rotary valve inlet timing on PE /PX range vespas

[drunkmunkey6969]

Al....you tried an M-Tech to help the low down jetting? They love to consume the extra juice low down? Just a thought, don't wanna 'teach grandma to suck eggs' etc

[sean brady scooters]

I ported my own Polini this way and it seems to do what the theory suggests which is increase bottom to mid range power with little in the way of over rev. This is because I knew the exhaust timing would be relatively low and also I wanted to pull taller gearing. It does 70mph at 6500rpm and has done 20,000 miles now so think its safe to say its a good mod.
I decided to do it after reading what Bell said about disc valves and just applied it to the Vespa.

Nowadays I tend to just flow and blend the port and just cut 10mm off the crank on most road going bikes. This is because I've found that before the bike goes onto pipe they are difficult to jet cleanly and get a decent tickover. To do this you end up running leaner settings but this causes problems when shutting off the throttle and coming back on from high revs. Couple this to people wanting autolube and std carbs and the benifits don't outway downsides for me. What I can say is when I overlay the graphs of my 207 against the 220s we do now the 207 boxes above its weight. But embarrassingly my bike has always been difficult to jet low down. I think next time I do one for myself I just won't go back so far and try and get a compromise.
On small block motors the inlet is so small that I often cut backwards to increase timing but still pull taller gearing.

just want to clarify with you Al ,did you open the inlet upon transfer closing time or a bit before that perhaps ...like i say i have never tried it before at all ,but like you have found that it really helps retain bottom end torque and power to do so earlier than usual

[Diablo]

I've got it all written down somewhere Sean. I'll try and remember to dig it out and let you know.
Dan yes I have thought of using M-tech but keep selling them to dyno customers before I get a chance!

[sean brady scooters]

thanks Al

[joeythescooterboy]

Just a quickie on the Polini kit,

do they come in 2 versions, one for standard stroke and one for 60mm?

I only ask as some may remember a while back my piston dinintegrated. Standard crank etc and I had 1.3mm squish.

Bought new kit from Beedspeed and ended up wit 2mm squish??

Had this before when I changed a piston on me mates (Sean and Dan sorted it a few weeks previously prior to a H4H trip to Africa..... it's in an old thread,) and with the new piston he ended up with .5mm extra squish? Took piston out and measured, it was actually half a mm shorter from top of gudgeon pin to edge of crown.

[jonny snatchsniffer]

on the smallframe its easy to open it before, so the inlet is open the same time as the transfers, on mine i run 140 BTDC and 75ATDC, tho id say you would need a pipe to take advantage of all the ports being open

[drunkmunkey6969]

on mine i run 140 BTDC and 75ATDC

Am liking that.

What pipe do you run?

[jonny snatchsniffer]

im using a franz, as im sure you know the fella that makes them is a bit of a rotary inlet freak so it works well, nice spread of power with a hefty kick up the arse at 6500, revving out to 9500+

[drunkmunkey6969]

im using a franz, as im sure you know the fella that makes them is a bit of a rotary inlet freak so it works well, nice spread of power with a hefty kick up the arse at 6500, revving out to 9500+

A franz? Nope....who is that?? Sounds like a fruity pipe.

[jonny snatchsniffer]

its made by a german fella called mathias scherer (amazombie on gsf and smallframe forum) its this pipe http://www.scooter-center.com/product/7 ... epaeckfach
he does quite a few smallframe pipes, and his race bike is a 29hp rotary cast iron polini, he does pipes for lammys too
similer spec to mine however are making 22-24 hp