Modern Vespa

Hi!

I'm having some doubts and could use your help, please.

My PK50 XLS has what I believe it's called a long gearbox ratios. Instead of the usual (AFAIK) 10-14-18-22 input shaft, it has a 10-15-20-25.
I believe Vespas with 50cc sold in Portugal had this longer ratios, different from other countries.

It currently has a DR102 (Pinasco 102 on a near future), 16 gear cog, Del 19/19 and Sito Plus.
Runs just fine, around 70-75Kmh on the plain (GPS), +85kmh down hill.
The problem is at WOT it goes into serious high revs.

The engine is currently opened, doing some maintenance, and I thought I should change it's primary drive.
It original has 14/69 (16/69 with the 16 cog) and I thought, because everyone recommends it, I should go with a 24/72.
BUT, my bike has these longer gear ratios, so I believe it would not pull 4th.

What should I go?
18/67 instead?

Thank you for your help.

Regards,
Luis

BTW, my name's Luis Pita and I'm from Portugal.
Sorry for my username.

Cheers

Play with this for awhile
http://gearingcalc.free.fr

Thanks, scootermarc69.
I had already found that last evening, and it was a great help. Great tool!

I ended up deciding to go with the 21/76.

My thinking is: in order to the engine to make some serious revs, it has to have a good (sports) exhaust.
I have "only" the Sito Plus, and I'm not sure if I want to buy another one (and loose the spare wheel).
So, the Sito Plus favors medium-to-high revs (I think) but not very high revs. That's why I choose the slightly longer 21/76, on behalf of the 18/67.

Currently my PK does 70-75Kmh on the plain. From what I can see in the gear calculator tool, with the 16/69 fitted, it must be doing around 7500 rpm.
If I fit the Pinasco and a better crankshaft, I believe it will be able to pull the 21/76 at least up to the same 7500rpm, doing around 87kmh.

With a 18/67, to achive 87kmh, I'd have to go to a bit higher revs, and I don't know if the sito plus handles that.

What do you think?
Am I doing the right choice?

BTW: my PK50 gearbox has 10-15-20-25 and 58-54-49-44, not the usual 10-14-18-22 and 58-54-50-46.


Thanks,
Luis

Taller gears only give you speed if your motor has the power to push them. higher revving motors shine with lower gearing.

I had this right hand pipe for a PK I had thinking it might work with the spare but never got to try it to see before I sold the PK. I can say it looks like a nice made one with a true expansion chamber. If you try it please report if it indeed works with a spare tire. https://www.ebay.com/itm/163585409172?epid=1449349361&_trkparms=ispr%3D1&hash=item2616734094:g:04kAAOSw8VNcgk1g&amdata=enc%3AAQAGAAACoPYe5NmHp%252B2JMhMi7yxGiTJkPrKr5t53CooMSQt2orsSLY2M1Gjmuwt9c03vWNfiRlsUr6EUdpG%252BL32%252FZm%252BZBSzGS3CTF45bJop6YsNKmoLt829tHZXlHclRpJPxdqMhX37LCsiqMnq8ZE2PswAFpHbBO95gHnyiNuAFiA0nLI7qyX8wLW%252Bvv3k7XLdlDXjfkhHaKoCnlN%252BIh0W8BRJUpeaKchMl3OeoV%252B%252FHnzvx%252FHpiKwWVmdhOSwx2EHBoa7vUNcG%252FktwnIuv3ruBuaAvFzi7IQTi14tsWgcVt6GMSHAvLbcqxWqKeOh3ouQysRqKHk5mwhTZDtxg%252Bl%252BXgdJhHmEQl9L8BvldUTjtnUqwd4d1hqWC8r1kaPj5qF3VEENNctWIdb7phySLyL%252FNenBwn4t%252BjD6QB7HbxNt4I3Z0PwTGdm%252FIHtSLlCaqp5dcdrUFYChNQc7tNglUf82%252FYGXnllD2aV0a4EkQTD3PLiLYWFsqVixwjBlk9GrlkwSC6X7qcidrxvNSVUCVluDYHmgboI4tiZa%252BVYCAfKbjGz0wiKpy1CF6RJ%252FLQ3bmjpwJgrs%252BEmo5I69Y99piB0SHpB4%252F1Igsv0R95ouN5n6kBFV%252Fzx2iL%252FxRXd2JqSpwts91%252BQsqwiDGXbuZBNGPRE0EPTTZfhikocI5hvTN97nWcbnjrP8HZYeVfa7aCUR1C%252BC7qpwKV2onsyvu7Mt1rZKTzbpYdndqZ1qW2IPSmU1HNnk8BafY6mnwcvp5pgVGaPIfLNUvVXp1lMG7eYh7RZ6zTibP1sDyfDHYIgo1IpeVph2SxxLcxLa8OtDofZJelU8cmbB120QC%252B%252B5kvtAfx9usfHTxDYwtScaLytIzbHTnexnLLmvXZl%252FMtwXF1fbH6VTHoFWszxg%253D%253D%7Cclp%3A2334524%7Ctkp%3ABFBM2qi-0Oxf

Yes, that was my though.
With the Sito Plus my engine won't do many revs, I believe.
So I thought it would be better to try a taller gear, hopping it has the strength to push it enough to get some good (decent) speed.

Regarding the exhaust, I'd like to maintain the spare wheel, but mainly I would also like to avoid what I consider to be aesthetically not favorable on a Vespa. I may buy a better exhaust someday, but I have to like the way it suits.
The one you wrote may be very good, but I'm not sure if I would buy one.

Many thanks for your help,
Luis

This exhaust is better then the Sito plus. How much better???????
https://www.scooter-center.com/de/auspuff-bgm-pro-bigbox-touring-pk-vespa-pk50-pk80-s/xl/xl2/hp/ss/lusso-bgm1050pk?sPartner=bgm_de

rowdyc,

I'm not sure if I understood your question.

The question is how much better is the BGM over the Sito plus. I don't know but it's a newer exhaust then the Sito plus and it gets good reviews. May help with your power but again I don't have that exhaust on my PK. May try it if I ever upgraded to keep the same look as the stock exhaust.

Oh, ok.
I have no idea. They seem similar...

The flange and the box are slightly larger.
Test with a 125 parmakit and 19.19 carb says it's slightly better.
Torque seems about the same. Only 1 hsp more then Sito plus but it revs out to 6300 rpms vs the Sito 5600 rpms.

The best option and keep the spare of course is the right hand exhaust. The best stock look is the BGM box.

I have a pk 75 xl. It pulls average 49mph on GPS and is standard with original shbl 20mm carb . I changed out the sito exhaust as it vibrated through the frame awful although when taken off the baffle was loose. I have the bgm box tourer for 75 to 125cc and can tell you the following. It does not rev on like the sito but it has far more torque and you don't have to rev the crap out of it. The decrease in vibration to the whole frame is brilliant, no toolbox vibration, side panels, headset, the usual suspects. It makes the whole scooter extremely smooth to drive. You will lose 1 to 2 mph top end but you will power through when you have head wind or climbing slopes, hills,so its a far more pleasant drive and all round usability improved. Its a bit like going from a road 2 to polinibox on a large frame,revs drop but better torque . The bgm sounds great, its like a high pitched machine gun pop pop. Easy to fit,great finish, no corrosion as yet. Nice little touch is tail pipe points away from rear wheel so no crap builds on wheel. I've retained spare wheel too which is important to me. Upjet 2 pts , my standard carb 76 main so now bang on with 78. I recommend bgm over sito, if you want to sacrifice 2mph top end in trade for more diverse running and protecting longevity of your motor. Im also getting 120 miles to gallon! It will drop your revs down but give you a lot more oomph around town. Fastest I've seen with a tail wind is 52 mph 85kmh GPS and slowest I've recorded is 45mph with really strong headwind .75kmh. Enjoy the little pk for what it is, buzzing around local and putting smile on face. Every manifestation of bolt on exhaust ive used has always resulted in some compromise. Either having to rev the crap out of it to get anywhere and maybe couple of MPH over top end, or better early mid torque for driving into wind, hills, taking pillion. Always a trade off. I've attached the gear ratios from my manual, at bottom, gear 1,2, 3 then 4th

Thanks!

Thank you very much for your input!

I can only suggest you try one, it's about 100 pounds and if it's not for you sell it on or swap it back and forth depending what you are doing.you always find something different you like and don't like about exhausts but for this small capacity scooter the bgm for me is best choice. In my case nearly 50mph is amazing for a standard motovespa 75cc. I'm 6ft tall and 13.5 stone so hardly a lightweight

I took your point.

My questions was more related with the gearbox, being taller in Portugal than other countries (or so it seems).
Everybody recommends a 24/72 with a 102cc, or even a 22/63.
With the gearbox my PK50 has, from factory, it would be unusable. So I opted for the 21/76 DD.

I already managed to buy the Pinasco, anticipated crankcase and primary gear at a great price from a private seller, who happened to have all these for sell.
For now I'll mount it with the Sito Plus, 85 main jet and see how it goes.

It would be nice if it can cruise at 70-75km/h without going screaming all the time. Let's see.

Thanks!

Ive just read about the pinasco 102 and claims you can reach 90kmh on it, so hopefully your gearing will be good for your cruise speed you want. Most of the 102 kits suggest a 3.0 ratio, 24/72, so im not sure how your 3.6 ratio 21/76 will behave. If you are going to split your case etc, how much is a 24/72 primary? Would it not be best to try that first with the pinasco, rather than the 21/76. How good is your XL clutch, is it worth replacing this at same time so it doesnt slip with the extra power of pinasco?

Would the DRT short 4th christmas tree help with the 'long' gearing.

With the 24/72 gears, you can get a 21-25 pinion so can play around even more.

Thanks for your input.

Yes, 102 kit usually go with 24/72.
The thing is Vespas 50cc in Portugal have when out of the factory with taller/longer gearboxes.
If I fit a 24/72 in mine, it would be extremely long. 112km/h in 4th gear, at 8000rpm.
With the 21/76, at same rpm, it will do 93km/h.

If mine goes to 7500 rpm one the plain, I'm happy.
Let's see.

New clutch with reinforced spring.


Cheers,
L

Has far has I know, no.

Trees are usualy 10-14-18-22. DRT ones with short 4th are, I believe, around 10-14-18-21.
My PK has 10-15-20-25, so not compatible with DRT tree, because of the other cogs (z58-54-49-44).

21/76 is also DD, but I don't know if are other pinions, 20 or 22, for instance.

Anyway, 21/76 with my gearbox is similar to 24/72 with "normal" (short) gearboxes.
Let's hope I'm right.