Polini 177 + Sito Plus...need more speed

Hi All,

I recently purchased a PX 125 disc from MSC with Polini 177kit and Sito Plus exhaust fitted…I get top speed 65mph…cruising speed just over 60mph.
I would like some more top speed without changing the carb or any engine modifications so I was wondering if I bought a SIP performance exhaustPM or a scopion would this change add more top speed and maintaing the torque from the Sito Plus.

Regards,

Brian.

Greetings Brian , with regard to your question, defitnitly you will gain more top end speed but will sacrifice a bit at low end , but , remenber to re jet your carb . and also the sound of the exhaust might offend you you may also check my bulletine board post under the title, acceleration fron sip exhaust - by chen, you might get a few tips

long live the wasp

chen
[:smile:]

ditch the shito plus and get a midrange pipe like the simonini,a sip pipe needs more power than just a cylinder kit can kick out
you want power??? polini gear up kit & dellorto 28mm with that barrel+piston will give you at least 70-75mph or the cheap option find a second hand px200efl gearbox to put in it

Hi Goran,

Thank you very much for your reply…I hope you can help me with some more questions…

You recommend the p200 carb but if I decided to just go for premix what is the best bang for buck carb you would recommend?

You mentioned the inlet ports…I don,t think I can get someone to do this for me…If I cannot, can I go ahead and add the carb and Polini gear up kit and still expect to reach 70- 75mph?

I was tinkering with the idea of getting a Polini exhaust since the Cylinder kit and gear ip kit is Polini…do you think the Polini pipe will do a good job of cooling?

Thanks for your kind help.

Regards,

Brian.

exactly the same set up as yourself, had nothin but probs! t5 carb, octainbooster, anything over 5half thous revs pinked its nuts off as everyone on this board nos! dont run autolube, run 3%!!! infact give it up and get pinasco 177 kit, superior! not as powerfull as polini but a lot more reliable. not runnin anyone elses opinions down, its just my own opinion[:drink:]

I read your post with interest:

So if I just buy a Polini Upgear kit and say a Scorpion pipe this will be enough to get me to 70+??

I would like to keep my existing carb cos the autolube but if I don’t change it will this become a bottleneck??

Also if I add these goodies is there more change of the Polini kit seizing?

Regards,

Brian.

Oh yes. No problem. Your engine should be able to pull the bike up to at least that. About 75 mph is the theoretical top speed with that gearing. I don’t think you will need the Scorpion pipe, as a matter of fact I think the Sito will be a wiser choice, since it has a broader powerband (read: easier to pull the gearing at lower revs). Also, it is much more quiet than any real expansion chamber.

You’ll loose some of the hp at higher revs with the Sito, but you will get a bike that is easier to drive around town/at lower speeds.

Running the Polini 177 with the original carb is not advisable, especially not with an expansion chamber fitted. (Hot, hot!) Consider fitting the SI 24/24E (Piaggio original from the P200) to get enough cooling at higher speeds. You can keep the autolube, the carbs are identical except for the increased size. The original inlet (not the carb) of the PX125 is a huge bottleneck, by enlarging the transfer ports to suit the Polini 177 and widening the inlet by 2mm front and back you will get a really feisty little engine!

People are often referring to the Polini 177 as seizure prone, but I think different. You need to run it in very carefully (at least 900 miles/1500 km), set the ignition dead on 19 degrees and make sure the carburation delivers enough fuel to cool the piston crown properly (read: at least 24mm). Also, fit a NGKB9HS or equivalent heat range spark plug. If carried out, the Polini 177 is as reliable as any other tuning cylinder for the PX125. By using an octane booster, you get rid of the pinking/knocking which can be a problem when running at higher revs. Not all Polini 177’s have this problem though.

Good luck!

/Goran

Original von pyperb: I read your post with interest:

So if I just buy a Polini Upgear kit and say a Scorpion pipe this will be enough to get me to 70+??

I would like to keep my existing carb cos the autolube but if I don’t change it will this become a bottleneck??

Also if I add these goodies is there more change of the Polini kit seizing?

Regards,

Brian.

I hardly think you will need a bigger carb than 24mm if you choose to leave the inlet and transfer ports untouched. If you do decide to buy a bigger carb, the DellOrto PHBH 28/30, with the polini or Malossi slide inlet is a good choice. Not much use if the engine isn’t prepared for such a big carb though.

You will miss out on -a lot- of power if you decide to leave the inlet and transfers untouched. I would estimate the diff between untouched and ported to be around (at least) 5-6 hp, so you might want to find someone with a Dremel… I think you will get to that top speed anyway, but I wouldn’t think the engine will be powerful enough to hold that speed through uphill and wind. (You’ll find yourself doing the 4-3-4-3-4-3 gear dance.)

Steer clear of the Polini! It’s nothing but a high rev noisemaker, and since it contains baffles inside the chamber, it isn’t even a real expansion chamber. The Simonini is not good, but a heck of a lot better than the Polini, IMHO. Should you wan’t to buy a real expansion chamber, go for the Scorpion, JL or PM pipes. They have a broader power band, and a much higher top hp output.

Bye now!

/Goran

Original von pyperb: Hi Goran,

Thank you very much for your reply…I hope you can help me with some more questions…

You recommend the p200 carb but if I decided to just go for premix what is the best bang for buck carb you would recommend?

You mentioned the inlet ports…I don,t think I can get someone to do this for me…If I cannot, can I go ahead and add the carb and Polini gear up kit and still expect to reach 70- 75mph?

I was tinkering with the idea of getting a Polini exhaust since the Cylinder kit and gear ip kit is Polini…do you think the Polini pipe will do a good job of cooling?

Thanks for your kind help.

Regards,

Brian.

Maybe you need to check your timing, pinking is pre ignition, either the piston is too hot from not enough gas and air mixture so maybe check your plug colour or the timing is wrong and firing in the wrong time, check your timing pref with a strobe as the higher the octane it changes the time it explodes, also maybe run a cooler plug

There is no way you can get the PX125 to go any faster than that, unless you either make it rev MUCH higher or install a higher primary gearing.

At 60 mph (your crusing speed) it is already at around 7000 rpm, and at the top speed of 65 mph it is at 7500 rpm.

The Polini cylinder is designed to deliver its peak hp at around 7000, so don’t expect it to rev any higher than it already does. The Sito Plus is designed to work best at lower revs, which won’t help you either.

Lets say you want to reach 75 mph top speed. With the original gearing, the engine would have to rev up to around 8500 rpm. With an upgear installed, it would only have to rev up to 7000 rpm to reach that speed.

Anyway, if you don’t mind experimenting, you could lathe off 1.5mm from the top of the barrel, and putting a 1.5mm shim under the cylinder, changing the port timings to get a -much- more rev-happy Polini. At the expense of loosing the bottom end power, of course…You won’t have any problems reaching 8500 rpm with a JL or PM pipe installed with this technique though.

/Hedge