Modern Vespa

This is one of the many responses to your quote. How do you manage to achieve 75.4 mph on a GPS? I ran ran my PX150 on a new Malossi aluminum 177cc, 26 /26 carb, SIP 3.0, tucked down on a 22 cog clutch and after almost a mile being tucked down at 8170 rpms I only saw 66 mph(GPS). From 66 mph to 75.4 mph there is a huge different, in terms of rpms is got to be around 1000 rpms. How is that achievable? what were your rpms? I am roughly 200lbs and I was on a confirmed verified flat road with less than .075% incline and I am at 2400ft altitude

To the OP,

Responding to your first comment. How do you get 50mph in second? by any chance are you running the P200E gears, maybe someone put the fireball engine on your Stella (Fireball came with longer gears).

I have a LML (Stella engine) on my sprint veloce and I have a PX and I am no were close to 50 MPH in second gear. I could get closer to 50 on the P200 riving the hell out of it though.

As far is the reference from scooter help on the gearing calculator don't rely on that as more and more people with instrumentation are proving that the speeds, rpms and gears don't really correlate that well.

You are not going to like the 20 teeth clutch cog. It is way too short. It limits your top speed at hwy because you will be doing 64 mph at 8100 rpms(that is what myPX does). Acceleration is OK but it dies off so quick on the top end on the first 1-2-3 gears. Basically your engine wants to keep pulling but you are killing the acceleration because you maxed out the rpms too quick, similar to rally cars when they change the final gear ratio and the can accelerate to fast but not with lot of top speed, in this case the PX150 /Stella with a decent cylinder kit can keep accelerating but due to short gearing you are limiting the performance.

Go minimum 21 cog.

The 75.4 mph was a bit of an anomaly. As stated, it was on a bit of a downhill. May also have been a tailwind. May also have been getting a tow from car in front.

Normally can do about 71 mph (gps) on the flats. Can't maintain that up much of a hill. That's at a calculated 7800 rpm with the 21 tooth cog and 7600 rpm with the 22 tooth cog. Motor is a Malossi 177 cast iron, on matched LML reed cases, Worb 5 flowed crank, Boyeson reed mod, Malossi box. Altitude a wopping 75' (LOL). A little lighter than you, but i do not think weight matters. At these speeds, it's all about aero drag.

As discussed with Jack221, the 50 mph in 2nd probably was because I was running too lean and revving over 10,000 rpm. Back down to max 8600 rpm now.

I have a regular Stella which AFAIK comes with a stock P200 gearbox (35 tooth 4th). Apparently the "Atomic Fireball" version comes with an EFL gearbox (36 tooth 4th).

Let me know if you still have a 20 tooth cog you'd be willing to donate to science. I'll pay shipping.

I know it nitpicky, but no LML scooter came with an EFL gearbox. Yes, the transmission bits can be interchanged with Piaggio bits. "Same same but different" is how i would politely describe the differences between the two. And the Atomic Fireball was geared higher, not lower than the standard Stella. The idea was to make it have a faster top speed by installing a taller P200 primary (23/65), which it did...down a steep hill.

I'll save you the postage. Pre covid science said the 20t clutch sucked. Post covid science says the same thing. The 125cc T5 came with a 20t clutch and that engine was all about high rpm. Kit the T5 with anything and you automatically have to bump up to a 21t or even a 22t clutch. I know you're curious as all get out, but you'll just have to take everyone's word for it. And yes, i experimented with a 20t clutch in my P200 track bike. It sucked. I removed it at the end of the practice day on saturday, then reinstalled the 23t for the race on Sunday.

I'd split the cases everyday and twice on sunday in order to install a shorter 36t 4th. Tall 1st, tall 2nd, standard 3rd, short 4th for the win. It would pair VERY well with your 22t clutch. Spend the 30 minutes to split your cases, then another hour to reassemble. Done and done and the results would be a happy Kowalski.

I can't imagine how a 20/68 wouldn't scream it's nuts off at the speeds you're describing. I'm running a 22/68 in my Stella and it feels about right. I'm considering going up to a 23t.

But give it a try. The butt dyno will tell you whether it's an improvement.

What takes you an hour and a half would take me a week and a half. Could be a project for next winter though. So short 4th means 36 tooth gear. In terms of tooth count, what is a tall 1st and a tall 2nd?

Well, the whole point of the exercise would be to rev higher in 4th. If max rpms are 8600, and I get 7600 with the 22T, and 7800 with the 21T, then it seems plausible that a 20T would put me closer to the target 500 rpm rev drop.

In the lower gears, 8600 max is still 8600 max. The only thing that really changes is I would be upshifting at lower speeds during casual riding: say from 2nd to 3rd at 30 mph instead of 35 mph, and from 3rd to 4th at 45 mph instead of 50 mph.

Because the gearing calculators cannot account for wind resistance, calculated speeds above about 60 mph are just hypothetical. When you're talking about 70 mph plus, I think you need to get out there and actually try something to know if it works.

I can't remember what the tooth count is for the DRT long 1st and 2nd gears. But unless you're wanting the absolute perfection in gearing, then keeping the stock 1st, 2nd, 3rd would still work excellent with a 36t 4th.

My trick for a quickly splitting the cases is to have ALL my tools laid out and ready to go. Plus all the materials (cleaner, sealant, shop rags, paper towels). Also have the replacement parts ready to go as well. If you know exactly what parts you need, order them up a couple weeks beforehand.

To swap in a short 4th,
-remove the head,
-unbolt the selector box,
-remove the two long head bolts on the right hand side case,
-separate the cases,
-remove large circlip from gear stack,
-slid off the original 4th gear,
-slip in the new short 4th,
-reassemble cases,
-ride with smile on face while shifting from 3rd to 4th gear.

I am not sure that you can fit a 23. I have a spare Clutch cog with 23 teeth and I couldn't physically get it in to line up. It wouldn't mesh on my 05 PX150. Hopefully if I recover from my fall from 11 days ago I will work on my PX150 again to install the 21. I should be able to try the 23 for you. I have on hand a 20, 21, 22 and a 23.

I concur

I understand your theory about wanting to rev up more but the engine will overheat in no time. With the 20 tooth gear the high speeds are not feasible or sustainable. With the nice mods that you have you should be only with a 21 or 22 clutch cog or even a Malossi overdrive. The 20 clutch cog will be maxed out so quick. Are you running a CHT gauge?

engine speed = engine speed no matter what MPH it happens at. gearing just changes the MPH it happens at. some minor difference in air flow but not much.

if your engine overheats, it's not from gearing. it's from poor jetting. or a bad fan. or bad airflow. but not gearing.

There are 2 sizes of 23 tooth cog. A 40mm one for the 68 and the 42mm one for the 65 gear.

True on the jetting but I was talking about sustained high rev speeds. The Jetting can help but you are still going to generate a ton of heat and eventually the CHT is going to get very high. The OP wants to go nuts and ride well above 8000 rpms for sustained periods. I personally don't recommend it and I am firm on my opinion that it will generate a lot of heat at that RPM range. I have done 1 hour sustained speeds of about 60 mph but that is no where close to riding above 8000 rpms. If someone can ride above 8000 rpms for a long time I want to know the formula, seriously, I want to know.

Good to know. What I have is most likely from my P200E because I went from a old style clutch to a cosa style clutch and what I tried is the P200E one. What you said makes sense. Thanks for pointing that out, I was not aware that there were two different 23th clutch cogs. The 40 and the 42mm would be the diameter of the cog gear I would assume? If that is the case I can go and verify that. I am learning something new everyday.

A correctly set up 2 stroke will run full throttle at stable temperature until the fuel runs out. The mechanical stuff and the ignition timing are fairly straightforward. It's always the jetting.

After noodling on this some more, I have concluded the hive-mind is correct and a 20 tooth clutch cog is not worth pursuing. I believe it would raise max rpms in 4th to something in the range of 8100 – 8200. The problem is even 8200 rpm is not enough to overcome the higher final drive ratio a 20t entails. The net result likely would be the same 71 mph top speed I am getting already with the 21t and 22t. Nothing that would justify the 20t's shortcomings in the lower gears.

Pulled the trigger on a 21t to use for the upcoming season. Recalculated max rpms are about 7900 (I was selling myself a little short before) so rev drop is 700. Close enough. Will revisit using the 22t with a 36 tooth 4th gear once the season ends.

^^ Very smart choice by going with the 21 teeth cog. Your top speed of 71 mph vs my top speed of 64 mph. I only managed 64-65mph at 8100-8170 rpm and that was tucked down for 1/2 mile to a mile. Doing 71 mph would have been closer to 9000 rpms. Do you have a tachometer at all? my 20teeth cog just wouldn't go over 64 on either the Malossi 166, Malossi 177 aluminum kit, or the Polini 177 cast iron Kit as tested within the last 2 months. I would hardly get it above 8000 rpms and I have a 26 carb and I tried the Polini box and SR3 with bigger jetting. My engine case is not ported nor I have the reeds because it is a PX150. Either way, you will surely benefit from the 21 teeth cog.

The only time I see beneficial on a PX150/ Stella to have the 20 teeth cog would be on stock power(untouched), that is when you need the most aid from the gearing to get it up to speed.

I am about to put a 21 cog myself, my hands finally recover from the accident from 16 days ago. I tried the 20(that is what my PX150 had) then I put the 22 and I just purchased a 21 a couple of weeks ago.

You've probably asked yourself, how much "modern clutch nut" torque is too much "modern clutch nut" torque? Well, I have your answer.

Was riding along minding my own business Sunday when shifting started to get stiff and a vibration set in at higher rpms. Recalling that I had some concerns about whether the clutch nut was tight enough, it eventually occurred to me that the clutch nut was coming loose. Looked into it today and that was indeed the case. No big deal. I was planning to install the 21 tooth clutch cog anyway. Plus, I now have the world's only VMC 10 molle clutch with a custom machined finish.

In the meantime, I had realized that, even though the VMC does not accommodate a clutch holding tool, I could just use the flywheel holder on the other side. So, upon reassembly, I said to myself, "self, this nut isn't coming loose again," and I torqued that sucker up to about 70 ft/lbs (100 Nm). And there it sat for about 3 minutes, until I heard a crack and watched the nut explode into 3 pieces.

Going to order a couple more nuts and try 60 ft/lbs (80 Nm) next.

Too much torque on that nut won't just damage the nut (or destroy in your case), but can also damage the thick spacer washer/mixer gear that goes between the clutch and the crank. It can also damage the clutch baseplate as well. When either of those get damaged, then the brass bushing gets messed up...then a whole bunch of collateral damage can happen. Keep in mind that stock spec is 28-32 ft/lbs. You're better off using a lockwasher and some red locktite to keep that nut in check. Or even a plain ol' M12 lock nut that you can get at any local hardware store (as long as you can fit the socket and nut through the clutch to tighten it).

Sometimes you gotta do these things.

Once you work out which setup is BEST for staying on the powerband in 1-2-3 gears, THEN you need to start taking teeth off 4th till its on powerband ALL THE TIME!

Oh my I'm sorry dang it but you have a good attitude much better than I might have had and your story reminds me of something that happened to me recently. I was over at my dad's helping him adjust something on one of his gates. I was tightening up a 1/2" galvanized bolt and was in the midst of saying I didn't want to overdo do it and before I could finish saying that we heard a pop. We just laughed and it will be one of those memories I will keep forever haha.

I'm afraid that with that much torque you might have also twisted up your crankshaft, since all that went through your big end. I'd split the engine and check the trueness of the crankshaft with dial indicators.

The 30 ft/lb spec is for a castle nut and basket washer with a folding lock tab. I think it is pretty clearly inadequate for one of these so-called modern clutch nuts. Can't find the posts now, but I have a recollection of people here saying they were going as high as 60 ft/lbs. Maybe try 45 ft/lbs plus the red Locktite?

A reasonable concern. I assumed the crank could handle it. Time will tell, but will wait until I am symptomatic before splitting any cases.

https://modernvespa.com/forum/topic176645#2494878

This is the thread I was thinking of.

SaFiS says flanged nut + 60 Nm (45 ft/lbs) + Locktite.

jack221 says flanged nut + 2 foot breaker bar done up "pretty tight" + Locktite. Based on my use of a 2 foot breaker bar yesterday, I estimate that "pretty tight" gets you to 50 ft/lbs at the least.

this is a real concern

if you don't have a clutch holder you can use rope in the cylinder, at least then you aren't twisting your crank halves in opposite directions

Not sure how tight this was, but it held!

Yikes! Maybe clutch is fine?

I remember that one. how could we forget it??

It's definitely twisted, 100nm is a hell of a lot of force… it's driveshaft torques…transferred to the other side.

Just depends how much it's twisted.

The crank webs shift with taps from a copper mallet…

After an unusually pathetic performance by UPS, new clutch nut arrived yesterday. Delay was excruciating because I've been in serious, "I gots to know," mode ever since the folly of using the flywheel holder to torque the crap out of the clutch nut was pointed out here.

Everything buttoned back up with 21 tooth clutch cog. Used 45 ft/lbs, rope trick, and red Loctite. Hopefully that holds.

Clearly, using the flywheel holder to torque the clutch nut to 70 ft/lbs was not one of my better ideas. Nonetheless, the scoot still runs ok. Can't really tell whether there is any new vibration—if there is, it is subtle. Performance in the various gears is the same as seen with a 21t cog in the past. Planning to run it as is for the rest of the season. Reasons to split the cases again are mounting, though, so it looks like that will be a winter project.

Update--20T clutch cog on the way.

New impetus is conversion to oopsclunkthud bellmouth and Uniflow air filter. Initial impressions of that were a bit, meh. Having lived with it for a while, however, it is clear my max revs in 2nd and 3rd are up about 500 rpm to 9,000 plus. Max revs in 4th are still a little under 8,000 rpm, so drop is pretty bad. It now seems plausible that going from 21/68 to 20/68 gearing can get max revs in 4th up to around 8,400 rpm, which would be enough to yield a tangible net gain despite the higher final drive ratio.

Most economical option was SIP via Mercato, so likely to be a couple of weeks before results are in.

Well, you had to (have to) try it. There's no real substitute. If it doesn't end up doing what you expected, at least you will have learned something.

I went back and forth on installing a short 4th on my 200. I don't really mind the gap between 3rd and 4th, but it sounded like it would help a lot for the hilly riding I do. Had to split the case anyway, so why not? Just have to try it for myself. My next build is with a Malossi 200 kit. I have a short 4th for that one too that I will decide on depending how it goes on the stock 200.

Btw, I have been waiting for a clutch cog from SIP (through Mercato) since 6/21. It just shipped earlier this week.

Finally had a chance to get the 20t clutch cog out on the freeway. So far, I am not seeing the results I had hypothesized. As expected, top speeds in 2nd and 3rd are down about 3 mph compared to the 21t cog. Contrary to my hopes, max revs in 4th have not gone up at all, and rev drop from 3rd is still about 1,000 rpm. With the higher final drive ratio associated with the 20/68 primary, that means top speeds in 4th are also down about 3 mph (i.e., 68 mph).

Scoot still rides great, and I have found it pays to live with these kinds of changes for a few weeks before drawing final conclusions, so will leave the 20t cog in for a bit. Nonetheless, preliminary conclusion is that this motor simply cannot pull more than 8,000 rpm in 4th regardless of gearing, and I will be going back to the 21t cog.

Glad you tried it. Playing with gear ratios was something I wasn't even aware of back in the 80's. It can completely change the personality and ride of a scooter and there are so many possibilities. Changing the primary is not as quick swapping out a clutch cog, but still not that hard. Even better to have more than one scooter. 68mph is not too shabby.

I love how the 22/68 on my Stella pulls hills and how quickly it accelerates. The 23/65 in the 200 makes it feel more heavy and cruisey. I can't wait to try it now that the short 4th is in.

Good idea to ride it for awhile as different doesn't always seem better at first. I didn't like the 200 much at first. It felt sluggish at first, but I appreciate it at highway speeds.

Which it was as easy to drop a taller final drive gear into an old VW 3 speed auto.