Jetting questions (not a GS, but close)

[t3rmin]

Ok, this is for my XS, but the GS forums are a little more advanced in this area than the XS forums...

Anyway this XS11 didn't come with an airbox, just four falling-apart UNI pods. I replaced those with some nicer K&N pods I had around. It's also got MAC 4-2 exhaust. Stock main is 137.5 and stock pilot is 42.5, needle in third position (middle). These are Mikuni BS CV carbs just like a GS.

Here's what I've tried:
Stock jetting: VERY lean, pipes turned very blue quickly. Flat spots in the power band, but I can't remember where. White plugs.

142.5 mains (2 sizes up) + stock pilots: Plugs pretty white still. Flat spots at 1/4 throttle and 3/4 throttle.

142.5 mains + 45 pilots (1 size up): Warms up better, otherwise pretty similar.

145 mains (three sizes up) + 45 pilots: Crisp response off the line, blubbering mid-range.

145 mains + 45 pilots, needle clip down 1 notch (needle raised): Still great 1/4 response, but big soggy area in the middle and WOT until RPMs are way up, then finally clears up close to redline.

145 mains + 45 pilots, needle clip bottom notch (needle at highest position): Soggy area has extended lower and higher. Midrange nonexistent. Can barely pull past to redline, where it just barely clears up.

142.5 mains + 45 pilots, needle clip still on bottom: Powerful off the line as usual. Slightly better midrange but still huge bog. Pulls harder at the very top.

142.5 mains + 45 pilots, needle clip 2nd from top (needle 1 step LOWER than stock): Midrange back, but stumble off the line. Slight flat spot in high end (transition to mains?). Pulls very well at the tippy-top.

And that's where I'm at right now. I *think* my next step should be to get some 140 mains (and probably get needle back to stock position). Obviously I got way too rich for a while, then when I moved the needle back down past stock (clip up), the bad spot kind of inverted, so I think it's compensating for too-big mains.

So based on my experience so far, I think this will be the correct setting:
140 mains + 45 pilots. Needle at stock position or up one (clip down) or maybe drill the slides a bit to get back that low-end grunt I was seeing when the needle was raised.

Seems like it wants to be pretty rich down low, but not up high. Maybe a result of the mismatch of high-flowing pods with near-stock exhaust?

Your thoughts?

 

[walt]

Don't drill the slides! Many 4 to 1's give a good boost in the midrange. The 140's or 142,5 mains should be fine. Can you find some #50 pilots? Or try raising the float level 1mm. Or try adding 1/2 turn out on the pilot screws. A smaller air by-pass jet can also help if the Yamaha BS's have the threaded style. Also check that all the plugs read the same. If you have not sync'ed the carbs, you should do that. Carbs not in balance will give a hesitation/dead spot in the lower midrange and at steady throttle the motor will surge. As well as to be slow to warm-up.

 

[Guest]

Don't they nake a DJ kit for the Yammy?

 

[t3rmin]

Sadly I can't find a DJ kit for anything but outrageous prices.

Why not drill the slides? My thought is since it seems to want to be fairly rich down low and leaner up high (relatively), drilling the slides would "slide" the enrichening range of the needle circuit down to lower revs/throttle openings. Doesn't eliminating the airbox generally retard slide action, so drilling is an effort to get 'em moving more like stock? As it is, the transition to mains doesn't seem to happen until you're at WOT *and* just shy of the redline (slides taking a while to catch up?).

When I had the needles up pretty high (clip down low) its off the line kick was fantastic, but it was way too rich in the middle. I'd hate to lose that instant throttle response and torquey low end.

 

[Guest]

Drill the slides with the K&Ns.

 

[t3rmin]

Drill the slides with the K&Ns.

Yes I think I will. I read on the XS forums to hit 'em with a 2.5 or 3mm bit. Sound about right?

Do ya think I'm on the right track with going to 140 mains?

 

[Guest]

From reading your post I'd start with the last settings with the slides drilled. Have the 140s ready to go and do plug chops.

With pods and the CV carbs the slides don't rise fast enough to compensate for all the extra air flow from the pods. By drilling the slides you will lift the slide (needle jet) quicker and compensate for the extra air. I went to the Dynojet site and the drill bit they use is a #32. (Whatever that means) But I would ASSUME a 3.2mm.

 

[walt]

A #32 drill is a number drill whose diameter is .1160" For reference a 2.5mm drill is .0984" and a 3.0mm drill is .1181". Also 3.2mm is .1260"

 

[t3rmin]

Sounds like #32 would be just about right then. Thanks guys.

*edit* Actually looks like the DJ Kit for the XS1100 comes with a #39 bit (about 2.5mm), so maybe I should start there. Although that's for the '80+ models, which had some carb changes. But better to start small since you can always go bigger. ;-)

 

[t3rmin]

Update:

Drilled the slides with the #32 bit (was too impatient to try #39 first). Low end might be slightly better, but midrange is blubbery (rich) again. So I definitely need to go down on the mains. I'm almost thinking I should drop in the 137.5's (stock size).

And to get back the low end the needle is definitely going to have to come up (clip down) -- quickening the slide action with drilling wasn't enough. I wonder if I'm going to have to epoxy and re-drill those slide holes smaller, since my feeling is the duration of the needle circuit needs to be spread out. But I'll try the mains first.

 

[Guest]

How's it pulling at full throttle? That would determine the main. Sounds like you need to lean the needle. (lower) by raising the clip.

I have done the epoxy and redrill and it works out fine. I used JB Weld.

Do a search for plug chops.


[SIZE=+1]Follow steps in order....[/SIZE]First[SIZE=+1], dial in:[/SIZE]

• [SIZE=+1]1. Top end (full throttle / 7.5k to redline -[/SIZE]
  Best Main Jet must be selected before starting step 2 (needle height)!
  • • [SIZE=+1]Select Best Main Jet [/SIZE]
  • To get the best, most even top end power (full throttle/after 7500 rpm), select the main jet that produces the hardest pull at high rpm.
    • If the bike pulls harder at high rpm when cold and less hard when fully warmed up, the main jet is too large. Install a smaller main jet and retest until you find the main jet that pulls the hardest at high rpm when fully warmed up. This must be done first - before moving on to the other tuning ranges.

• • • If the bike doesn't pull well at high rpm when cold and gets only slightly better when fully warmed up, the main jet is too small.
      • In order to properly tune the midrange and low rpm carburetion, THE MAIN JET MUST FIRST BE PROPERLY SELECTED after 10 to 15 minutes of hard use!
        • Do not pay too much attention to the low-end richness when you are changing main jets - you still need to be using the main jets that produce the best power at high rpm. You will deal with the low-end / cruise later - after step 2.
• [SIZE=+1]2. Midrange (full throttle /5k-7k)[/SIZE]
  Step 1 (Best Main Jet) must be selected before starting step 2!
  • • [SIZE=+1]Select best needle clip position[/SIZE]
  • To get the best power at full throttle / 5k-7k rpm, adjust the needle height, after you have already selected the best main jet.
    • If the engine pulls better or is smoother at full throttle/5k-7k in a full throttle roll-on starting at <3k when cool but soft and/or rough when at full operating temperature, it is too rich in the midrange and the needle should be lowered.
    • If the engine pulls better when fully warmed up but still not great between 5k-7k, try raising the needle to richen 5k-7k.
    • If the engine pulls equally well between 5k-7k when cooler as compared to fully warmed up, the needle height is probably properly set.
      • Do not pay too much attention to the low-end richness when you are changing needle clip positions - you still need to be using the clip position that produces the best full throttle / 5k-7k power in conjunction with the main jets (Step 1) that produce the best power at high rpm. You will deal with the low-end / cruise next.

• [SIZE=+1]3. Low end (full throttle / 2k-3k)[/SIZE]
  Step 1 (Best Main Jet) and Step 2 (needle height) must be selected before starting step 3!
  • • [SIZE=+1]Float height (AKA fuel level & how to..)[/SIZE]
  • To get best low-end power, set float height (fuel level) so that the engine will accept full throttle, without missing or stumbling, in 2nd gear from 2.5k to 3k rpm at minimum.
    • Float heights, unless otherwise specified in the installation guide, are measured from the "gasket surface" of the carb body to the highest part of the top of the float - with the float tang touching but not compressing the float valve spring.
    • If the engine has a "wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that gets worse as the engine heats up, lower the fuel level by resetting the float height 1mm greater (if the original was 13mm - go to 14mm). This will lower the fuel level, making full throttle / 2k-3k rpm leaner.
    • If the engine is "dry" and flat between 2k to 3k rpm, raise the fuel level.
    • Example: change float height from 15mm to 14mm to richen up that area.

• • • REMEMBER, since the main jet WILL affect low speed operation, the MAIN JET has to be within 1 or 2 sizes of correct before final float setting.
      • Warning: If the engine is left with the fuel level too high,, the engine may foul plugs on the street and will be "soft" and boggy at part throttle operation. Adjust Floats to raise/ lower the Fuel Level.
        • Base settings are usually given if a particular application has a history of fuel level criticalness. The Fuel level height in the float bowl affects full throttle/low rpm and, also, richness or leanness at cruise/low rpm.
      • Reference: a bike that runs cleanly at small throttle openings when cold, but starts to show signs of richness as it heats up to full operating temperature, will usually be leaned out enough to be correct if the fuel level is LOWERED 1mm. Check out and RESET all: Suzuki (all), Yamaha (all) and Kawasaki (if low speed problems occur). Needless to say, FUEL LEVEL IS EXTREMELY IMPORTANT!!!
    • If there are low-end richness problems, even after lowering the fuel level much more than 1.5mm from our initial settings, check for needle wear and needle jet (part of the emulsion tube). See Worn Needle and Worn Needle Jet diagram. It is VERY common for the brass needle jets (in the top of the "emulsion tube") in 36mm, 38mm and 40mm Mikuni CV carbs to wear out in as little as 5,000 miles. Check them for "oblong" wear - the needle jet orifice starts out round! Factory Pro produces stock replacement needle jets / emulsion tubes for 36mm and 38mm Mikuni carbs. Click here
• [SIZE=+1]4. Idle and low rpm cruise[/SIZE]
  • • [SIZE=+1]Fuel Screw setting (AKA mixture screws)[/SIZE]
      • There is usually a machined brass or aluminum cap over the fuel screws on all but newer Honda. It's about the diameter of a pencil. Cap removal details. Newer Honda carbs have no caps, but use a special "D" shaped driver, usually supplied in the carb recal kit. We do have them available separately, too. 800 869-0497 to order -
    • Set for smoothest idle and 2nd gear, 4k rpm, steady state cruise operation. Set mixture screws at recommended settings, as a starting point. For smoothest idle, 2nd gear 4000 rpm steady state cruise , and 1/8 throttle high rpm operation. (pj tuning information)
    • Pilot fuel mixture screw settings, float level (but, you've "fixed" the fuel level in Step 3 - which you have already done!) AND pilot jet size are the primary sources of mixture delivery during 4000 rpm steady state cruise operation.
      • If lean surging is encountered, richen mixture screws (turn out) in 1/2 turn increments. Alternative pilot jets are supplied when normally required.
      • Pilot fuel mixture screw settings, float level and pilot jet size also affect high-rpm, 0 to 1/8 throttle maneuvers. Too lean, will cause surging problems when the engine is operated at high rpm at small throttle openings! Opening the mixture screws and/or increasing pilot jet size will usually cure the problem.
        • NOTE: A rich problem gets worse as the engine heats up.
          • If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.
        • NOTE: A lean problem gets better as the engine heats up.
          • If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm!

 

[KEITH KRAUSE]

Are you sure the stock mains are 137.5?? Seems wrong but if that's correct the K&N pods will require a minimum 3 FULL sizes (15) larger in my opinion, maybe more. 4 full sizes (20) is more typical actually.
Then IF that Mac is flowing better than stock, 1 full size up (5) is usually the minimum and 2 full sizes (10) is typically the max needed.
Combine the two and you have a range of 20 to 30 (35 in some cases)increase above whatever is the factory main. I'd probably try a 162.5 in your case but I question your stock main info.
As always, test the main at full throttle only.
Can't say about the jet needle position without knowing what a solid 1/3 to 1/2 throttle chop test revealed. You obviously have adjustable needles. If a DJ needle, position 4 from the top is a very commonly used position on your model. Some say position 5 was the sweet spot, or position "4 1/2" by using a standard jetting spacer.
1 full size up is typical for the pilot jet. Adjust mixture screws using the highest rpm method to fine tune each cylinder.
Air jet may have to be increased too.
Dilling out the vacuum passage to the diaphragm/piston chamber improves any throttle response issues.
A good carb synch is necessary to accurately re-jet. Ignition advance timing and valve clearances must be spot on before synching.
REMOVE the 2 floatbowl vent line to eliminate any chance of float bowl venting issues.
Carbs must be clean and no intake leaks. Floats adjusted.
Be very careful of oiling the K&N's too much. Very easy to do.

 

[t3rmin]

So far it feels like the thing pulls hardest on the main jet with the 142.5's.

Plug chops with the 145's and lowered needle showed fluffy black rich (keeping it in the middle blubbery area).

Stock is definitely 137.5. I actually put those back in as an experiment and put the needle back to middle position. That means the changes from stock are: +1 size pilot jet and drilled slides to ~3mm. Power band is smoother, just a touch of the rich burble at the needle-main transistion. And since it's whimpy down low again, I think dropping the needle one notch (position 4) should richen it down low and bring back the snap, plus cause it to be open slightly sooner and maybe cure that high-mid richness. Plugs are pretty lean, though, so it's definitely not the right main jet, just an experiment.

Anyway, that was my next move until a needle e-clip went sproinging across the garage and I had to call it a night. ;-)

Also I've got 140's on order now. Jetting guidelines from the XS folks are: +3 for pods, +1 for 4-1 pipe, but "penalty" of -1 for mismatch of stock pipe + pods. Based on my experience so far I'm going to assume the MAC has similar flow to stock, so ballpark would be (3 - 1) +2 on the mains.

So the 142.5's should be close. I still haven't tried them after slide drilling with needle clip in 4th position.

 

[KEITH KRAUSE]

Hmmm. Not sure if you're testing each circuit at the appropriate throttle position. That will cause frustration if you do.
If you look around, there are a million jetting charts and recommendations for allowing this or that much change per mod, etc.
I've always tried to find out what the main jet choice(s) are in various jet kits and follow that as a guide. That usually works well and you get the main right within 2 attempts. The correct jet needle position for your bike can be a bit more varied but you usually get that right within 3 attempts. Pilot jet choices in the kits are almost always correct within 1/2 size. Same with the air jet.
I hope the bike was otherwise tuned and ready for the re-jet.
I won't argue with you but I can tell you for a fact that if your true main jet size is 137.5, then there is simply no way that an increase to 142.5 or anything close to that is enough for K&N pods. If you believe the Mac pipe only flows equally to the stock pipe, that's fine and if true that makes it simpler in theory. That's why I question your throttle position tests or the bike being ready to re-jet. I have never jetted a bike for pods with good results without going up at least 3 full sizes on the main. Pods, even cheap pods if in good condition, effect air intake that much, even if the exhaust isn't a good flow "match" for them. If the pipe is quality and flows well, more than 3 full sizes will allow the pods to flow their best.
If you're holding the throttle open fully for about a mile and chop off and get rich reads with an increase of 1 full size, something's wrong elsewhere. Something's been missed. Poor compression, weak/poor spark, incorrect plugs, retarded timing advance, float levels, etc, or any combo of things.

 

[t3rmin]

Hmmm. Not sure if you're testing each circuit at the appropriate throttle position. That will cause frustration if you do.

As we're dealing with vacuum slides, I don't think in terms of hard throttle positions, since for any given throttle position the position of the slides is dependent on load/vacuum. So whacking the throttle open from a slow speed or in a high gear could yield a very different mixture curve than a roll-on to WOT. This is particularly important considering the following:

Right now I've got it at the stock jets (137.5) and needles in forth position (clips 1 notch down, needles up/richer). Off the line power is *much* improved. But I get two very different behaviors between an (aggressive) roll-on to WOT and whacking it wide open.

Roll-on: Smooth power from idle to redline. Feels great. Pulls about like an 1100 should.

Whacking to WOT: Great power down low, but when it gets to around 5k RPM it burbles and stumbles until about 7k, then kicks in again and pulls hard to redline (8.5k).

What really surprised me is the plugs. They're greyish/tan. Last iteration (137.5, needle clips in MIDDLE), they were definitely white. Didn't have the desire to do real plug chops since it's 28 degrees outside, so this reading and previous were immediately after parking.

I hope the bike was otherwise tuned and ready for the re-jet.

It's in a good state of tune otherwise.

 

[KEITH KRAUSE]

Well, I used to type out small novels trying to explain things but it sounds like you wouldn't really listen anyway. I just don't have time for that anymore. And don't take these words as me being angry or something because that's not so. I do remember helping you in the past...a lot. I just try to add my thoughts and the reader can use it or not.
My thoughts on the importance of throttle position and its relation to vacuum differ than yours. That's fine. I have my way of testing and that's all I can offer. VM, CV, too similar to argue about.
In the real world, you shouldn't try to gag or "confuse" the carbs by "whacking" them open. Under what conditions would you do this? A typical roll on gave you good results. But whacking it open revealed a stumble because you forced the carbs to operate in a way they're not designed to.
Whacking it open means you want to accelerate hard. You wouldn't whack it open from a dead start, you'd be revving it first as you prepare to launch. And if you wanted to accelerate hard from a cruising point you would either roll it on aggressively as you put it, or shift down and roll on, or you'd be in the powerband already and then it almost certainly would respond as you want, even if whacked open.
Maybe I'm wrong about how you're throttling this bike but you can't just whack open any bike from very low rpm's and expect perfection.

 

[t3rmin]

Well, I used to type out small novels trying to explain things but it sounds like you wouldn't really listen anyway. I just don't have time for that anymore. And don't take these words as me being angry or something because that's not so. I do remember helping you in the past...a lot. I just try to add my thoughts and the reader can use it or not.
My thoughts on the importance of throttle position and its relation to vacuum differ than yours. That's fine. I have my way of testing and that's all I can offer. VM, CV, too similar to argue about.
In the real world, you shouldn't try to gag or "confuse" the carbs by "whacking" them open. Under what conditions would you do this? A typical roll on gave you good results. But whacking it open revealed a stumble because you forced the carbs to operate in a way they're not designed to.
Whacking it open means you want to accelerate hard. You wouldn't whack it open from a dead start, you'd be revving it first as you prepare to launch. And if you wanted to accelerate hard from a cruising point you would either roll it on aggressively as you put it, or shift down and roll on, or you'd be in the powerband already and then it almost certainly would respond as you want, even if whacked open.
Maybe I'm wrong about how you're throttling this bike but you can't just whack open any bike from very low rpm's and expect perfection.

Well you're probably right about that. Especially with drilled slides that might be raising faster than I'm used to, I probably need to modulate the throttle more carefully.

So here's the latest: I experimented with float levels a bit. Stock spec is 25.7mm. I had 'em at about 25mm (per information from the XS forums) all along. I went up to 26mm and tried the 142.5 and 145 mains again. Way more blubbery in the middle and didn't pull as hard on the top end. 145 worse than 142.5. Did a plug chop in the soggy middle area and result was... inconclusive. Center electrode was fairly clean and grey, but plenty of soot around the edge.

Went down to 24mm and dropped 137.5 in again. Runs a little worse in the middle (agressive roll-on, 5k RPMs) than it did at 25mm with 137.5's, but it's maybe a little better off the line. Down low and up high this jet definitely pulls harder than 142.5 or 145. All signs still pointing to *rich* in the middle. Note it's easy to pull "past" the slobbery area and then it's a rocket with 137.5's, with the 145's and 142.5's you can't hardly get past it (especially in a high gear).

(Obviously float levels shouldn't have much of an impact at the throttle openings/RPMs I'm having the most trouble with, but I wanted more confirmation that what I'm fighting is a rich condition. And I was frustrated and had lots of time on my hands today.)

Also I'm wondering if perhaps the stock XS airbox flows more compared to a GS airbox, and there's not a great deal of difference between that and pods, since I'm also surprised that the stock jet runs the best. I do still have somewhat restrictive stock-style exhaust, too.

To recap:
The good: Pilot, float level (ballpark), beginning of needle circuit, mains
The bad: middle/end of needle circuit

How can I lean out the middle/end of the needle? If I lower the needle, it's sluggish off the line (begining of needle). Have to change the taper? That seems like it should be more of a fine-tuning thing...

 

[t3rmin]

Or another thought: maybe I should try using shims for 1/2 steps, as you mentioned. Maybe try 3.5 and 4.5?

 

[KEITH KRAUSE]

Since you've tried both position 3 and 4 from the top with (if I remember) lean and then rich symptoms respectively, then the most logical thought would be to use a jetting spacer (typically .022" thick) to achieve position "3 1/2". Place the e-clip at position 4 from the top with the jetting spacer directly on top the clip. Maybe that will fix things.
If that doesn't work then the air jet could factor in here. I believe those carbs have a pilot air jet and a primary air jet. Pods many times require air jet changes too.
Another thought would be to change the jet needle size or the needle jet size. You're getting in a bit deeper there. Needle jet change isn't normally needed with your mods. Jet needles often need changing. Heck, you could even have worn needle(s) or needle jets causing a problem.
I'd try position 3 1/2 first.

 

[KEITH KRAUSE]

Or another thought: maybe I should try using shims for 1/2 steps, as you mentioned. Maybe try 3.5 and 4.5?

Yes. I took awhile sending my previous reply about a 1/2 position change and didn't see your latest reply until I sent it.