for emissions; though they do have a slightly different needle as well.  It looks the EU spec is a 130 or 135 main using the same needle as the UK just with the e-clip at the 3rd position rather than 2nd (I'm guessing higher in the UK).

In my case the stock jets were 17.5/60/130 and for just a drop-in I went up 5 sizes on the main and 1 on the pilot.  With the new (much less restrictive) exhaust even the 22.5 pilot is too lean; so at least a 25 is in order.

Depending on your new exhaust (not sure how the Delkevic can compares to stock or V&H), I'd say you'll need at least a 22.5 pilot.  With the stock 60 mid-main and new exhaust mine was very sluggish, the 62.5 solved that; so you may need the 62.5 as well.

For the main, it depends a bit on your location as well as the exhaust/intake.  I'd say that 142.5 would be a good start, but you may need bigger.


BTW, I can actually pull the carbs to change jets and have it back together in under 45min.

And there's a breather tube attached to the top end of the engine; you can put a filter on it but it's not mandatory as it's an outlet.

Well the delk wont be for a while at least, so if I follow your suggestions, since its a UK bike, itll be okay right? Since the needle is different.

As you see I'm not educated at all in carbs or bike mech at all really. Doing this work with my dad overseeing as he has a little knowledge in his years.

So confusing!   

As long as itll be okay then I'll go ahead and do it. And as for the needle, if I dont know what to do when it comes to it, I guess I'll pop up an image or something on the forums.

22.5/60/142.5 you reckon then?

[radodrill]

I was very happy with 20/60/142.5 while running the stock exhaust and K&N drop-in; since you already have a motad you should be fine with a 22.5 pilot.  When using the stock 60 mid-main, if it's sluggish to respond to throttle inputs, then step up to a 62.5  And the 142.5 main should run fine; even if it's a bit lean, you'll just be running a bit hotter and not have the max possible pull from the engine.

The needle is the only more confusing part of the matter since it is a slightly different model than the US spec.  The US spec only has one e-clip position; I'm guessing the European models have an adjustable e-clip, where in the EU it's set to match the geometry of the US needle.

TLDR alert

I personally did my jetting by seat of the pants feel; got a few main sizes and went from there.  Also, while you have the carbs off for the first jet swap, make sure the idle adjust knob is set such that the butterflies are held slightly open with about a 0.5-0.75 mm gap between the butterfly and throttle body.

What I did was first select the best main jet such that I get the hardest Wide Open Throttle (WOT) pull at over 7K RPM; i.e. cruise just over 7K then roll hard on the throttle.

Once the best main was set, I adjusted the needle height such that at WOT I got a smooth transition passing through 6-7K.  Cruise around 4-5K then roll on hard.  If you get a sudden jump in power/ around 7K then you have to raise the needle a bit; if you have a hole where power drops near 6K then picks back up, then you need to lower the needle.  Remember, you're after a smooth transition.

After that it's fine tuning the idle, transition on/off idle, and responsiveness to throttle changes.

The pilot jets and mixture screws are what govern most of the idle performance.  The pilot is the coarse adjust and the screws are the fine adjustment; 1.5 turn of the mixture screws is equivalent to changing the jet by 1 size, typically you want to be between 1.5-3 turns out (maybe up to about 3.5 turns).
If the idle circuit is slightly lean (with respect to the main jetting), you can get a loopy idle.  With a cold engine, a rich idle will make it hard to start at warm temperatures but easier when it's cold out (once the engine is warmed up it'll often run fine) and you'll see the opposite with a lean idle.  I try to adjust the idle so that it'll start right up and idle smoothly if it's been sitting near 61 F (16 C) or so (approx garage temp); when it's been sitting in the cold I may need a bit of choke but not when it's warm out.

The on/off idle behavior is governed by the idle adjust knob and mid-main jet.  You can set the idle first as changes to the mid-main would generally only need minor adjustment to the mixture screws (pilots should be able to stay the same).
If your bike is sluggish to react to changes in the throttle, then your mid-main is too small.  Under no load (bike in neutral), you should be able to slightly twist the throttle and have it react almost instantaneously; with a sharp twist it should rev up rapidly.

In terms of on/off idle performance, while cruising around 4K RPM you want it to be smooth going from closed to slight throttle and back.  Use the idle adjust knob to set the idle around 1500 RPM (maybe slightly higher).  If you have a jump in power by going from idle to slight throttle, then need to turn in the idle adjust knob (holds the butterflies further open); if this in turn results in a very high idle (above 2K RPM), then you'll need to decrease the size of the mid-main.

I know this might seem complicated at first, but once you start you'll get a feel for it and it won't be too hard.

[Jayke]

I was very happy with 20/60/142.5 while running the stock exhaust and K&N drop-in; since you already have a motad you should be fine with a 22.5 pilot.  When using the stock 60 mid-main, if it's sluggish to respond to throttle inputs, then step up to a 62.5  And the 142.5 main should run fine; even if it's a bit lean, you'll just be running a bit hotter and not have the max possible pull from the engine.

The needle is the only more confusing part of the matter since it is a slightly different model than the US spec.  The US spec only has one e-clip position; I'm guessing the European models have an adjustable e-clip, where in the EU it's set to match the geometry of the US needle.

TLDR alert

Oh wow, definately going to bookmark this thread, feel like its going to help me alot in the near future

Right... I managed to find the main 142.5 jets, and the 22.5 pilot.... just having a HUGE trouble finding mid mains. I see from looking on the wiki, the jets are as follows:

Pilots = N224.103 or VM28/486 (apparently they are the same)
Mid Main & Main = N102.221

But I just cant find anywhere in the UK (online) that has the 60 mid main in stock!

I guess I'm just going to have to buy what I can online and go to my local bike shop and just pray that they have exactly what I need.

Pilots - http://www.ebay.co.uk/itm/291054962753
Mains - http://www.ebay.co.uk/itm/181007125391

Just those damn mid mains! Grrr....
Smallest I can find is like 100

[radodrill]

Oh wow, definately going to bookmark this thread, feel like its going to help me alot in the near future

I found a CV Carburetor tuning guide by FactoryPro online, yet that dealt with 2 jet carbs and didn't talk much about changing pilots.  The first few steps were spot on for selecting the main and adjusting the needle; from then on, it was trial and error tweaking to get it running great with the stock pipe.  With the new pipe, I first tried it with the jetting that I had with the stock pipe and found the sluggish behavior, which was resolved with 1 size larger mid-main.

So the guide I posted is part what I gleaned from FactoryPro and the rest (i.e. most of it) personal experience from trying various jets.

Right... I managed to find the main 142.5 jets, and the 22.5 pilot.... just having a HUGE trouble finding mid mains. I see from looking on the wiki, the jets are as follows:

Pilots = N224.103 or VM28/486 (apparently they are the same)
Mid Main & Main = N102.221

But I just cant find anywhere in the UK (online) that has the 60 mid main in stock!

I guess I'm just going to have to buy what I can online and go to my local bike shop and just pray that they have exactly what I need.

Pilots - http://www.ebay.co.uk/itm/291054962753
Mains - http://www.ebay.co.uk/itm/181007125391

Just those damn mid mains! Grrr....
Smallest I can find is like 100

Your bike should have a stock 60 mid-main; so you need to look for a 62.5  My local dealer actually had them in stock (just not all the pilots) and can order any jet; their prices were actually lower than buying online ($4-5 each vs $7+). 

Edit: here you go http://www.motocarb.co.uk/main%20jets.htm

[Jayke]

Thanks for that aswell, I will be (hopefully) doing all the work on it on Tuesday/Wednesday so it will all come useful and hopefully become a new bike!

Good call on the jets, though. I think I'll leave them for now and pop down my local shop and see what they have to say, can't hurt I guess!

Again, many thanks for the help and your patience, I'm sure I'll be back in a few days to rack your brain again lol!

Sent from my C6903 using Tapatalk

[radodrill]

not sure if you saw my edit; found a UK store that says they have basically all sizes of Mikuni small round jets from 50 up to 240;  looks like they only do phone orders, but their pricing is almost the same as the link you had to ABVracing's eBay store.  Note: they also sell the pilots.
http://www.motocarb.co.uk/main%20jets.htm

[Jayke]

not sure if you saw my edit; found a UK store that says they have basically all sizes of Mikuni small round jets from 50 up to 240;  looks like they only do phone orders, but their pricing is almost the same as the link you had to ABVracing's eBay store.  Note: they also sell the pilots.
http://www.motocarb.co.uk/main%20jets.htm

Didn't see it sorry - I'll give them a call tomorrow after I visit my local shop if they don't have any/the price is much better on motocarb. Motocarb will be costing me £22.40 (for all jets) which is about 38 dollars. Bet thats expensive to you, huh?

Thank you!

[radodrill]

Thanks for that aswell, I will be (hopefully) doing all the work on it on Tuesday/Wednesday so it will all come useful and hopefully become a new bike!

In my experience the difference is night and day.

When I got the bike with the stock jetting it seemed to be overly flat on the top end with the peak power band between 3-7K RPM; it also did not seem to have a hard pull and did not feel like it launched very well.  Further, it was easily capable of doing 95+ mph, but over ~60MPH the acceleration was not that great.  i.e. it felt very tame rather than like a sport bike.
After a rejet it became a totally different animal with a lot more torque to it and even required less choke to get it started on cooler days.  At any RPM I could roll on the throttle and feel the front end unloading and it also launches really well with a hard pull all the way up to the redline.  Higher speed acceleration is also very much improved; it would take maybe 0.5 sec to get from 70mph to 90mph.

My new exhaust has a lot more bark to it with a louder, throatier sound.  Even so it's now running on the lean side it still has the hard pull and good acceleration that the stock jetting lacked.

[Jayke]

My situation right now seems exactly the same as yours, like almost identical. Obviously it feels fast, but I've come from a 9hp 125cc and I have a big frame for a 125. The bike feels like it lacks alot of power between 2-4k. The main power would be 6.5k to 7.5k then after that it feels empty. Struggles after 80 kinda. I topped at 95, too. Didn't feel anything more in her. Wish I had the spare money to get it dyno 'd so I could see before and after.

Can't wait to see the difference

Sent from my C6903 using Tapatalk

[radodrill]

Motocarb will be costing me £22.40 (for all jets) which is about 38 dollars. Bet thats expensive to you, huh?

Thank you!

Comparable to prices online (e.g. jets-r-us), but about 30% more than my local dealer.

Either way it's by far cheaper than a dynojet kit (~$80US for the GS500 kit), which is utter crap.  I won't even bother elaborating, you'll get better results and spend less buying jets and tuning it yourself; even if you buy a lot of extra jets for testing various configurations you'll come out ahead.

My situation right now seems exactly the same as yours, like almost identical. Obviously it feels fast, but I've come from a 9hp 125cc and I have a big frame for a 125. The bike feels like it lacks alot of power between 2-4k. The main power would be 6.5k to 7.5k then after that it feels empty. Struggles after 80 kinda. I topped at 95, too. Didn't feel anything more in her. Wish I had the spare money to get it dyno 'd so I could see before and after.

Can't wait to see the difference

Sounds very similar to what mine was stock.  I'm sure it would have done maybe 110mph (at the time I didn't feel comfortable taking it faster than 95), yet at that speed the acceleration was uninspiring.

I might have been OK with it had it been my first bike; but coming from a 2007 Ninja 250 I was disappointed.  That ninjette loved the mid-high range; not much power under 4K, but hard pull from 4K up to the redline.  The biggest downfalls of the 250 are that it tops out ~90-95 (basically at redline; at ~80mph it was at 10.5K RPM), not great acceleration over 55-60 mph, and got buffetted a lot by the wind.

The stock GS didn't feel nearly as spirited; but the rejetted GS is way more fun than the 250 was.



I'd recommend getting a few additional jets so you can try what works best for you.  You probably won't get it perfect on the first attempt, but if you take the time to do it right (a few jet changes) then you'll definitely be very happy with the results.  The reason why I stress trying different jets is again due to experience; with the stock pipe a 140 main and 145 main have way less pull than the 142.5 (ideal) main.  My suggested jet sizes should be fairly close (at lease a great starting point), but you'll want to test for yourself that you have the best jets for your intake and exhaust.

[Crasm]

Im from the uk and just ordered my jets off motocarb.co.uk price was 24.50 including delivery
I have delkavic full system and k and n lunch box
Jets ive gone for are 20/65/147.5
Dont believe delkavic my bike was lean an f%$k with that
Straight through system on

[Jayke]

Interesting. May be the same case with motad, maybe thats why it's running so lean now. It has the motad system on and it's never been jetted as far as I know.

I will try the suggested jets, which I'm just about to go and buy(hopefully) or order. Then see how it is. Once I've had the bike apart once, I'll be fine with tearing it down. This is my first time when I do it soon so yeah! :p

Just out of curiosity,  which delkevic system did you go for? I'm looking at the 350mm one as that's road legal. I tried finding a good video but there was only one!

Sent from my C6903 using Tapatalk

[radodrill]

Once I've had the bike apart once, I'll be fine with tearing it down. This is my first time when I do it soon so yeah! :p

Most certainly the case; and with your new lunchbox it will be a lot easier (can stay attached to the carbs).  Also, the stock screws on the carbs are a pain to get out; best to replace them with stainless Allen screws; IIRT M4x.7 on the bottom and M5x.8 on top

[Jayke]

Yeah I've heard the stock airbox is a massive pain. Glad I'm getting rid of it lol! And oh right thank you, I will get some while I'm out!

Sent from my C6903 using Tapatalk

[BockinBboy]

Motad is full stainless, but UK noise restrictions limit the system a bit compared full systems like delkevic... Motad is approved for UK... I couldn't say for sure, but I doubt it would need same jetting as lunchbox with other full aftermarket exhausts like delkevic.  It would probably be close to it... and if you plan to get a delkevic, might as well get the jets for that known setup, but jetting needed for lunchbox and delkevic will be likely be richer on your lunchbox with motad.

- Bboy

[BockinBboy]

Motad is full stainless, but UK noise restrictions limit the system a bit compared full systems like delkevic... Motad is approved for UK... I couldn't say for sure, but I doubt it would need same jetting as lunchbox with other full aftermarket exhausts like delkevic.  It would probably be close to it... and if you plan to get a delkevic, might as well get the jets for that known setup, but jetting needed for lunchbox and delkevic will be likely be richer on your lunchbox with motad.

- Bboy

Edit: Also forgot to mention about the needles... UK is different particularly for pilot jet due to the needle... this is more unknown territory for me, but if 115 pilot were used on US needle - I'm not sure how well that would even run, if able to start (slight exaggeration, but making a point)... I'm just inferring that 22.5 pilot would probably be too rich for your UK needle...