Riders Of Vision

A recent posting by Night Vision really struck a responsive chord in me. He said: "I'm running 127.5 / 130 mains and some #64 fuel pilots I made... got rid of a pesky 4.5-5k rpm surge that was driving me coconuts..".  He also commented that a good thing about V carbs was that they allowed for jet changes to tune out carb drivability problems.

Of course, I'm no doubt running late with this brain storm, but instead of cursing V carbs and all their idiosyncrasies we should recognize the core problem and fix it.  I'm thinking that V carbs were factory tuned to comply with then current and future anticipated EPA emission standards.  The fix would be what Night Vision has stated.

Over the years almost every bike mag test I've read where the bike was carburetted, the mags complained about drivability problems and recommended jet kits as the fix.  In the cases where they have installed such kits themselves to cure the problems, the bikes aways ran much better and up to their full potential.

The V stumble and mid range roll on hesitation are issues that have plagued my '83 throughout its' life.  Even when it was running great, which was most of the time, these issues remained.  Night Vision is on the right track.  Speak up, ya'll.

if we could track down Blake, he'd be the one to get to do some testing for us, he has (had?) a VFR meter...  an exhaust gass anyalizer would be needed too.

and you know what, after all the technology was applied, the most importaint final tuning aid will be seat of the pants   ;D ;D ;D

Could be something in that...

Euro Fiche lists air jet sizes for the Euro (11U) as 120.0, versus 130.0 for the US82 (11J).  Both have the same BD34 carb / passive flapper setup.

My carbs were changed to 130 main jets in both carbs sometime in the mid to late 80's -I have no vacuum flapper air box (still pissed at the dealer I bought the V from in 1984-he should have installed the kit!) As some of you may know I put restrictive plates on my carbs for many, many years, took them off last year and only noticed a weeeee bit of difference-and have since left them off-I could probably pull up a hill (rolling the throttle) starting at 3 grand in fifth just a weeee bit better with the plates on as opposed to them off-I may want 4th gear now-but the difference is soooo slight. I have never taken the caps of my carbs and frankly after all these years I'll bet I would find the the screws frozen up.

I did have the Vision lag before, what is nuisance that was-especially in stop and go traffic. Will what I have done work for you-who knows??? I seem to have the passages clean and the carbs adjusted or am I just fortuneate???

I think you have an interesting point QBS.   

You are probably right on...  most 80's bikes were set up pretty lean and did/do respond well to slight re-jetting, shimming the needle, etc...

Keep in mind that adding ethanol (hate to bring this up again) also effectively makes the bike leaner if no other changes made.... takes more fuel to make the same air-fuel ratio.

Very clean carb is the place to start.  The carbs are very much like Weber carbs and I can tell you from much experience that a slight increase in idle jet size can make a big difference in situations like this.  The idle jet supplies fuel not just at idle but also in "transition"...  That's what all the tiny holes in the side of the barrel just above the throttle plate are about.  Idle jet has some influence well past idle throttle opening and rpm.

Steve

Quote from: fiat-doctor on August 10, 2010, 01:59:18 PM
You are probably right on...  most 80's bikes were set up pretty lean and did/do respond well to slight re-jetting, shimming the needle, etc...

Keep in mind that adding ethanol  (hate to bring this up again) also effectively makes the bike leaner  if no other changes made.... takes more fuel to make the same air-fuel ratio.

Very clean carb is the place to start.  The carbs are very much like Weber carbs and I can tell you from much experience that a slight increase in idle jet size can make a big difference in situations like this.  The idle jet supplies fuel not just at idle but also in "transition"...  That's what all the tiny holes in the side of the barrel just above the throttle plate are about.  Idle jet has some influence well past idle throttle opening and rpm.

Steve

agreed... I should also mention that some of us have been running Startron fuel treatment along with premium gas. I have been taking her out on these hot and humid 90 degree evenings and she is still running great....

I'd say the larger jets, and a couple more pennies a tank for the Startron and premium have made a big difference


oh yeah, look for Startron at a marine place... they have the more concentrated flavor 8 oz treats 128 gallons... I went to West Marine

Quotelists air jet sizes for the Euro (11U) as 120.0, versus 130.0 for the US82 (11J

The air box mod kit comes with (according to what I've read) a 135 pilot air jet for the rear and a new float chamber cover for the front with a jet installled but doesn't give the size. My 82 has the updated airbox and a 135 air jet in the rear but only a 120 in the front.  Is this normal or should I be looking to change that?

As far as I can tell Air Jets are always identical Front/Rear.
I'm currently running 135 in both with vacuum flapper, as are a lot of other people here.
However I have a pair if 120s on order

If you change the jets, you will need to re-do your mixtures and sync

I'm trying to approach re jetting our V carbs for superior drivability in an organized manner.  So, lets begin by identifying all the jets in a V carb.  For the sake of a lack of initial confusion, we'll consider the jetting systems for '82, '83, and front and rear carbs all to be the same.  Therefore, the following list is for a single carb.

If I miss something, make an erroneous statement, or call something by an inaccurate name please speak up.

Items:
(1) Air Jet mounted in carb top, Main Air Jet?

(2) Main Fuel Jet aka main Jet, accessed through the float bowl.

(3) Pilot Jet, aka Low Speed Jet, aka Idle Jet.  Mounted deep in the carb body.  Accessed from the bottom of the carb after the float bowl is removed.

(4) Emulsion tube jet.  Mounted in the carb body.  Easily, accessed from the bottom of the carb after the float bowl is removed.


Questions:

What does item #4 do?

What does item #1 do?  I realize that its' sizes are different for front and rear carbs.  Why?

I'm not absolutely sure, but I think item #2, the Main Fuel Jet, is a #50 and is the same for both '82 and '83.  I also suspect that #50 is a good size for max. power from our engines.  Anyone think otherwise?  Cheers for now.

QuoteAs far as I can tell Air Jets are always identical Front/Rear

Interesting. I have (2) '82's that have 120 in the front and a 135 in the rear.  Just curious, why the 120's on order? Experimenting or do have a theory you're working on?

QuoteI'm trying to approach re jetting our V carbs for superior drivability in an organized manner

A noble if not monumental task! I get the feeling the Yamaha engineers couldn't agree and you're asking a group of forum members to?

I don't have an '83 but I understand it's carbs to be significantly different than the '82? I've also heard the '82 has an early and later type carb? Treating them the same may make for a tidy discussion but could prove problematic regarding flow properties, performance, etc. I personally don't know how different they are, just thinking out loud.

Quote1) Air Jet mounted in carb top, Main Air Jet? What does item #1 do?

Speaking of disagreement, my manual and the parts fiche identify this simply as Main Jet. Unless I'm not reading it correctly, the instruction sheet for the air box mod calls it a Pilot Air Jet. As I recall, it meters air to the idle/slow speed circuit? I think I remember blowing air into it's mounting position and air exiting the fuel mixture screw hole  (maybe elsewhere too?) Maybe it also feeds the main jet tower through cross drilled holes? I haven't examined this yet so I don't know for sure.

QuoteWhat does item #4 do?

Mixes air and gas to form droplets that atomize better once in the venturi. I think. In slide throttle and CV carbs it's sometimes part of an assembly holding the needle jet at one end and the main jet at the other. I'm still new to these carbs but I'm guessing it's function is the same?

I'm not sure what you're talking about in your last item regarding #50 Main Jets?

The last paragraph in my above post mistakenly refered to item #1 when item #2 was the intended reference.  It has been edited to correct this error.

I'm still confused - 82's with vaccum air flapper have 122.5/127.5 main jets.

Item #2 is as described, the main fuel jet located in the float bowl.

QuoteI'm not absolutely sure, but I think item #2, the Main Fuel Jet, is a #50 and is the same for both '82 and '83.  I also suspect that #50 is a good size for max. power from our engines.  Anyone think otherwise?  Cheers for now.

I'm not questioning it's location but rather it's size. Your main jets are #50?Really?

Guys, remember these are old carbs. And likely most of us have leaking throttle shaft seals. This alone makes the bike lean at lower rpms. But as the rpms get high enough the seals will tend to do their jobs. Meaning , don't go crazy with the BIGGER gas jets or smaller air jets.I had an '82 that was too rich and did not drive proper till the flapper was set partially open. And Joevacc had the same issue on his. SO 135  pilot airs in my case was good for my '82 and I probably could have used 140's. What I am saying is. Not every bike is the same.  I found a set of carbs for my '83 where the leaks from these seals was minimal. And the stock jetting works great on MY '83 NOW. Previously it was terrible. How many of you have seen 11,000 on the tach in 4th gear? I have many times. For you kids and squids out there, with my euro gears, that's about 106 on my spot on digital speedo . This proved to me I was not rich on top.... And since I have NO STUMBLE at 4000 in any gear,  all else is just fine.  Yes, she runs quite well, thank you ;D and close to 45 - 50mpg most of the time.

Quote from: Rikugun on August 11, 2010, 10:53:07 PM

QuoteAs far as I can tell Air Jets are always identical Front/Rear

Interesting. I have (2) '82's that have 120 in the front and a 135 in the rear.  Just curious, why the 120's on order? Experimenting or do have a theory you're working on?

Take a look at parts fiches, stock air jets are definately the same for all models.  The RJ flapper kit came with a new 135 for the rear, and a new top for the front carb with a new (unspecified size) jet installed.  Maybe it was a 120, maybe a 135, I cannot tell for sure, but I'm betting on a 135.

Basically by ordering 120.0 Air Jets front and rear I am switching to euro spec. I built my current bike to US (evil EPA) spec as that is all the data I had access to at the time.I only just found the 11U parts fiche a few weeks back, so am now enlightened.

My first XZ, now sadly demised was a stock Euro and never ever ever had a stumble - ever.  I don't know if it will make a difference, I don't have access to exhaust analysers, and can't afford a dyno day, but for $6 each, it's a pretty cheap to give it a go

I hope we get some dependable information from this thread that will stand the test of time. Hope also that our carb overhaulers (Cdnlouie and Rick G) will contribute their expertise so that this information becomes the definitive word on making Visions run like they are capable of doing. QBS, if and when this train of thought winds down, perhaps you could state what has been concluded in a post similar to your initial post. I really like this approach and if it is successful we can take the next step on a different subject. It might be that this manner of solving problems doesn't overwhelm any one individual due to the multitudes of problems and opinions.    BDC

okay then, there is a gas analyser in the workshop of course and last time I gave the bike a probe it came up lean at idle. Plugs are burning a good color though.

Sooooo give me some time, I will find where my jets are at, try some others etc, might even throw her on the dyno.

In my case there is something different in the setup as I have my extended air intake trumpets and freer air flow, I still have the flapper, need the flapper. There is no way I am going back to standard intake lengths, it just feels flat and unresponsive in comparison. I can feel there is more to be had from the change but simply haven't had the time to get to it.

Treedragon,
Could you please post a pic of your trumpet mods? I would be very interested in this.  Which model carb do you have? It's a Jap market XZ550D is that right?

Riki,
What can I say? I am as ignorant as anyone could possibly be, but every document I can find states matching air jets front and rear, even where there is some variation of the actual values. Yes, The Europe 11U is the same displacement, bore, stroke, cams as the RJ

Germany 11V      130/130              Parts Fiche / Service Manual    - 50PS Model Different Cams
Europe    11U     120/120              Parts Fiche / Service Manual   
US RK 83           140/140              Parts Fiche / Service Manual    - Different  BD36 Carb
                       130/130              UK Haynes
US RJ 82            130/130              Parts Fiche / US Haynes
                        120/120             UK Haynes
                        Unspecified/135   Air Box Mod Instructions
XZ400  14X        146/146              Service Manual                      - Diferent Capacity, Different Cams
                       145/145               Parts Fiche

roro, Thanks for taking the time to compile that info. It seems pretty convincing - same size front and rear. Now if we can just determine what is the best size! Of course, finding optimum sizes of the jets may only apply to some members. Some are running stock parameters and some (like treedragon) have modified their bikes - intake, exhaust, or both.

First off, #50 for main fuel is very wrong.  I pulled the main fuel from my '83s' front carb.  It reads 130.  I feel that, at least for my bike, that is a good size.  This data is not in line with data reported by roro for my bike.  However, with approx. 88k miles on it, it will still red line 5th gear.  This tells me that it's making good power, and in at least in the case of my bike, should be left alone.  Fundamental question: Does a bigger #jet equate to a bigger hole or visa versa?

I investigated the emulsion tube jets on a spare set of '83 carbs and found #180s in both units.

I feel that the jets that should be focused on are the primary, air, and emulsion tube in that order.  The emulsion tube jet may be ok as is, but I'm not sure.

What we need to determine is what is the functional relationship between the primary jet and the air jet.  If you mess with one, how does that effect the function of the other?

No doubt equally important, what is the effect of altering the size of the emulsion tube jet and or its' emulsion tube hole sizes and or number of them?  I vaguely remember, long ago and far away, a post from either an Aussie or Kiwi Vnary who had a lot interaction with Ducati aficionados.  He made a passing remark about altering the emulsion tubes on Ducati carbs for the better.  I think he said that he had done a similar mod to his V with positive results.  Hopefully he'll read this thread and speak up.  I really want to understand the Emulsion Tube Jet much better.  Until its' function is understood, no meaningful positive changes can be made.  My gut feeling is that the random midrange power loss that my bike and I suspect a lot of other Vs, experience at steady state cruise is related to this jet/tube.

Fiat-Doctor has made several comments regarding the similarities between our Mikuni carbs and Webers, and Weber related mods he has mad to our Mikunis'.  Webers are reported to be very tunable and, once well sorted, excellent and stable units.  The bike mag reviews back in the day made mention that V carbs were close copys of Webers'.

We need to determine what size our primary jets are.  This could be the starting point for V stumble elimination.

After reading the interaction between jasonm and Rikugun regarding leaky throttle shaft seals, it seems to me that such leaks would effect mixture a idle, but very little at larger throttle openings.  This is because so much additional air would be entering the carb, and thus lowering the vacuum, that the small shaft leak would go unnoticed by the carb.

Cheers guys.

roro

if it's any use the  Engine number is 25R,  Frame is 25R-004113
Which model carb I have no idea really, just one of the later ones I guess. Just sorting out which jet is actually what is bad enough before I have even started looking.

Pics are on the air box mod post. The idea of the extended stacks was to speed downdraft velocity.

the #50 jet is the fuel pilot jet on an 83
82's have #60 fuel pilot jets..

the 82 has different sized mains (122.5/127.5 stock) because of the difference in exhaust pipe length...
83's have different diameter headpipes than the 82s so they run the same size mains front and back..

you'll see different combinations on the air jets... but mostly I've seen 130/135 with the vac flapper here on the board.

rejetting is not as hard as some have made it out to be.... bottom line is each carb will be different... find out what works for you... there is no one size fits all...... but I still stick by my suggestion to go bigger if you're stumblin or surging.  

Smaller ID...thus the exhuast gases actually flow better at low rpm, if not all rpm.  So there was no screwing with different air jets.  And mains also allowed to be the same.  Simply...they got in correct in the 2nd year US models.

You may change jets until your blue in the face. Stumble is best eliminated by careful synchronization and adjusting  the flapper opening .

Quoteand adjusting  the flapper opening .

Rick, In what way - mechanical adjustments like bending linkage or flapper? Modify the vacuum control? Modifying the airbox opening? More details please.

the mounts for the flapper door are slotted so moving the door is a fine tuning sort of adjustment.  i think the screws are in plastic so don't strip 'em

Quote from: Rikugun on August 15, 2010, 02:24:44 PM

Could you clarify the 130/135 air jets you've seen on the board - is that just 82's? If so, much like with the mains, is that also due to exhaust length difference?

the parts fiche of the carbs on the yamaha site is for the 82 carb... the parts list shows 122.5/127.5 mains, #60 fuel pilots, and 130 air jets..

if you look at the flapper update instructions, http://www.ridersofvision.net/Technical/Airbox/airbox.html

they list a 135 air pilot for the rear.. they also list a 122.5 main for the front carb in the flapper kit...which contradicts the parts fiche? why intall a 122.5 front main if it was stock?


you'll find other discrepancies in the haynes manual too... hope that clears things up  ;D

i think the differences come with different printing dates...  some of you may not know this, but the Yamaha workshop manual valve shim chart is wrong too...

Quote from: Night Vision on August 17, 2010, 09:35:17 PM

Quote from: Rikugun on August 15, 2010, 02:24:44 PM

Could you clarify the 130/135 air jets you've seen on the board - is that just 82's? If so, much like with the mains, is that also due to exhaust length difference?

the parts fiche of the carbs on the yamaha site is for the 82 carb... the parts list shows 122.5/127.5 mains, #60 fuel pilots, and 130 air jets..

if you look at the flapper update instructions, http://www.ridersofvision.net/Technical/Airbox/airbox.html

they list a 135 air pilot for the rear.. they also list a 122.5 main for the front carb in the flapper kit...which contradicts the parts fiche? why intall a 122.5 front main if it was stock?


you'll find other discrepancies in the haynes manual too... hope that clears things up  ;D

You are right NV , but do you know that all XZ's were shipped with a front 122.5 as per the parts fiche.  Fiches are revised often, expecially in the early period.

In the flapper modification instructions pg3 it states...

[note] For the front, pilot air jet is provided on the float chamber cover assembly.

That does not suggest a 130 Front to me.

Quote from: roro on August 18, 2010, 02:12:13 AM

In the flapper modification instructions pg3 it states...

[note] For the front, pilot air jet is provided on the float chamber cover assembly.

That does not suggest a 130 Front to me.

good catch? but I'm not sure  :-\

before I started molesting my Vision... she had plugged pilot screws, the flapper mod with the updated front carb top, and 130/135 air pilots.... I assumed this was the correct configuration and that a dealer must have installed the update because the previous owner was a poet... not a tinkerer... kicker is; I had a new front top in a box from a kit and scavenged the jet without paying attention to the size  :-[ ... at the time, I was just gathering jets from here and there for jetting games

Quote from: Rick G on August 17, 2010, 04:12:42 AM
You may change jets until your blue in the face. Stumble is best eliminated by careful synchronization and adjusting  the flapper opening .

Rick, I tried that... a few times, never worked for me.  Jason has his set so it is opened slightly while at low draw...

I think the stumble is caused by a sudden lean situation where the flapper opens too quickly.. my reasoning being is the two nickles trick that slows the opening on the non-vacc doors... that smoothed out lots a stumbles on non updated 82s

dirty/plugged jets will cause an extreme stumble... again a lean situation

Just a few of my thoughts.
I don't have my notes from racing a stock vision anymore. However I remember running stock jet sizes when I had a stock exhaust.  I would agree with Rick. You can mess around all you want with jets and not solve the stumble. I found a solution to stumble both on my racer and stock street bike. It was to retain all stock jets and adjust the Accelerator pump shaft. You can screw it in and out and that will give you more or less of a shot of fuel when you crack the throttle as well as affecting when the squirt happens I think.
I had access to a dyno during the time and we screwed with everything. Only to return to the original jets, Flapper and YICS. If you have any leaks in the YICS, or the hoses are pinching flat from suction.  You are spinning your wheels trying to get rid of stumbles. Also make sure your intake boots aren't cracked and everything is tight. You'll get nowhere fast if you have intake leaks.

Remember gas is crap now too, That doesn't help. I would stick with 92 octane.
Good luck.

The flapper air box instructions tell you to lengthen the accel pump rod by 5 mm over the stock length. It would be nice to no what the stock length is to establish a baseline.

I gotta tell ya, I'm not sold on the YICS. I removed it to see if possible leaks were contributing to my running woes. The surge, stumbles, and fading idle at lights are present with and without the YICS installed. I don't have access to a dyno to compare peak power, but it doesn't seem to make any difference in driveability.

Quote from: Rikugun on August 19, 2010, 11:56:22 PM
I gotta tell ya, I'm not sold on the YICS... but it doesn't seem to make any difference in driveability.

;D :D :D :D :D :D :D :D...welcome to the club, LOL.

           

I'm not sold on the YICS either.
I should have stated that better.
If your YICS is still on the bike make sure you have no leaks in the plumbing. If its gone be sure to plug the holes in the heads.
I do not have it on my racer. I remember on my street bike if those hoses had cracks then it ran poorly and off idle was not smooth.
As soon as I replaced those hoses it would run better. I never took off the system on my street bike.

Who cares where the stock setting should be on the pump rod. Take a measurement of the threads showing. Then go for a ride. Be very sure your all the way up to normal temp. Then adjust the rod half of turn or so. ride awhile and see if it changes. Stop and adjust another half of turn. I would continue in the same direction till it either runs better or you get to the end of the rod. If it still isn't right adjust it back to the measurement you took and then start the process in the other direction. I would ride 5 miles or so at least between adjustments.
Remember this is with CLEAN carbs. If all the passageways in your carbs aren't clean your wasting your effort.

Quote from: johnclemens on August 19, 2010, 09:18:28 PM

I would agree with Rick. You can mess around all you want with jets and not solve the stumble.

the thread topic was drivablity

I'm was not suggesting jetting to cure "plant yo face on the tank / clear n syc yur carb"' stumbles.. more of a tweaking your mixture to rid of surging... maybe hestitation would have been a better verb 

I'll add my 2 cents worth.  I worked at a Yamaha dealer in the mid 80's when we sold 82 Visions brand new in 84' & 85'  I was the Vision setup guy because no one else there could get them right.  I have some notes from the Yamaha Tech rep back then that I will try to scan and post. We always replaced the following parts when we took new bikes out of the crate:

Fuel Tank if any rust was present
Install the Vacuum Flapper kit
Clean Carbs

Then I would set them up with the following specs.

Once warmed up at idle (1300 RPM) CO (Carbon Monoxide) was set to 2% using the idle air screws and an exhaust gas analyzer.  This was critical to get rid of the stumble.  Unfortunately most of us don't have an EGA in our garage which makes this impossible to set.  If it is ever set correctly at 2% don't ever touch the idle air screws again because if the mixture is off at idle something else is wrong.  This setting is a big deal in getting rid of the stumbles.  Yamaha stated this at the time.

Verify the accelerator pump nozzle is spraying BETWEEN the throttle plate and the bore wall.  If it is not, carefully bend the nozzle and recheck until it sprays correctly.   If fuel spray hits the plate or wall stumbles will result and all the other adjustments are a waste of time.  Every new bike I saw this was never right from the factory.  I adjusted everyone.

Set the Accelerator pump adjustment rod length to a minimum of 50MM (Range 50-60MM recommended)  Measure the distance from the centerline of bend in the rod to the adjuster on the opposite end of the accel pump rod.  This adjustment can loosen over time so use blue loctite or clear nail polish to hold the adjuster in place.  My bike got stumbly a few years ago I found the adjustment had changed to 45MM.  Resetting this to 50MM made the problem go away.  I tried to always set this to the 50MM setting as other settings either cause stumbles or will reduce fuel mileage. 

Synch Carbs after the above adjustments this is important.

Verify 18-20 CM of mercury vacuum are present.  18-20CM of mercury are required for the vacuum operated airbox flapper to work properly.  If everything above is correct this vacuum setting should be correct.  The other cause of low vacuum could be low compression but we were dealing with new bikes so this was not an issue.

Verify there are no leaks in the YICS box.

Verify the Emulsion tubes are spotless clean

All other Jets were stock as we were selling new bikes that had to confirm to emissions.  Stock jets with the stock air box and exhaust system will WORK CORRECTLY if all the setup is right. 

I've owned my Vision since 1984 and it is as right today as it was in 1984. Premium gas is good idea.

dpequip,Do I understand that the Vision stumble can be eliminated (assuming everything is clean and functioning properly) by adjusting the accelerator pump adjustment rod length until the stumble goes away? Will the carbs need re-synching after each accelerator pump adjustment?    BDC

dpequip, your posting is a welcome piece of information, especially for low mileage bikes that haven't had their fuel systems ravaged by the hand of man and miles of road.  It needs to locked on the board as a must read. Thank you for following this thread and making this contribution.

Can you make a case for jetting V carbs richer or leaner in some way to enhance drivability?

I read your other post first (with the pdf) and commented there but let me say again thanks for the great info. Always good to have the perspective of an "insider"!

Very good info, especially the accelerator pump rod length. Somebody on another post suggested making the adjustment in 1/2 turn increments. The 10mm range of adjustment makes that a little tedious. One of the 'stumble cures' I used on my '83 was a 3-4 turn adjustment(longer than stock) and carb synch.

Quote from: Re-Vision on August 21, 2010, 02:40:57 PM
dpequip,Do I understand that the Vision stumble can be eliminated (assuming everything is clean and functioning properly) by adjusting the accelerator pump adjustment rod length until the stumble goes away? Will the carbs need re-synching after each accelerator pump adjustment?    BDC

boy, that would be nice huh? lenghtening the pump rod is part of getting rid of the stumbles and is part of the flapper mod directions post in the tech section....


hmmm I wonder what lenghtening the pump rod does ??????

oh!, maybe it gives her some more gas?   ::) like I've been saying.. . feed me

I would think that lengthening the rod would cause earlier fuel injection into the carb throat when going to full throttle, the adjustment would be to provide fuel at the exact time needed to prevent stumble from too much or too little gas when accelerating. Just from observing the fuel being pumped into the carb, I would guess that the amount of full sprayed is nearly the same each time.     BDC

In the airbox manual, it states that lengthening the rod is for USA and Canada models only.
Perhaps the Euro Australasian models already set longer. I guess we will never know.