Pros and cons of a 22 tooth primary on a kitted P125?

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hat
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Fri Apr 06, 2018 10:39 am

P125 with a pinasco 177, 24mm carb, fast flow tap and SIP road2, everything else standard. Its topping out at around 60-65mph at around 6500rpm. Would switching from 21 to a 22 tooth primary add much more, or would it lose anything?

ricalnic
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Sat Apr 07, 2018 12:23 am

Scooterhelp gearing calculator may help you in your decisions

http://www.scooterhelp.com/tuning/vespa.gear.calc.html

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drunkmunkey6969
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Sat Apr 07, 2018 10:46 am

If you are certain it will pull the gearing, then it will extend the top speed.

If it can’t pull the gearing, it’ll be ‘flat’ in 4th and be a pain uphill and into headwind.

shocky
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Wed May 09, 2018 6:24 pm

I'm building a 177 26mm carb
Either a sip2 or polini pipe and p2 primarys

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Shaunbond
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Wed May 09, 2018 9:34 pm

I run a 22 on a standard 150 without issue, still pulls well up hills and into headwinds. Sito+ exhaust so lower torque curve helps.
Also run a BGM 177 with 23\68 gearing which is a fantastic cruiser without loosing too much low to mid range.
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Muttley McLadd
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Wed May 09, 2018 11:14 pm

Does it make good torque?
My 190 runs a 60 mil crank - not sure how much difference that makes - but similar spec to yours with the 24 mil carb and SIP box pipe. It pulls 23/65 (short fourth) with ease. Two up too.
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Thu May 31, 2018 5:24 pm

I'm also presently building a "quick" engine using a Polini pipe, cut crank, malossi 166 with the casings matched, and a 24mm carb.
Was a bit miffed about gearing but finally opted for a 22/68 primary through a late model 150 gearbox. Going for nippy round town use as opposed to motorway cruising. It was a toss up between this and the P200 23/65 primary drives. Previously had a 177 Polini in the same set up with the Polini 23/64 primary drives and it just wouldn't pull it - and that was with a 28mm delorto PHBH hence my decision to go 22/68.

Hope this info is of use.
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Lukemx82
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Wed Jun 13, 2018 3:54 pm

I run a cast iron polini 177 si24 carb and jl lefty and have upped mine to 22 primary.

I did it more because I wanted to bring the revs down a little bit when cruising in 4th at 60mph for long periods and it did the trick. It pulls the gearing fine with 2 up to that speed.
Dont often want to go faster than that but it reaches 70mph (on the speedo) easy if I leave the mrs at home.
With two up on the 21 primary there were always moments when I had to drop it to third to get up a steep hill but now with the 22 if I do have to drop to third its a bit taller also so probably still maintaining the same or higher speed hitting hills.

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