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I know the short answer is I need to get a tachometer to really know, but current performance has me wondering whether I am a candidate for a 20 tooth clutch.

Now on stock 21/68 gearing. GPS has me doing about 50 mph in 2nd gear, 60 mph in 3rd gear, and 70 mph in 4th gear. Online gearing calculators have me doing about 8,800 rpm in 3rd and 7,700 rpm in 4th, but I am suspicious of those numbers because the calculators also have me doing over 10,000 rpm in 2nd, which seems doubtful for a cast iron Malossi 177. On the other hand, Cd for these scooters must be dreadful, so who knows what I'm really turning at speeds where Cd is not such a factor?

Leaving the calculators aside, 50 mph in 2nd seems like a waste. The usual 22 tooth clutch mod would only make that worse. I wouldn't mind trading some top speed in 2nd if it meant more rpms and more top speed in 3rd and 4th.

Thoughts?
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Sounds good to me.

What gearbox ratios?

What size tyres?

Which calculator are you using?

Etc...
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Kowalski wrote:
I know the short answer is I need to get a tachometer to really know, but current performance has me wondering whether I am a candidate for a 20 tooth clutch.

Now on stock 21/68 gearing. GPS has me doing about 50 mph in 2nd gear, 60 mph in 3rd gear, and 70 mph in 4th gear. Online gearing calculators have me doing about 8,800 rpm in 3rd and 7,700 rpm in 4th, but I am suspicious of those numbers because the calculators also have me doing over 10,000 rpm in 2nd, which seems doubtful for a cast iron Malossi 177. On the other hand, Cd for these scooters must be dreadful, so who knows what I'm really turning at speeds where Cd is not such a factor?

Leaving the calculators aside, 50 mph in 2nd seems like a waste. The usual 22 tooth clutch mod would only make that worse. I wouldn't mind trading some top speed in 2nd if it meant more rpms and more top speed in 3rd and 4th.

Thoughts?
Jetting is too lean. This iron cylinder, if unmodified, would only achieve 10000 rpm if it were running lean. This is proven, as it won't do 10000rpm in 3rd (lean jetting lacks torque).
If jetted correctly, the max rpm in 2nd and 3rd are very similar. And the max rpm in 4th, for general road use, would be 500 rpm less.
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I guess the answer is can the set up pull the R's and make power in that RPM range?

the gearing calc's pencil out on paper, but I'd stack that against real world GPS and a tach before making a decision. at least with a clutch that's easily swappable, but the better answer is probably a primary swap (short 3rd and 4th) and gears for the specific range of operation.
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What gearbox ratios?
What size tyres?
Which calculator are you using?

Final gearing is said to be:

1st 15.38:1
2nd 10.46:1
3rd 7.24:1
4th 5.38:1

Tires are 3.5"x10".

There are several calculators:

https://www.scooterhelp.com/tuning/vespa.gear.calc.html
http://gearingcalc.free.fr/
https://www.lofstrom.net/vespa/

SIP also has formulas:

https://www.sip-scootershop.com/download/article/1/pdf/fa6fa8d4-75db-48e7-8d72-31c6952120a1/Gearbox+Technology.pdf?contentType=application-pdf

Results are all pretty close.

Jetting is too lean. This iron cylinder, if unmodified, would only achieve 10000 rpm if it were running lean. This is proven, as it won't do 10000rpm in 3rd (lean jetting lacks torque).
If jetted correctly, the max rpm in 2nd and 3rd are very similar. And the max rpm in 4th, for general road use, would be 500 rpm less.

If it is too lean it is only slightly and only because of seasonal temperature changes. Plug looks good to me.

Have one of those battery powered inductive tachs on the way.
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50mph in 2nd gear sounds really really high. I run the same kit on my Stella with the stock gearing, SIP Road, fancy reeds, etc, and 2nd gear runs out of power at 35-40 indicated, and the motor is screaming at that point. I get 70ish at the top end on flats.
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Kowalski wrote:
If it is too lean it is only slightly and only because of seasonal temperature changes. Plug looks good to me.
Plug looks good to me too. However, that type of colouring on the plug is not from running continuously at WOT for an extended period.
Very easy for jetting to go from rich mid throttle to to lean at wide open.
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yackee wrote:
50mph in 2nd gear sounds really really high. I run the same kit on my Stella with the stock gearing, SIP Road, fancy reeds, etc, and 2nd gear runs out of power at 35-40 indicated, and the motor is screaming at that point. I get 70ish at the top end on flats.
For me, 40 mph in 2nd is about where the splutter sets in when I'm too rich. It will go well beyond that once the splutter is dialed out. I have the Worb5 flowed crank, matched cases and a Malossi box, which could be part of what's going on here.

I am a smidge above 70 on the flats. If 20/68 gearing would let me pull 8,000 rpm in 4th, I would be faster.
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Doesn't look like I'll get my tacho for this weekend but, in the meantime, Jack's comments caused me to revisit jetting yesterday. As in the past, going up one point on the main jet causes the motor to fall flat at around 40 mph gps in 2nd gear (I would call it more of a bog rather than a splutter). That puts me around 8,700 rpm according to the gearing calculators, which is pretty close to the 8,800 rpm the gearing calculators are giving me in 3rd.

So, how do you know when revving out is good or bad? I thought these things didn't have redlines. If going down just one point on the main jet gets you another 1,500 rpm in 2nd, why wouldn't you do that? Should you just tune for WOT in 3rd and live with whatever that gives you in 2nd? In that case, I probably could go higher still on the main jet.

Doing 71 mph on the flats (gps said more but trying to err on the conservative side). That corresponds to about 7,900 rpm in 4th. Assuming the delta between 3rd and 4th is 900 rpm, do I gear up, gear down, or stay with what I've got?
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So to recap: sometimes revving out is good and sometimes revving out is bad. Reminds me of the routine about mastering the word "ass" in English.

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This is the 2 stroke jetting dilemma. One size main jet revs high with no torque, size up has max power. Bigger still has long term reliability. Next sizes larger go flat, then splutter.
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Jack221 wrote:
This is the 2 stroke jetting dilemma. One size main jet revs high with no torque, size up has max power. Bigger still has long term reliability. Next sizes larger go flat, then splutter.
Starting to appreciate the added nuance.

Only thing is I'm not seeing such a broad spectrum. For me it is a knife's edge. Main jet n goes flat at 40 mph. Main jet n - 1 revs to 50 mph. There is nothing in between. Anyway, I have no great need to do 50 mph in 2nd so left the "goes flat at 40" main jet in for now.

Itching to pull the trigger on one of those VMC 10 spring clutches, but which clutch cog to go with it? If the target drop from 3rd to 4th is 500 rpm and my drop with a 21 tooth clutch is 900 rpm, what would the NSM brain trust do?
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If you drop down from a 21 to a 20 tooth clutch, it's going to make your acceleration worst in 1st and 2nd gear, then hamper your 4th gear top cruising speed. The reason being is that the engine's powerband won't be able to match up correctly with your actual speed. It would be very inefficient acceleration since you won't be able to utilize the engines power. I don't know if that made sense to you or anyone else, or if i even explained that correctly. I did a bunch of experimenting with all sorts of clutch toofuses...20, 21, 22, 23, 24 in various P engines. If you want the absolute best transmission ratio for pretty much ANY sort of riding, touring, or racing (sidecars and offroad trail riding aside), then you would want a taller 1st and 2nd, keep 3rd about where it is, and a shorter 4th gear. Then match a taller clutch tooth count (depending upon cylinder) to complement it. My point is that i think a 20 tooth would make is suck. I'd install a 22t clutch instead. And if you don't want to ride as fast, then don't give it as much throttle. The same can be said about your current 21 tooth. If you don't want to ride fast, don't ride fast. But this is all from first hand experience and not from online calculators.
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Koso Proton tachometer was garbage. Shipped with dead battery. Replaced battery and just showed gibberish above about 5,500 rpm.
Can't recommend.
Can't recommend.
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New but related question: what clutch nut/washer goes best with a VMC 10 spring clutch?

I am seeing a so-called Cosa clutch nut, which looks like it is one-time use with no washer. Also seeing shouldered nuts with either wave or serrated washers. Seems like the shouldered nut/serrated washer combo is the current state of the art. Yes?

Also seeing references to spacer washers and shims for Cosa clutches. I "think" a spacer washer comes with the clutch. No idea what the shim is for.
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Kind of funny that Black Friday is a thing in IT and DE since they do not have Thanksgiving. Anyway, a 20% "Black Friday" discount from my preferred Italian vendor got me off the dime and I ordered the VMC 10 spring clutch and a 22 tooth gear cog. Winter is coming so it could be a while before they are installed and tested.
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Kowalski wrote:
Kind of funny that Black Friday is a thing in IT and DE since they do not have Thanksgiving. Anyway, a 20% "Black Friday" discount from my preferred Italian vendor got me off the dime and I ordered the VMC 10 spring clutch and a 22 tooth gear cog. Winter is coming so it could be a while before they are installed and tested.
Care to share who's giving 20%?
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norman wrote:
Care to share who's giving 20%?
RDV Scootershop. Think it ends today. Not sure if they know about cyber-Monday.

They are becoming my go to for Italian parts not readily available in the U.S. They are the only Italian vendor I've found that does not charge an arm and a leg for shipping. Which is not to say the shipping is cheap, but their prices are good so you still come out ahead.
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So I got my VMC 10 spring clutch and there is one thing confusing me. The instructions state "the aluminum disc must always be fitted last with the side without friction material outside." This suggests to me that one of the "corks" should only have friction material on one side. However, all 4 corks I received have friction material on both sides. What am I missing?

Edit: Never mind. The next paragraph says "N.B. In the '10 springs ergal' version the friction material is present on both sides of the aluminum discs. The last disc can be any of the 4. The sealing ring can be mounted onto the friction material without problems."
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VMC clutch with 22 tooth cog is in and clutching perfectly. Install was pretty painless. Only issue was the VMC has no place to hook the usual clutch holder tool. Ended up just zapping the clutch nut with my impact wrench. Was thinking I might have to clearance the clutch cover, but that was not the case.

Could not resist doing a short cold weather shakedown today. Results are encouraging, but I think more testing is in order. Set a new personal best of 75.4 mph (gps) on the freeway. Translates to roughly 8,000 rpm in 4th on the gearing calculators. However, that was on a bit of a downhill. Compared to the 21 tooth cog, not seeing much difference so far in top speeds in the various gears on the flats and uphills. As expected, revs are lower at normal secondary road cruising speeds (say, 40 in 3rd and 50 in 4th), which is nice and relaxing. Will need to wait for warmer weather to really put it through its paces.

As an aside, I was curious about the term "Ergal." Turns out that is a trade name for 7075 aluminum alloy.
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Kowalski wrote:
VMC clutch with 22 tooth cog is in and clutching perfectly. Install was pretty painless. Only issue was the VMC has no place to hook the usual clutch holder tool. Ended up just zapping the clutch nut with my impact wrench. Was thinking I might have to clearance the clutch cover, but that was not the case.

Could not resist doing a short cold weather shakedown today. Results are encouraging, but I think more testing is in order. Set a new personal best of 75.4 mph (gps) on the freeway. Translates to roughly 8,000 rpm in 4th on the gearing calculators. However, that was on a bit of a downhill. Compared to the 21 tooth cog, not seeing much difference so far in top speeds in the various gears on the flats and uphills. As expected, revs are lower at normal secondary road cruising speeds (say, 40 in 3rd and 50 in 4th), which is nice and relaxing. Will need to wait for warmer weather to really put it through its paces.

As an aside, I was curious about the term "Ergal." Turns out that is a trade name for 7075 aluminum alloy.
absolute best engineered Cosa style clutch in the market; no doubt.
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GickSpeed wrote:
absolute best engineered Cosa style clutch in the market; no doubt.
but if it were the best engineered, wouldn't it have a way to hold it while you torque it?
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sdjohn wrote:
but if it were the best engineered, wouldn't it have a way to hold it while you torque it?
I use a rope to stop all my pistons; just like any other clutch I install. No way I am jamming something into the basket or using the cover bolt.
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GickSpeed wrote:
I use a rope to stop all my pistons; just like any other clutch I install. No way I am jamming something into the basket or using the cover bolt.
I have been known to use the rope myself. Others call it heresy. Seems like some sort of holder tool would be nice here for that kind of cash.
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sdjohn wrote:
I have been known to use the rope myself. Others call it heresy. Seems like some sort of holder tool would be nice here for that kind of cash.
jamming a screw driver into your clutch basket aint' so hot.
placing a clutch hook onto your clutch bolt aint' so hot.

using a rope is just an old school trick; uses much less ft/lbs then what your engine would deliver.

at times i just hold the clutch basket with my hand and use an impact on the nut; works as well.
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Liking the rope trick. Will keep in mind in case I have to revisit. Should be ok as I am, though, as long as I don't pull a Birdsnest and run the motor backwards.
⬆️    About 2 months elapsed    ⬇️
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First day in about 2 months when it's been both warm and dry enough to do some more experimenting with the 22 tooth cog.

It is a clear win in 2nd and 3rd gear. Max rpms unchanged, max speeds up a few mph, and rpms down a little when doing 40 mph in 3rd gear (typical for our many 30 mph zones).

It is mixed bag in 4th gear. While it is nice that rpms are down when doing 50 mph (typical for our many 40 mph zones), max rpms and max speeds appear to be down by about 600 rpm and 3 mph, respectively. I was under the impression I was topping out at 71 mph in spite of a 21 tooth cog. Now it looks like I was topping out at 71 mph because of a 21 tooth cog.

Will give this a little more time to digest, but probably headed back to a 21 tooth cog.
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Can you go to a shorter fourth? Probably could keep the 22 if so.
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Compare the max rpm in 3rd to the max rpm in 4th. If 3rd is 500rpm higher it's correctly geared.
Can easy talk you through adding more power if you want to keep the 22.
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Jack221 wrote:
Compare the max rpm in 3rd to the max rpm in 4th. If 3rd is 500rpm higher it's correctly geared.
Can easy talk you through adding more power if you want to keep the 22.
The rev drop is what has me mostly convinced I should go back to the 21 tooth cog. With just a hint of splutter, max revs in 3rd are about 8600 rpm using either the 21/68 or the 22/68 gearing. With the 21/68 gearing, revs go down to about 7800 in 4th—about an 800 rpm drop. With the 22/68 gearing, revs go down to about 7200 in 4th—about a 1400 rpm drop. Note that I still don't have a tachometer, so the above rpm figures are calculated, but I think they are reasonably accurate.

I think my results also breath new life into the original query: whether I might like a 20 tooth cog? For now, I plan to live with the 22 tooth cog a bit longer and see how it goes. For one thing, it was quite windy yesterday, and that may have influenced the numbers.

Call me a piker, but my feeling is this kit is so well conceived and executed, with the whole being much more than the sum of its parts, that it would be akin to painting a mustache on the Mona Lisa for me to mess with it.
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sdjohn wrote:
Can you go to a shorter fourth? Probably could keep the 22 if so.
Shorter 4th means 36 tooth T5 cog?

Again, call me a piker, but this engine is running so well right now I feel like I've caught lightning in a bottle. Splitting the cases again would just be asking for trouble.
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yeah, 36 tooth

I hear what you are saying, I'd probably not split it just for that, but keep it in mind the next time you go in or are ready for some major work. since you like what the 22 does for 2nd and 3rd but not 4th, i'm betting it would make 4th like it is with a 21.
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If LML copied the 125 / 150 PX EFL gearbox it should already have a 36 teeth 4th in there…
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SaFiS wrote:
If LML copied the 125 / 150 PX EFL gearbox it should already have a 36 teeth 4th in there…
AFAIK, regular Stellas have a 35 tooth 4th. There was a limited edition called the Fireball that came with a 36 tooth 4th, but that is not what I have.
@sdjohn avatar
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Johnny Two Tone
'15 GTS300, '86 PX125EFL, '66 VBB, '01 ET4
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Johnny Two Tone
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'15 GTS300, '86 PX125EFL, '66 VBB, '01 ET4
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Location: San Diego, CA
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my Stella engine had a 35
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Ossessionato
1997 Italjet Formula 125, 2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
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Ossessionato
@subetherbass avatar
1997 Italjet Formula 125, 2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
Joined: UTC
Posts: 4924
Location: Australa, Mate
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Kowalski wrote:
Shorter 4th means 36 tooth T5 cog?

Again, call me a piker, but this engine is running so well right now I feel like I've caught lightning in a bottle. Splitting the cases again would just be asking for trouble.
Sounds like you need to knock 2or3 teeth off 4th.... but what would I know? I only ride 8"
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Addicted
2005 Stellalossi 177 Fe
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Addicted
@kowalski avatar
2005 Stellalossi 177 Fe
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Location: MA
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Bit of an update.

We've had some pretty atrocious weather around here lately, but was able to do a little more riding with the 22 tooth clutch cog today. Looks like prior mediocre top speeds in 4th were, in fact, due to headwinds. Fairly calm today and top speeds in 4th were about 71 mph rpm on the flats (gps read more at times but trying to be conservative). Can't maintain that up much of a grade. All about the same as with the 21 tooth cog.

Calculated max rpm in 4th is about 7600. That is about a 1000 rpm rev drop, so still suboptimal.

Thinking I will have to try a 20 tooth cog if for no other reason than to get it out of my system.
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Molto Verboso
71' Sprint Veloce , 05' Vespa PX150, 1978 P200E
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Molto Verboso
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71' Sprint Veloce , 05' Vespa PX150, 1978 P200E
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whodatschrome wrote:
If you drop down from a 21 to a 20 tooth clutch, it's going to make your acceleration worst in 1st and 2nd gear, then hamper your 4th gear top cruising speed. The reason being is that the engine's powerband won't be able to match up correctly with your actual speed. It would be very inefficient acceleration since you won't be able to utilize the engines power. I don't know if that made sense to you or anyone else, or if i even explained that correctly. I did a bunch of experimenting with all sorts of clutch toofuses...20, 21, 22, 23, 24 in various P engines. If you want the absolute best transmission ratio for pretty much ANY sort of riding, touring, or racing (sidecars and offroad trail riding aside), then you would want a taller 1st and 2nd, keep 3rd about where it is, and a shorter 4th gear. Then match a taller clutch tooth count (depending upon cylinder) to complement it. My point is that i think a 20 tooth would make is suck. I'd install a 22t clutch instead. And if you don't want to ride as fast, then don't give it as much throttle. The same can be said about your current 21 tooth. If you don't want to ride fast, don't ride fast. But this is all from first hand experience and not from online calculators.
Amen!!
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Molto Verboso
71' Sprint Veloce , 05' Vespa PX150, 1978 P200E
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Location: Tucson, AZ
 
Molto Verboso
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71' Sprint Veloce , 05' Vespa PX150, 1978 P200E
Joined: UTC
Posts: 1614
Location: Tucson, AZ
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Kowalski wrote:
Koso Proton tachometer was garbage. Shipped with dead battery. Replaced battery and just showed gibberish above about 5,500 rpm.
I haven't used KOSO but I am using TTO and Runleader tachometers simultaneously and they are dead even within 10-30 rpms. I have a lot of pictures to prove it.
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