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Help setting up SR 172 Malossi ported!!

Hi i am form england and have an aprilia sr 172, wich is the engine with the nut on out side of the casing. I am having problems getting the most out of my bike i think my rollers may be too light but i coloured variator with pen and it wore away all of the ink so it was showing me the belt was rising to the top, how ever it only goes 80mph :(

here is my set up:
ported malossi 172 kit
pm tuning exhaust
26 phbl dellorto carb
polini variator using 11.5gr rollers
polini belt
pm reed block
and pm tuning race crank

i did have a gear kit and 16gr rollers but i didnt think it was very good accel, i raced my friend with runner 172 and took me untill 60 to over take him, so i took the gear kit out and am currently running 11.5 gr rollers, it seems like its fast, but thats only becasue i think the rollers are too light, and like i say it only does 80mph!
when i had 16gr rollers and gear kit in i dont think it was much slower accel if anything its either slower or the same wich is confusing PLEASE SOME ONE HELP ME!!!! :)
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Hi have got standard gearing in now, and going to get a gear kit and a 34mm power jet koso carb. what do you think on that?
i would gear up back in now with the light rollers , while your doing get some stiffer clutch springs aswell as this will help on pull off , also i wouldnt buy the 34mm koso carb as it is overkill on your engine 28mm koso max , good luck .nick

What about the dellorto phbh 30mm?
and scooter attack say they use 35mm keihin
and scooter center use a 33mm keihin

i want max performance i see the 70cc with 28mm so would 30mm be too big?



New Member
Hi Im new here! :L

My friend has an sr and I have helped him to set it up.

Differences from your sr are:

Malossi variator and belt.

Jolly moto for malossi cylinder.


I have no experience of a polini variator but I have tried the polini 180 belt and I dont like it. It is longer than a std or malossi belt and gives all over lower gearing which means that you loose top speed. If it is the 180 polini belt you have I think you should get a shorter one and get a higher top speed.

It works with 180 gearing and std variator but since you use the low 125 gearing you wont need it. If you still has std clutch spring get some malossi ones. The green ones are probably hard enough.

I think a jolly gives the power at higher revs than a pm so it needs heavier rollers. My friends sr has 14,5 g in his multivar so my guess is that you need heavier rollers than that. I cant tell you what weight you need so you will have to try a lot of different weights. You can mix different weight rollers to get more alternatives.

A pwk is a much better carb than a phbl or phbh but a 28 mm might be too big for your set up but try it and see how it performs.

How is your dellorto set up now?

Hi thanks for your reply.
PM tuning reccomended ther polini variator as they say it works very well
its a polini belt for 125 or 180.

And im running 11.5gr rollers and goes very well, i was clocked by my dad at 88/89 mph.

I am getting gear kit, and putting my keihin 28mm pwk on today.
i will let you know how it goes.

and i have seen the malossi rear torque driver, do they make a difference?

also im using a 115 main jet on 26mm dellorto...?
i would also get a malossi mhr manifold or simular one as i dont think the pwk will fit on the standard one , also what about a malossi cdi as that could give some more power , and the reason some 172 s use 30-36 mm carb is theyve had the reedblock opened up for 85cc motox reedblock so they can get much more flow into the casings. i no the malossi torque drive is very good on piaggio 50 engine , so i expect its not to bad on the 125 engines .

i have manifold that fits the pwk cant decide what reedblock to use.
i was thinking vforce reedblock, also was going to get cdi but only found malossi cdi for gilera runner and it says it doesnt fit sr.
ive got a polini clutch now with green springs pulls away alot better :
whats the best reedblock money can buy for my bike then?
There are two polini belts. 248.039 is for 125 and 248.018 for 180. The number is printed on the belt.

I used to have a stage6 v-force 3 in std piaggio size and it was good but I think the carbon petals in the stage 6 version is of a lower quality. Now I have kx85 tassinari v-force 3 and they seem to last better.

A 115 main is probably fine in a 26 mm carb depending on how thick the tip of needle is. In a phbl25 a 40 slide and a aq268 atomizer are a common set up. I have reached the best results using needles with 20 mm or longer taper and a thicker tip like a d36 or x25.

ok well i will get the vforce hopefully will work well, unless there are any better reedblocks out there?

pwk 28mm will be going on tomorrow.

gear kit is on its way.

what else can i do :p


Need tuning? PM!
Loose that 26mm Dell'orhto, total crap and hard to adjust. Get an 25mm, worsk allways, doesn't matter which jet you put in.

You won't be needing a bigger as 25mm. Those 172 engines don't make alot of revs and a 30+ mm would be totally not adding preformance.

Those high end 70cc kits scream upto 14,500 rpm, meaning less time to fill the cylinder, which means bigger carb.

The 28mm pwk has got a auto lube nipple, but i will consider pre mix.

Does any one know what is ment to be the best variator? Malossi or Polini.
What is the best reedblock?
And does the malossi torque driving work very well?

The 25 mm dellorto phbl is the same carb as the 26 mm no matter if it is a phbl or phbh.. And yes they are both crap for a tuned engine.

Total stroke on the oilpump is ~28 from std setting to bottom out. When using a 25 mm carb you can adjust the oilpump 3 mm ahead of the carb but with a 28 mm you have to adjust it to std setting.

This is not enough oil for the engine because it uses more fuel than it would with the std carb. If it runs rich you will have even less oil %.

So will i get more power pre mixing?

Also what is ment to be the best reedblock as i am wanting to buy one!
also do the straight manifolds give more power?


Mavio.. going back to belts and variators ive just checked up and im using the 180 polini belt on polini variator.

How ever im getting my gear kit fitted in the next few days what is the best belt to get? Can u mix malossi and polini.

Also when you put a gear kit in a scooter what is the moto, do you tend to need a bit lighter rollers? or do you leave them as they were?

Higher gearing need lighter rollers.

With a gear up its probably ok with the long polini belt but if its fast enough of the line with a shorter one it will have more topspeed. Try all combinations.

You can fine tune the vario to compensate for different width belts using shims instead of or together with the 1 mm washer between the outer pulley and vario.

Go for the v-force 3 from stage 6 that fits piaggio engines without mods. It is very cheap for a v-force 3.

Pre mix will not give more power but keep your engine alive.
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