Buddy 125 upgrade to Prima 161 Big Bore Kit

Rusty Shackleford · Post by **Rusty Shackleford** » Fri Sep 21, 2012 12:00 am

jaswol wrote:I did the 161 kit with a Prima pipe and NCY big valve head. The scooter runs great. Lots more power and top end speed. I am reaching 75mph indicated on my speedometer.

I am looking to upgrade to a 26mm carb and upgrade the transmission now! I am afraid I am hooked...

I'm a little embarrassed to be asking, but what will the NCY big valve head do? I see it recommended along with the Big Bore Kit itself, but have heard mixed reviews. Some say "yeah, go ahead and do it when you do the kit", and others seem to be of the mind set "the big valve head isn't really worth the extra money". I'd definitely like some feedback here. I've been eyeing the same mods for the 125.

thatvwbusguy · Post by **thatvwbusguy** » Fri Sep 21, 2012 12:29 am

Bigger valves allow more intake air (and exhaust, since they need to be balanced). This in turn allows the big bore kit to breathe better and make more power when matched with proper carb jetting.

Rusty Shackleford · Post by **Rusty Shackleford** » Fri Sep 21, 2012 3:24 am

Cool, that's about what I thought. So the new cylinder head will increase the volume of intake and exhaust to accommodate the larger displacement. The question I had for the shop was whether a performance exhaust was needed to move the resulting increased flow. The mechanic said no, I could just keep the stock pipe if I wanted it to stay quiet.

Do any of you guys run the big bore kit and head with the stock exhaust?

Rusty Shackleford · Post by **Rusty Shackleford** » Fri Sep 21, 2012 8:39 pm

...also, is the stock carburetor able to provide adequate fuel via up-jetting, or is there any merit to upgrading to a larger carb? My Buddy is currently stock, and the plan, in my mind, is to get the 161cc cylinder kit, the big valve header, and re-jet the carburetor (keeping the stock exhaust). Is this a feasible setup?

Also, why would you change the roller weights, let alone the contra spring because of the kit? Does the big bore/header shift the power band up into higher RPM's? I haven't seen any dyno evidence supporting that. In fact, the Scooter Works website has a dyno chart showing that the big bore increases power on the bottom end, the header increases power on the top end, and the resulting curve is largely unchanged. There's a slight bias in the curve after modification towards the low end, but the disadvantage of reaching higher gear ratios too early via weights/spring sounds like it would make the bike accelerate slower to me. Is this wrong? After researching the topic of roller weights and contra springs, it sounds like their job is to control upshift and downshift RPM's, respectively. Unless there's a serious change to the curve, I'd think it'd best to leave them stock. Genuine wouldn't have put too light of weights in out of the factory and needlessly decreased fuel economy and power, nor would they have put in too heavy of weights stopping needlessly shy of the torque curve for the same reason. That's supposed to be the benefit of a CVT and would defeat the purpose. Check this out...

Am I missing something?

thatvwbusguy · Post by **thatvwbusguy** » Fri Sep 21, 2012 9:08 pm

You are adding about 30% additional displacement, which is a pretty sizable jump. Without question, a new carb, an exhaust that flows better and new rollers will allow you to get the most performance out of the big bore kit.

With that said, you can almost certainly get it to run acceptably with the stock carb and exhaust. It is more a question of how much you want to tinker and tune to get the performance level where you want it.

Even though the engine on a small displacement scooter is a pretty simple beast, getting one tuned so you will have an even idle, proper operating temps and good power can be a challenge. If you can buy a kit consisting of a proven combination of parts, you will be way ahead of the game vs. trying to sort it out yourself.

Are you doing the work yourself, or is a shop doing it for you?

Rusty Shackleford · Post by **Rusty Shackleford** » Fri Sep 21, 2012 10:03 pm

I'm getting it done at the Genuine dealer. The mechanics were the ones that said if I just used the 161cc cylinder and big valve head, re-jetting the carburetor and keeping the stock exhaust would be fine. This seemed logical to me too since the stock (restricted) exhaust would compliment re-jetting the stock (restricted) carb. I'm aware if I had the Prima exhaust and bigger carb I could get a little more out it, but if we're talking a 35% increase in power VS a 45% increase in power; I'll take the hit, keep the exhaust quiet, and save on cost of the carburetor and additional labor if it'll still run smoothly without them (new carb/pipe).

Is there any particular problem with running the big bore/valve without a new carb/pipe? Will the stock carburetor not be able to be re-jetted to flow enough or something? I'd dare say most people who have the big bore kit don't have the bigger carb, and they also have the Prima exhaust (which I won't be using). I understand they may not have the big valve head, but I'd think they'd still need a higher flow of fuel to compensate for the increased air flow. As for the weights; what benefit would they give if the power curve hasn't changed? Thanks for your input in advance.

rick71454 · Post by **rick71454** » Fri Sep 21, 2012 11:18 pm

Hello Rusty Shackleford:

You might do the Big Bore Kit 161cc stand alone to see what improvements you get before doing anything else.

That is what I did, and the torque is higher especially from the start. The mechanic did a wheelee when he tested his work out. It goes 62MPH speedometer indicated comprared to 58MPH before the kit.

I will be tyring an assortment of roller weights soon to take advantage of the extra torque and move it to the top speed end. I expect it will go at least 5MPH faster.

Stay Tuned.......
Rick71454

thatvwbusguy · Post by **thatvwbusguy** » Sat Sep 22, 2012 8:44 am

Definitely go with what your dealer recommends over some stranger on a forum. They should stand behind their work if you follow their recommendations.

Once the engine work is all dialed in, you can play with CVT adjustments and such at your leisure (if at all).

Rusty Shackleford · Post by **Rusty Shackleford** » Sat Sep 22, 2012 4:36 pm

rick71454 wrote:I will be tyring an assortment of roller weights soon to take advantage of the extra torque and move it to the top speed end. I expect it will go at least 5MPH faster.

The reason I challenge the notion of changing roller weights for performance is because of dyno charts like this that show that the different weights simply control the RPM the engine maintains as the CVT controls the MPH speed. Heavier weights should only be needed if the engine is revving past it's optimal power range. Lighter weights are only needed if the engine isn't revving high enough to make the most power. The dyno below shows the lightest and heaviest weights at a disadvantage against the medium weights. On the top end, there's no added benefit, and in fact, the heavier weights only catch up to the power output of the lighter ones around top speed, but don't actually surpass them. The only way I could see a little heavier weight being of benefit is if the stock weights weren't heavy enough to reach the highest gear ratio before the bike couldn't overcome wind resistance, and it could do so with the big bore kit. Considering I can hit an indicated 65mph with throttle left of the bike stock, I don't think the stock weights are incapable of maxing out the gear ratio, but I'm new to CVT's and could be wrong. I'm just thinking that once you have the Buddy over an honest 60mph, it's not worth it to sacrifice power on the bottom end since the scooter isn't really made to maintain 70mph anyway.

This is all just my hypothesis. I would actually very much like for someone to refute it, because if there really is a practical benefit to heavier weights, I'll buy them when I do the kit.

BuddyLicious · Post by **BuddyLicious** » Sat Sep 22, 2012 5:11 pm

rick71454,

Did you by chance have the 2nd shop contact the first shop to inform them of their screw-up? I would fully expect for you to get at least a partial refund on the shotty work.This would really bother me if it happened to me.You deserve a refund dude!

Have fun with your new power.....

thatvwbusguy · Post by **thatvwbusguy** » Sun Sep 23, 2012 12:38 am

Buy some weights now and see what a difference a few grams can make with your stock scoot. The results will translate directly to the 161cc kit.

Regardless of what a dyno chart might indicate, in the real world changing roller weights has a very noticeable impact on the way a scooter operates. Everything I am stating here comes from personal experience tuning variator weights on several Yamaha Zuma 125's and a few various Honda's and Chinese Honda clones from 50-150cc.

I have spent quite a bit of time tuning CVTs to their rider's preference. I do this because I often find that a $200-$300.00 Big Bore Kit with everything else left stock will only provide about 1-2MPH more top end than simply tuning the variator properly. The BBK will always allow better acceleration from a stop, but without changing weights, you keep the same overall CVT gearing ratios and retain the same top speed.

In every case that I have seen, rollers from the factory are a safe balance between low end acceleration and top end speed. The drive belt often only travels 75-80% of the way up the variator face, which means that there is clearly a higher gear ratio available that will provide more top end speed.

OEM's are very good at knowing what will keep the customer happy vs. what will cost them money in warranty work. Because of this, they don't try to maximize performance on any of their stock product lines (this also gives them the opportunity to offer upgrades such as the 161 BBK through their preferred network of installers).

My wife's de-restricted Buddy 50 only gets the drive belt about 80% of the way to the top of her variator. She says that this is fine for her, but if I was going to ride it, I would want to optimize my top speed by a couple more MPH so I could safely ride in 40MPH zones without fear of getting run over. As she grows more confident with her riding abilities, I think she will probably come over to the dark side and start looking for a few simple mods.

People who drive in the city primarily tend to like quick acceleration, but don't have a chance to get up to top speed very often. For them, dropping the roller weights down a couple grams will give better response from a stop, but a little less overall top speed. The end result is less riders getting rear ended when leaving stop lights.

At the other end of the spectrum, I commute about 20 miles each way to work on my scooter (2012 Yamaha Zuma 125). Most of the speed limits are posted at 40-50 MPH along my route. This means that most of the cars around me are consistently travelling 50-60MPH. In stock form, my scooter topped out at 61MPH (indicated, 58GPS verified). With a couple changes of roller weights, I now consistently hold 65MPH (62GPS) on flats. This means that I am no longer at wide open throttle constantly and don't bounce off the rev limiter on a regular basis. I lost a minimal amount of low end acceleration with the roller swap, but gained a margin of safety for my riding conditions with an investment of about $35.00.

When my factory warranty runs out, I will most likely add a 155cc BBK to my scooter. This is a simple and well proven kit consisting of a piston, jug and a new fuel injector. There is no need to machine the case, replace the crank or upgrade exhaust. Until my warranty is up however, I will only make changes that are simple to change back to stock if necessary for warranty work.

Once I do the BBK, I will once again tune my variator for what I feel is the best balance of acceleration and top speed. If I leave my weights where they are now and add power and torque, I will be able to wheelie, but my top speed will stay the exact same. At this point I will also look into slightly taller gearing that will allow higher cruising speed at lower RPM's. This will also help to balance the MPG loss that is usually seen when adding engine displacement.

Rusty Shackleford · Post by **Rusty Shackleford** » Sun Sep 23, 2012 5:28 am

Interesting. Logically, I could see lighter roller weights providing slightly better acceleration. Also, if the stock weights aren't heavy enough to reach the highest ratio, I could see going up in weight providing slightly more top speed. I suppose so long as the weights weren't too heavy, the added displacement would compensate for the reduced RPM's, meaning the acceleration wouldn't be too much more, but you'd pick the gains up on the top by sacrificing them elsewhere.

This all definitely begs the question of what type of riding is typical for the individual. We live in an urban environment and only need to get the Buddy up to an actual 60mph on country highways, so I'll likely leave the stock weights to even out my gains, then try slightly heavier ones if the bike is running too close to full throttle at high speeds. There comes a balance point where you have to admit the bike is fairly tedious above an honest 60mph though, so the stock weights may end up being ideal. Thanks so much for your reply though. I was unaware that scooters aren't generally capable of reaching full high ratio. It's nice to know there's some wiggle room of that's the case.

Also, do you have any knowledge of the clutch/springs? I'd like the clutch to engage a little sooner. There's too much revving before the gears grab for my liking.

thatvwbusguy · Post by **thatvwbusguy** » Sun Sep 23, 2012 7:01 am

A stiffer contra spring coupled with softer clutch springs should engage quicker and stay in low gear (rear pulley closed) longer.

The stiff (higher RPM) contra spring is easy to find, but I am not sure that there are any clutch springs available that are softer than stock...

PeteH · Post by **PeteH** » Sun Sep 23, 2012 11:34 am

I don't know where that Dyno graph came from, but the curves are labeled for some teeny roller weights (3.5-6.5g). This does not resemble the weights you're discussing, unless I'm reading it completely wrong. Is this chart from a 49cc???

Rusty Shackleford · Post by **Rusty Shackleford** » Sun Sep 23, 2012 5:08 pm

Clutch Springs & Contra Springs...

thatvwbusguy wrote:A stiffer contra spring coupled with softer clutch springs should engage quicker and stay in low gear (rear pulley closed) longer.

CLUTCH SPRINGS: Softer clutch springs aren't a necessity I suppose. The buddy requires a little bit of throttle to start the bike, and my GF parks hers on her side-stand like I do with my motorcycle. I really don't want her accidentally driving off the stand and dropping it. Also, the stock clutch springs engage with a pretty good amount of acceleration upon a good twist of the throttle.

CONTRA SPRINGS: As for the contra springs, my understanding was not that they kept the bike in low gear longer (my understood role of roller weights, actually), but to drop the gear ratio when rolling off the throttle and when riding up hills. Importantly, I should back up and say that when I referred to the roller weights holding an "optimal RPM", I wasn't referring to the fastest possible acceleration, but more of optimizing the RPM for power without needlessly over-revving it, meaning not revving past peak power where the fuel economy would drop like a rock and engine wear would increase (not to mention an annoying loss in top speed). That said, my understanding is that the contra spring will force a lower gear ratio on hills, meaning the engine may in fact rev past peak power, but will still produce more rear wheel torque due to the mechanical advantage of the ratio dropping. This wouldn't be an ideal sustainable situation, but would provide the power needed to climb the hill. Also, the contra spring should also affect the bikes ability to "coast" when rolling off the throttle VS "engine braking". In my personal preference, a bike should be able to drop ratio on hills and be able to engine brake upon roll-off, leading me to want a stiffer contra spring for the Buddy. I understand why the stock one is the way it is. It's good for commuting; but a sportier riding style could benefit from a stiffer spring if my theory on their role is correct.

Could you verify my understanding of contra springs? Please forgive; I'm new to CVT's and trying to transpose all of this from my motorcycle knowledge.

Clarification on the Dyno Chart

PeteH wrote:I don't know where that Dyno graph came from, but the curves are labeled for some teeny roller weights (3.5-6.5g). This does not resemble the weights you're discussing, unless I'm reading it completely wrong. Is this chart from a 49cc???

Yes, I believe this chart is from a 49cc bike. The weights VS power curve should still be applicable though. There's 2 ways to increase speed; higher revs and higher gear ratios. The graph should apply to all CVT's. Lighter roller weights will accelerate from a stop relying more on revving the engine than increasing the ratio. This means that even if it revs past peak power, it should still accelerate faster because it's using a lower gear ratio (within reason). However, when approaching high speeds, there won't be enough weight in the rollers to reach the highest ratio, and the engine will likely be over revved already if not bouncing off the rev limiter.

To everyone:
I can see the logic of why some riders will use a little heavier weights after installing the big bore kit and header. It's an issue of the added power facilitating heavier roller weights, not necessitating them. I also didn't know the stock weights didn't reach full high ratio. That said, I understand the lower engine speed and less required throttle bumping the fuel economy back up and give a higher more comfortable top speed. How does a Buddy handle at 70mph, though? I'd imagine it would drift like crazy considering how small the tires are and how light the bike is.

Preliminarily, I'd like to have the engine rev to the torque peak off the line, ride the CVT up that flat portion of the dyno chart, then reach the top desired speed (around 65mph) at peak horsepower. This will indeed take some trials to achieve with much consultation from the mechanics. I'll be leaving the transmission alone and doing the big bore kit and header 1st to see what it does.

The Burning Question
It's becoming apparent that heavier roller weights and contra spring = faster up-shifts and down-shifts, repectively; and lighter roller weights and contra spring = slower up-shifts and down-shifts, respectively. The confusion I'm having is how to balance the 2 together. For example, does using a stiffer contra spring alone have the same effect as a heavier roller weight; ie: does the stiffer contra spring maintain a lower ratio the way lighter roller weights do? Is this not the case at all, and perhaps the contra spring does very little to maintain a low gear ratio, but functions solely to downshift? Either way, how exactly does the contra spring drop ratio on a hill? What physically happens to do that? The lowering of RPM's? If so, wouldn't the front pulley and weights drop to a lower RPM as well? I'm foggy on how the roller wieghts and contra spring affect each other. Can you guys please enlighten me?

thatvwbusguy · Post by **thatvwbusguy** » Mon Sep 24, 2012 12:01 am

In a nutshell:

The variator (drive pulley) works like this - The rollers travel outward from centrifugal force as engine RPM increases. Since the rollers are contained by the variator ramps on one side and the backing plate on the other side, this forces the inner pulley out toward the fixed outer pulley. This pushes the belt higher on the pulley faces, which results in higher gearing. Heavier weights come in sooner, so the variator closes quicker and shifts up quicker.

As the variator closes, the belt tightens around the rear driven pulley and begins to spin it. When it comes up to the RPM that the clutch springs engage at, the clutch expands and makes contact with the clutch bell and you start moving.

The contra spring is trying to keep the rear (driven) pulley together, so that the rear pulley stays in the lowest gear possible based on RPM. The stiffer the contra spring, the higher the RPM before the belt can force the rear pulley apart to allow the belt to drop down into a smaller (higher) final gear.

When you let off the throttle, everything goes back to it's original resting state. Very simple, yet incredibly ingenious at the same time.

JB

Rusty Shackleford · Post by **Rusty Shackleford** » Mon Sep 24, 2012 2:33 am

Roller Weights

thatvwbusguy wrote:...The variator (drive pulley) works like this - The rollers travel outward from centrifugal force as engine RPM increases...

That was my understanding, but if that's the case, it must not take much to force them out since the RPM's don't increase but so dramatically from 15mph-45mph. Makes sense I suppose. The roller weights are in "grams", so they're not very heavy to begin with.

Contra Spring

thatvwbusguy wrote:...The stiffer the contra spring, the higher the RPM before the belt can force the rear pulley apart to allow the belt to drop down into a smaller (higher) final gear. When you let off the throttle, everything goes back to it's original resting state...

If that's the case, then the contra spring would indeed have an affect on what RPM the engine is running at VS speed of the bike. I was under the impression that the roller weights determined up-shift rate, and the contra spring determined down-shift rate. So it is possible for a contra spring to impair the roller weights' ability to change gear ratio as quickly? If so, that sounds like it would slow acceleration and over-rev the bike. The drive belt is a finite length, so i wouldn't think the front pulley could expand if the rear one didn't contract, you know what I mean?

This is leading me to think the only way to run a stiffer contra spring to get faster down-shifting is to use heavier roller weights, which would defeat the purpose by killing the acceleration. I'm content with the top speed and rate of up-shift, but I'd like a little faster down-shift. Would a stiffer contra spring work with stock roller weights without limiting top speed? Thanks again for your help.

thatvwbusguy · Post by **thatvwbusguy** » Mon Sep 24, 2012 3:50 am

Running a stiffer contra spring does help somewhat with deceleration (engine braking) but you could never hope to achieve anywhere near the kind of engine braking that a chain driven bike has. Heavier rollers with the stiff spring would help, but at the expense of acceleration as you proposed.

At the end of the day, scooters are simply not meant to have great engine braking, it's just the nature of the beast. You can make small changes to influence performance feedback, but you are still at the mercy of friction and centrifugal force.

It should also be noted that really stiff (2000RPM+) contra springs tend to shorten average belt life. This is most likely because of the high pressures exerted across the relatively tight curvature of the belt at the rear pulley. High pressure and high heat are the nemesis of the CVT drive belt.

Rusty Shackleford · Post by **Rusty Shackleford** » Mon Sep 24, 2012 4:06 pm

What I'm gathering is that while the weights control the rate of upshift and the contra spring controls the rate of downshift, they have a certain amount of overlapping affect on each other. For example, a stiffer contra spring will make it more difficult to upshift, thus increasing the RPM's by whatever the spring is rated at. That being the case, would heavier weights simply counteract that effect? One has to exert more power than the other, otherwise the bike wouldn't shift. The roller weights have to be able to overpower the contra spring, so the question remains: Does a stiffer contra spring = same effect as lighter roller wieghts? I would think that it's more of a biased relationship, perhaps 80/20 for example. Contra spring = 80% control of downshifting & 20% control of upshifting. If a stiffer contra spring "performs" better, why would a scooter come with a lighter spring to start with? Why not just run the satiffest one possible that still allows full high gear?

On a related note: what physically happens that makes a stiffer contra spring help the scooter climb hills? I understand how it would drop the gear ratio back down when rolling off the throttle, but I don't understand how it would assist on hill climbing.

rick71454 · Post by **rick71454** » Mon Sep 24, 2012 7:00 pm

I replaced my stock 11g roller weights with three15g and three 14g from the Prima set of variable roller weights 6g to 17g. Cost is $45.
That may seem like a large jump in weight. But if it were too much, I would go lighter as a trial and error process.
I could also do this knowing that I had more torque from the Big Bore Kit 161cc.

At the top, end, I am getting around 64MPH indicated on level ground which is about an extra 4MPH compared to stock roller weights. I was also surprised that my uphill speed did not get worse, but actually a bit better and more consistant at 50MPH indicated.

If you change your roller weights yourself, dont forget to make sure the belt is in the larger diameter postion between each side of the pulley on the variator side and the smaller diameter poistion on the rear drive pulley side. This is so that you can reassemble the parts without stripping the threads at the end of the variator drive shaft.

Rick71454

thatvwbusguy · Post by **thatvwbusguy** » Mon Sep 24, 2012 7:44 pm

I think this will explain it more eloquently than I can and it has a cool animated gif. too!
http://www.teamcalamari.com/zuma/variator.html

Rusty Shackleford · Post by **Rusty Shackleford** » Mon Sep 24, 2012 8:01 pm

The stock roller weights are fine for now. It's looking like RPM's can be increased with either the weights or a stiffer contra spring. Lighter weights would be used if you're already okay with your rate of downshift and only want to increase RPM's. A stiffer contra spring would be used alone if you wanted to increase both your RPMs and downshift rate. Since a stiffer contra spring will increase RPM's, heavier weights can be used to lower the RPM's back down while still maintaining the increased downshift capability upon rolling off the throttle. Regardless of weights, a stiffer contra spring would presumably always increase belt tension since it's inherent in the role of the spring to begin with.

My understanding so far is...

lighter roller weights = higher RPM's with same downshift (limited by top speed loss)

heavier roller weights = lower RPM's with same downshift (limited by acceleration loss)

weaker contra spring = lower RPM's with decreased downshift (limited by insufficient belt tension)

stiffer contra spring = higher RPM's with increased downshift (limited by excessive belt tension)

heavier roller weights + stiffer contra spring = same RPM's with increased downshift (limited by excessive belt tension)

Sooooo, how does a contra spring help climb hills, again? Does anybody know? That would be another benefit of using the next contra spring up from stock and installing the big bore/header. Hills wouldn't stand a chance and the downshift + extra power would launch the bike out of corners. Sport Buddy!

rick71454 · Post by **rick71454** » Mon Sep 24, 2012 9:25 pm

Hello Buddylicious:

I did not have the second shop contact the first shop, because the second shop said that they did not want to get into the potential fray of it.

I did contact the first shop for at least a partial refund. They would not agree. In my final letter to them, I put into the context of a customer relations issue in addition to the shoddy work. They chose to lose me as a customer to save $250. It did really bother me.

Short of anymore intensive measures like BBB and or the Courts, I decided to just ride my scooter and refer to the first shop as less than postive in my experience. I do not recommend the first shop, but I do recommend the second shop to others.

I do agree with you I desrve a refund. I am having fun with the new power my Buddy has.

rick71454

thatvwbusguy · Post by **thatvwbusguy** » Mon Sep 24, 2012 9:47 pm

A stiffer spring grips the sides of the belt tighter. More friction = less slip.

Without heavy enough roller weights or sliders up front, the rear pulley won't be driven. The CVT is a balance. It has to be a balance or it doesn't function at all.

Buy a set of tuning rollers and a couple different springs and experiment when you get your BBK installed. I think that you will see that light weights and stiff springs are not the way to go. You will probably be able to do power wheelies, but your top speed will most likely be around 40MPH.

Also keep in mind that stiff contra springs have been known to eat belts quicker than a stock spring typically does.

Tuning is an important part of making your scooter perform exactly the way you want it to. It can take time to get everything right, but it is fairly easy to do and well worth the time and effort in the long run.

Rusty Shackleford · Post by **Rusty Shackleford** » Mon Sep 24, 2012 11:04 pm

I know what you're getting at and it's possible I may end up changing roller weights. You know what would help? Getting a tachometer for the bike. I'd like to have top speed at least at an honest 60mph. My only requirement in doing so is that it doesn't occur over peak horsepower. Ideally, I'd like to see peak horsepower at an honest 65mph. The engine kit should make that possible. Not sure what's up with the cylinder kit dyno above, but the typical data for a Buddy 125 is 9.5hp @ 7,600rpm. The question is if the variator is maxed out yet by that speed. Either way, I'll still tune it until 65mph = 7,600rpm.

JettaKnight · Post by **JettaKnight** » Tue Sep 25, 2012 2:44 pm

Rusty Shackleford wrote:
Also, do you have any knowledge of the clutch/springs? I'd like the clutch to engage a little sooner. There's too much revving before the gears grab for my liking.

Really? I'd much rather let the engine wind up a little first. Lighter springs will likely cause some movement and power transfer when idling. (i.e. the bike wants to pull away when sitting at a stop light)

I run with red springs - makes it easy to pop a wheelie when I want too but still lets me creep along at 8 BMPH or so.

JettaKnight · Post by **JettaKnight** » Tue Sep 25, 2012 2:58 pm

I'm running something like 12.5(?) g weights (sliders) and a mid range contra spring (red). For me, this is as good as it gets.

I can't quite work out the equation (dynamics always puzzled me), but you have two opposite forces: the spring which has a linear equation, and the opposite force from the weights which is non linear. These forces balance out to give you the ratio of engine speed to wheel speed. By increasing or decreasing the effect of the forces in relationship to the other you can change the final curve to be more linear or less linear therefore keeping the engine within a certain RPM range for a greater percent of the time.

Then there's the pesky fact that the rotational force doesn't always come from the engine, there's the force that results from drag, going uphill, etc. working on the wheel end of the machine...

Since I don't know the equations or really any of the variables or parameters, trail and error was the only way to get the right combination.

Like I said, dynamics isn't well understood by us electrical engineers.

Rusty Shackleford · Post by **Rusty Shackleford** » Tue Sep 25, 2012 4:13 pm

Now that I've learned what I've learned, I'll likely be installing this tachometer to see what the engine and transmission are doing. I need to know if the variator is maxing out before top speed. This will be obvious if the RPM's are no longer consistent and begin climbing in a linear fashion along with the speed of the bike. In that case I'll lighten the weights to near the lowest I can and still reach 65mph indicated, under the condition the engine hasn't passed peak power by then. In the event the variator isn't maxed out at 65mph and is still below peak horsepower, I'll lighten the weights until said speed reaches peak power. If it's somehow possible the variator isn't maxed out but the engine is over peak power, I'd raise the weights to bring it down.

The "peak power" concern is more for efficiency. For those who don't know, on a manual shift vehicle, shifting at redline yields better acceleration than shifting at peak power. The reason for that is that engine power is only part of the equation and most people fail to factor in gearing, which will multiply torque at the rear wheel higher in a lower gear that has passed peak power than a higher gear at peak power. However, cruising beyond peak power is not desirable as the peak is where the efficiency of the engine starts dropping like a rock. In fact, for economy, you'd be better off cruising at engine torque peak, which is near what I assume will be around where the CVT holds the engine RPM's until maxing out. If I can cruise around torque peak, max out the variator, then climb to peak horsepower at 65mph indicated, I'd consider that a perfectly optimized Buddy.

rick71454 · Post by **rick71454** » Tue Sep 25, 2012 4:41 pm

Hello Rusty Shackleford:

IN reference to your use of a tachometer, that is neat you know how to do that. I also did a visual with the transmission cover off my Buddy 125, when I was changing my roller weights. With all 6 six stock 11g roller weights: I saw the RPM go up before the variator even began to shift the drive belt into higher position.

Then I took the big jump to change 3 three of the 11g to 15g. I could then see the variator begining to shift the drive belt into higher position with lower RPM. Then I change the remaining 3 three 11g to 14g. Now I have 3 three 15g & 3 three 14g.

With my Big Bore Kit 161cc prevously installed, this improved my maxiumum speed and even improved my uphill climbs on moderately steep hills.

Rick71454

Rusty Shackleford · Post by **Rusty Shackleford** » Tue Sep 25, 2012 5:03 pm

There's always the ability trade top speed for power. The only difference with scooter is that the final drive ratio is fixed and the transmission gearing is able to be modified. On most vehicles, the transmission is what it is and the final drive is changed, cascading the effect. Once you realize this, you then realize once the variator is maxed out, it doesn't matter how heavy or light your weights are, the engine speed and final drive ratio are locked along side each other. There's no trade off of speed for power after that. The lighter weights only limit top speed if the variator isn't maxing out. When using lighter weights, it's not only the higher RPM's, but the lower gear ratio that provides the added acceleration. It's an exponential effect because now you have increased gearing coupled to increased rear wheel torque multiplication. This is why "a little dab will do ya" when it comes to gearing changes. The best way to see performance gains with gearing changes on a scooter is to determine what the top speed you're willing to cruise at is, then keep sacrificing top speed above that in favor of more rear wheel torque until you reach peak horsepower at that desired max cruising speed. In my case, it's 65mph indicated because country highways are 55mph, 60mph is only 5mph over and won't provoke a speeding ticket and allows for passing, and the bump to 65mph is to accommodate for the speedometer's optimism.

At that point, and to get back on topic, the only way to add performance is in the engine, be it a big bore kit, exhaust, etc. This is why I want the big bore kit and header. I posted the dyno from Scooter Works regarding those mods because a change in power curve would change what RPM I needed to target at top speed. The power curve looks about the same, so using a tachometer should get me close enough. I could find a shop that has experience doing dyno runs on scooters, but if the variator isn't maxing out I'd have to put in heavy enough weights to make sure it does by the time it hits peak power RPM. For now, I'm thinking I'll trust the "7,600" RPM figure floating around the web. The thing is, this is my GF's scooter primarily, and she follows me through the city, the suburbs, the country, everything but the interstate (where she rides 2-up with me). We have friends with motorcycles, too, and she's the only scooter. She needs to be able to hold her own on 55mph roads with us, per her requirement, not mine. The group is a mix of sportbikes, cruisers, and her on a Buddy 125. Hopefully dropping gearing, the big bore kit, the big valve header, and re-jetting the carburetor will make it a cake walk.