I will definitely be playing around with different jets and such when I get paid.

I can make more videos tomorrow in the day, the throttle is fine for small and big changes so far from what I see. The response is almost instantaneous it feels. Everything seems good other than the flat spot which I was talking about. Need to find a way to get that damn screw out. May invest in an ez -out. Seems a great Idea, then I'll be able to change the needle and get some pics for the wiki!

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Quote from: Jayke on March 03, 2014, 09:45:40 PM
I will definitely be playing around with different jets and such when I get paid.

On the mains; if you go bigger and you have same or better WOT pull, then you're not to rich; if you lose some pull you've gone too rich.  The sweet spot is right where you get the peak amount of WOT pull.

And you if you're lean now, you'll probably also get more bark when you have the ideal tuning.

As I said before, with the stock pipe I went up to 20/60/142.5; with the new exhaust, she ran fine (no hesitation) with simply changing the mid-main to a 62.5, but she was running lean and at 22.5/62.5/147.5 she's still lean.  I'm about to step up to a 25 pilot and look at a 150 or 152.5 main.  Note: I'm still in the process of tuning for the new exhaust.  I wouldn't be surprised if the Delkevik would run more like a performance exhaust than the stock (particularly without the silencer).

I guess I'll take a few in different sizes and just do it like you say, after seeing the difference it's made so far, I can't wait to perfect it. Gonna order a load of jets to play around with, should be a busy month! :p

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Ill let u no how i get on with mine on Saturday
Im gunna do the buddhas recommended set up . My jets arrived today so im ready to go for the weekend
Hopefully itll be perfect if not it tweek it and report back

Great to hear! Can't wait to hear what you think, just been riding on some faster roads. My acceleration after 65 ish is really bad. Managed to get up to about 80 and it didn't feel like it wanted to go much more.

Will wait till Saturday to see what yours is like then will go from there

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Thats really bad!! You still having trouble with mid range??
I think your mid jet it 2 small and not moving your needles  is probs another reason .
Whats your spark plugs saying??

Keep in mind that the throttle position and RPM are way more important than land speed when tuning the carbs.

Quote from: Crasm on March 04, 2014, 11:00:51 AM
I think your mid jet it 2 small and not moving your needles  is probs another reason .

The main dominates at ~3/4+ throttle; the 2/4-3/4 range is governed by how far the needle is in the main, and <1/4 throttle is governed by the idle and starter circuits.

If you're lacking power (particularly at the top end with WOT) then you need to adjust the main.  You'll actually see a peak in pull (torque) with the optimal main and it drops of if you are too rich or too lean.
If at WOT you notice a flat spot or jump in power when passing through 5-7K, then you need to adjust the needles to (lower/raise) to lean/richen the mid-range mixture (with respect to the top end).  A flat spot indicates that the mid range is too rich and jump means that the mid-range is lean.
The mid-mains control the starter circuit and is best tuned on/off idle with very small changes in throttle input.  If you go from closed to slight throttle and feel a sudden pull, then your mid-main is too big.  If the bike hesitates or is slow to respond to throttle inputs, then your mid-main is too small.

The pilots and mixture screws are the coarse/fine adjustment of the idle behavior.  If the cold engine is very hard to start with low temperatures (even at full choke), then you're running lean on the idle; easy at low temp but hard at high temp is a rich idle.
The idle adjust knob simply sets the stop on the butterfly valves and thus the idle speed.

Radodrill - very interesting read thanks for that. I deffinatly have a better understanding of what  controls what in the carbs .
Im guessing ''WOT'' means working operating temperature??
So if i rip the throttle full open and it jumps in power delivery its lean and if it flats out its rich on the main jet??
Like wise with the mid main - so lowering the e clip raises the needle and makes the mixture richer??(in the mid range)
And highering the e clip lowes the needle and makes the mixture leaner?? (in the mid range)

Cheers for being patient and all the info you have provided its very much appreciated

WOT = Wide Open Throttle .... 

.. however in a general observation .. as to the title of this thread ... there ARE NO QUICK QUESTIONS regarding jetting .. ever!! 

Quote from: Crasm on March 04, 2014, 04:34:34 PM
Radodrill - very interesting read thanks for that. I deffinatly have a better understanding of what  controls what in the carbs .
Im guessing ''WOT'' means working operating temperature??
So if i rip the throttle full open and it jumps in power delivery its lean and if it flats out its rich on the main jet??
Like wise with the mid main - so lowering the e clip raises the needle and makes the mixture richer??(in the mid range)
And highering the e clip lowes the needle and makes the mixture leaner?? (in the mid range)

Cheers for being patient and all the info you have provided its very much appreciated

WOT = Wide Open Throttle

TLDR Alert

The GS uses CV (Continuous Velocity) carburetors  The following is tailored to our 3-jet carbs.

Essentially the throttle moves a set of butterfly valves that control the volumetric air flow rate into the engine.  The carb has a vacuum operated variable venturi, where a slide raises/lowers to maintain a constant air velocity through the venturi.  At the throat of the venturi is an emulsion tube to atomize the fuel flowing through the main jet.  The needles are attached to the slides and drop into the outlet port of the emulsion tube; so the amount of fuel metered depends on the size of the main, how much of the port is blocked, and how much of a vacuum is generated at the throat.

The mid-main aka starter jet feeds fuel to transition ports near the butterflies.  The fuel metered by these ports is not dependent on the slide or needle position, but is very sensitive to changes in the vacuum pressure (directly related to throttle position).  Thus the mid-main controls the responsiveness to changes in throttle inputs and compensates for the lag between throttle and slide movements.

The pilot jet feeds both the idle and choke circuits.  I won't really talk about the way the choke works as that doesn't affect the way the bike runs when fully warmed up (and the choke off).  Air is drawn into passages through the carbs and pass through the pilot jet's emulsion tube (integrated in the jet).  The resulting fuel mix goes to the mixture screws, which meter how much fuel is feed into the engine intake through ports in front of the butterflies.  The pilot and mixture screws control the low airflow behavior (closed throttle and starting the engine); generally speaking, 1.5 turns of the mixture screws is equivalent to 1 size difference on the pilot jet.

In the case of the 2-jet carbs, the pilot also feeds the transition ports; making them a bit more difficult to tune.


With that out of the way, you want to try to tune each aspect in turn.  It's best to start off with the main jet and tune everything else around that; so initially if the bike runs ignore poor idle or hesitation as that will be addressed later.

At >7K and WOT the slides will be fully raised and the main jet metering most of the fuel; so you want to adjust the mains to give you the hardest pull in that range.  Both lean and rich will result in less than ideal pull.  A lean state means hotter burn thus more wear on the engine; rich results in unburned fuel coming out with the exhaust, which can lead to soot at the tailpipe and or smoke coming out of the exhaust (smelly and blue smoke when overly rich).

With the main jet optimized, you can adjust the needle to tune the mid-range with respect to the top end; what you are looking for is smooth power delivery when transitioning from the mid range to the top end (part raised to fully raised slides).  Start at ~4K and give WOT; if you feel a jump in power passing through 6-7K you know the mid-range is lean and you have to raise the needles.  On the other hand, if you feel a flat spot or hole when passing through 6-7K, then the mid range is rich and you have to lower the needle.

Now adjust the pilot and mixture.  You want to turn down the idle adjust knob and increase the mixture till the RPMs climb and you reach a peak; then you can use the idle adjust knob to reach your desired idle speed.  Bear in mind that you want the mixture screws to be between 1.5 and 3 turns out (from lightly seated); if you have to go much beyond that range, then you have to swap the pilot jet.
Overly rich or lean idle states can be identified identified when trying to start a cold engine.  If the bike has been sitting in a low temperature environment (say <45F) and it is hard to start even at full choke you're running lean.  If it starts fine (often even without choke) at cold temperatures, but has trouble when it's warm out; then you're idle is too rich.
I generally try to set it up that I don't need choke when it's been sitting at ~ 55-60 F or above; then under 50F use some choke as necessary and she should start trouble-free (with full choke) even below freezing.

Finally adjust your mid-main to set your throttle responsiveness;  this you'll do based on making small changes in the throttle position.  Start with the bike in neutral (e.g. on the stand) and roll on the throttle both slow and fast; if it doesn't respond well to slow throttle changes or lags a lot with fast throttle change, then you have to up-size your mid-main.  Then test riding performance; cruise at 4K RPM and slight throttle, if it jerks going to/from closed throttle (drop/jump in power) your mid-main is too big.  Since you don't have any fine adjustment, you'll want to select the jet that doesn't lag yet minimizes the transitioning to/from closed throttle.

Note: After adjusting the mid-main, you might have to slightly adjust the mixture screws.

Quote from: Janx101 on March 04, 2014, 05:11:22 PM
.. however in a general observation .. as to the title of this thread ... there ARE NO QUICK QUESTIONS regarding jetting .. ever!! 

and as a result no short answers 

Legend!! Again thanks for the info very much appreciated
all this will come in handy for me at the weekend

Thanks again

Quote from: Crasm on March 05, 2014, 02:10:02 AM
Legend!! Again thanks for the info very much appreciated
all this will come in handy for me at the weekend

Thanks again

No problem.  As you can tell, once you get a feel for it you can tell what needs to be adjusted and address several aspects of the tuning at the same time.  For example, very lean idle, hesitating a lot, and lean throughout you know you'll need to step up all 3 jets; so you can change them all even while you're still figuring out the best main jet so you at least get the idle close and remove hesitations so that you can focus more on each detail.  In this example, you naturally want to come back and fine-tune everything after you found the best main.

So next question is ive gone for a 147.5 main what if that is to lean and say a 150 ia to rich what happens then??

If that were to occur, then you would need to raise the needle on the 147.5.

- Bboy

All I can say is wow! Rado you are one knowledgeable individual, I think I should just come over to the US and let you ride my bike, hahah.

I'm slowly learning. Done about 100 miles since the k &n and rejet. Noticing that the bulk of pull I feel like is 3-5.5k. Been rarely going over 7k though, this delkevic sounds so damn nice in the lower rev range!! Bottom end of revs, the front end actually lifted up a tad today when pulling off, so I think that end is good, top end the revs climb very slow compared to before the changes. Acceleration stops almost at 80 ish. Not sure if I told you this already I've been off past few days, my dog that we've had since 2001, passed away the other day, poor dog

Going to see if I can get the last screw off the top of the carb so I can do the needle possibly this weekend.

Again, thanks alot rado for all the info,  I'll need to read it again tonight to soak it all in, pretty mind taxing stuff!!

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Quote from: Crasm on March 05, 2014, 10:50:01 AM
So next question is ive gone for a 147.5 main what if that is to lean and say a 150 ia to rich what happens then??

Go with the jet that gives you the hardest pull.  More likely than not that scenario wouldn't occur, particularly with a performance exhaust.

Quote from: BockinBboy on March 05, 2014, 11:10:22 AM
If that were to occur, then you would need to raise the needle on the 147.5.

The needle tunes the part throttle with respect to the full throttle; if you raise the needle too much you get a hole or flat spot during the transition between 6-7K RPM, which is most noticeable at WOT

Quote from: Jayke on March 05, 2014, 11:11:59 AM
All I can say is wow! Rado you are one knowledgeable individual, I think I should just come over to the US and let you ride my bike, hahah.

Well it's just the Engineer in me.  Read a bit and play with things and it comes naturally

Quote from: Jayke on March 05, 2014, 11:11:59 AM
Not sure if I told you this already I've been off past few days, my dog that we've had since 2001, passed away the other day, poor dog

Sorry to hear about your dog; I bet you miss him a lot 

Quote from: Jayke on March 05, 2014, 11:11:59 AM
I'm slowly learning. Done about 100 miles since the k &n and rejet. Noticing that the bulk of pull I feel like is 3-5.5k. Been rarely going over 7k though, this delkevic sounds so damn nice in the lower rev range!! Bottom end of revs, the front end actually lifted up a tad today when pulling off, so I think that end is good, top end the revs climb very slow compared to before the changes. Acceleration stops almost at 80 ish.

Going to see if I can get the last screw off the top of the carb so I can do the needle possibly this weekend.

I often run mine up to the redline    At WOT you should easily feel a hard pull anywhere between 3-9K or so.  By the sound of it, your main is probably too small, but you may be close on the mid-main.

Quote from: Jayke on March 05, 2014, 11:11:59 AM
Again, thanks alot rado for all the info,  I'll need to read it again tonight to soak it all in, pretty mind taxing stuff!!

It's one thing to just read and try to understand it; once you start playing around with it it'll make a lot more sense

Im already starting to think about 150 main jets . . .

Quote from: radodrill on March 05, 2014, 12:08:37 PM

Quote from: BockinBboy on March 05, 2014, 11:10:22 AM
If that were to occur, then you would need to raise the needle on the 147.5.

The needle tunes the part throttle with respect to the full throttle; if you raise the needle too much you get a hole or flat spot during the transition between 6-7K RPM, which is most noticeable at WOT

LOL, there was a lot of hypothetical missing information there... Guess you put it better - Go with the jet that gives you the hardest pull.  But I would add to that - adjust the needle height to give you the best transition with that particular jetting. 

Before I rejetted mine - the stock setup would have OK acceleration on WOT, but everytime it hit just past 6k rpm, it would pull much harder, like slide me back in my seat harder.  Bad news if I wasn't paying attention, but otherwise particularly fun pulling through a good turn... Since I rejetted though, and adjusted needles a few times, it has a smooth acceleration all the way through - and much stronger 3-9k overall... without that surge at about 6k.

- Bboy