Modern Vespa

I have had a 2005 U.S. PX150 for a few years and after ditching the catalyst pipe for a Road 2 and messing with the jetting forever and drilling the fuel passage and installing a high flow fuel tap, I have had it running great for a couple of seasons. Well as great as a 150 with stock piston, cylinder, head and porting can run. When I ride it, I try not to rev the living sh#t out of it, but in 4th gear running at speed, it gets up there (not sure what "up there" is without a tach, but it's revving). My question is can this motor be run at whatever revs it can reach? Does the piston port design limit the attainable revs to a number the motor is designed to withstand, assuming correct jetting and a healthy plug reading? Or should I be backing off when it feels like the motor is turning a lot of revs?

2 strokes limit their own revs on the port timing. With a stock 150 the limit is the piston rings at about 7500 rpm. Stock timings will be lucky to make 7500 rpm, even downhill. So, go for it as much as you like.

Road 2.0 pipe loves high revs, floor it and see what GPS speed you get, wouldn't be surprised to see genuine 60mph with that exhaust fitted.

I've owned 4 different 2005 PX150's. I love everything about them except for their absolutely gutless engines. Stock, the top speed is about 47mph. I'm a bit skeptical that any bolt on muffler will increase the top speed to 60mph on any flat road. A Sito+ gets the speed up to right about 55mph.

More torque can be found from matching the stock cylinder to the cases as well as matching the carb to both the airbox and case.

I would never run an air cooled motor to the absolute limit it can reach for long durations. A quick burst, sure. But WOT for more than 2 miles and I'll back down. If I need to cruise for a long time, I'll do 90-95% . I've got everything to lose red lining it for too long.

Why's that? 2 strokes run best at full rpm I thought? Think of a chainsaw. I guess you're not using a chainsaw at wot for 30 mins straight though. So good point there!

I'll agree that 2 strokes work best at high rpm's, but I don't know about full. All the two stroke yard tool tuning guides I've ever seen, say to adjust the high speed circuit to max max, then back her down a little bit. Favoring the rich side essentially. Then it's just short bursts while you work and then down to idle again.

To the OP,

I was reading your post and I was digging all the data that you posted. I can assure you that the RPMs on the PX150 are not as high as you think. I have done plenty of trials on my PX150. I measured the speed when it was stock, with the Malossi 166 and even when I slapped a P200(Malossi 210 cc ) engine in it.

I maxed out 58mph (speedometer) on my PX 150 with a Sito plus and that was exactly 50 mph on the spot. I run a tachometer now and I measured the speed and rpms at max. for instance I see 65-66 mph (GPS) at 7500 rpms. I can dig in more into scooter help website and pull the gear ratios.

On an almost stockish PX150 you might perceive the speed as if you are flying but you aren't. If I have to throw a wild guess I would say you are probably just below 6000 rpms but it might appear that you are flying. If you can do a GPS read out we can probably pinpoint the speed much better.

And when i said the top speed on my Sito+'d PX150 was about 55mph, the actual top speed on a flat road in optimal condition is 57mph.

*my buddy and i were on a loooong road trip, me on my P200, him on a 2005 PX150 with a Sito+. Anyhow we were coming about a really steep mountain pass that was about 5 miles long. He had enough camping crap stuck to his scooter, plus he himself did weigh a lot as well...but he got that scooter up to 71mph! This was verified by his GPS, along with my GPS as well. I rode right next to him while looking at his GPS and mine at the same time. I was pretty amazed at his speed.

^^ WOW!!

I once did a 200 mile round trip from Toronto to Midland Ontario on my bone stock P150, mostly at full throttle. I think the fastest is went was 50-55 mph. Gutless on hills. I warmed up a couple pieces of cold pizza wrapped in tin foil stuffed under my engine cowl. I'm lucky I didn't overheat. Engine cooking was a thing in the late 80's. Not a great idea for an air cooled Vespa.

Not sure your maxing out on revs, my experience is that, you think you are maxing out on the road but if you pull the clutch the engine has far more revs to go at.

On a 2005 PX150 even 71mph down said massive hill, is still only 7500rpm. Under the theoretical max fat piston ring rpm.
So anyone with a stock 150, thrash it as much as you like.

So I went back and took a look at the PX 150 late model EFL and at 6000 rpms you are doing 57 mph. I don't know many people on a stock PX150 that would do 57 mph(GPS). My 05 PX150 did 58 mph(speedometer) tucked down with a sito plus and that was 50 mph.

If you are doing 7000 rpms you would be traveling at 66 MPH(real GPS) which means your speedometer would be reading like 75 mph. If you are doing 7500 rpms you will be adding another 4.5 mph(now you are at 80 mph speedometer) and 71 mph real speed GPS.

Again, it is very hard to believe that a PX150 would do such speeds stock specially the US version with a catalytic converter and a restrictive 1" pipe loop that they come with.

I struggle to hit 7500 rpms with a Malossi 166cc and a 177 cc on a flat road tucked down(I have a tachometer).

Here is the gearing calculator. I am tempted to put my stock cylinder back and see what it does again. I only managed 50 mph(gps) on a cold night tucked in with a sito plus.
https://www.scooterhelp.com/cgi-bin/vespa.gear.calc.pl

Before i reply to your post, can you do me a favor and go back and edit out all the mph speeds that you were reading off of your speedo? We all know just how inaccurate the vespa speedos are...at least all of us vintage crowd knows it. One of my 05 Px150 speedos reads about 85mph @ a verified 60mph gps. Posting up whatever the speedo shows just confuses the heck out of me, just because it's throwing too many #'s at me at the same time. It doesn't help that i suck at math.

Or maybe my stock speedometer is just pain faster than yours!

^^ ... Fair enough my friend. I agree with you. The speedometer reading are truly inaccurate and a bad reference. My P200E reads 10mph+ less while the PX 150 read 10mph+ more. We should stick to GPS reading.

Fortunately I do read my speed on at least 1 or more GPS devices and I use a Tachometer as well which helps a lot.

I own a US 2005 PX150 that came with a cat exhaust and strangled jetting (EURO2 spec I think ) and pardon my ignorance, but what is a "pipe loop"?

I think stock engines are deliberately detuned so as not to blow up at full throttle. I'm sure it was a consideration when the engine was designed; anticipating that some would ride it full throttle all day long. All the power is in before blow-up revs can be reached. The power curve, if unexciting, is smooth and predictable. Shifting is easier and more forgiving on a stock bike. 3rd gear in the 200 goes on forever.

So I am here to give you guys an update and to correct myself for any confusion or misunderstanding. A few days ago(20 January) I wrote a reply. Apparently either I wasn't using the proper gear calculator or I don't know if my PX150 (2005) comes with what it suppose to come.

Long history short, last Sunday I was very bored and I removed the existing Malossi 166cc and put back the original PX cylinder kit. I do have a trailhead digital tachometer and a GPS so I went to see what top speed I could achieve. I read 7170 rpms in 4th gear and I was tucked down. My GPS showed 58 mph.

My mods are a 26mm Carb (Spaco) a P200E air filter with crossed drilled heart and a Malossi box and a 103 main jet. That is a solid 8mph increase over my original 50mph on the same Cylinder with the original 20/20 Del'orto and a Sito plus. Back then(11 years ago) I did not have a tachometer.

I have been in contact with a buddy of mine on this forum(MJRally) and we were trying to figure out the exact gearing that my PX150 comes with. It was built in Sep 2005. For now, all I can say is that I reached 7170 rpm on my tachometer and I saw 58 mph on my GPS. My Malossi 166 was reaching 7500-7600 rpm and I was seeing 65-66 mph on the GPS.

If someone can do the math and use the scooter help calculator I would appreciate it. I tried punching the numbers and I am slightly off with the mph/rpms. I can't guest what gearing I have.

This is another update newer than the one above. I just rode with my son into a deserted road. We were doing roll acceleration on two scooters but I decided to just leave the PX150 in third and see what I would get. I saw 7600 rpms on the stock cylinder and the speedometer was a hair over 55 mph but I know is not accurate. The cylinder engine is a pig, it took a while to get the 7600 rpms in third, it had not top end. This answers my own rev limit question because like I said earlier, it has been 11 years since I rode this stock cylinder and I did not have a tach back then, now I do and I saw the other day 7170 rpm in 4th tucked down and this afternoon I saw 7600 rpms so there you have it, that is my contribution. By the way, I am looking for a new modern cylinder kit again.

Find a REAL steep, REAL long mountain highway (preferably over 4 miles long and a 6%+ grade). I betcha you can get the PX up to a GPS verified 70mph! Because that's what it took for my buddy to get to 71mph on his stock carb and cylinder. It also helped that he weighed about 230lbs...plus another 60+lbs of camping gear that was lashed to the poor scooter. But on the flip side he was struggling to maintain 45mph on a flat road with a tailwind.

I actually have a 3-4 mile stretch of road downhill with a step angle(6% or more) nearby. I did the math and if I was going 58mph at 7170 rpms you would have to travel at 8747 rpms to achieve 71 mph on my scooter(Holly crap!!). My gearing is a stock PX150 built in Sep 2005.

I'm looking at the hearing calculator at scooterhelp, and i'm coming up with closer to 7.5k rpm

Calculators don't take into account wind resistance

Went back again on the PX150 (stock cylinder) now with a SIP SR3. I read as hair over 7200 rpms on 4th gear tucked down, saw 58 mph on the GPS(same as with the Malossi). I just told username MJRally that I am going to start a YouTube channel this week.

The reason why I want to start a YouTube channel dedicated to vespas is because I am true nerd when it comes down to statistics and testing data. Like I said in the past, some days I am so bored that I will go and switch a few exhaust (4-5) back to back just to test them or because I am bored. I just switched cylinders because I felt that I was very bored and I wanted to wrench. Besides that I just have instruments and measuring devices and I love to document everything.

Time for me to share. I also have a ton of free time on my hands and I love doing it as a hobby.

wind resistance will change your top speed because you have to overcome it, but it won't affect the relationship of MPH to engine speed based on gearing.

I am back at it. I tested the stock exhaust. I got 6800 rpm on the stock PX150 engine and a 26/26. Reached 55 mph on the GPS. It took literally 400-600 yards to go from 54mph to 55mph tucked down.

1)pass 0-50 mph 22.62 sec but to 55 mph in 38.61 sec(dragy verified)
2)pass 0-50 mph 24.86 sec but to 55 mph in 39.65 sec (dragy verified)

Eat more pies and find a much steeper mountain to ride down! Though i would never believe it if someone ever told me, but my buddy did get his stock 2005 PX150 with a Sito+ up to 71mph. The total weight of my buddy with all his riding and camping gear probably totaled to around 325~350 lbs. Yeah, he probably had about 100 extra pounds of crap strapped on his scooter. The mountain highway was REALLY long (multiple miles long) and REALLY steep. I was on my stock P200 with a Sito+, and it took me a few minutes of WOT to VERY slowly overtake him. We both had Garmen GPS mounted on our individual scooters. His GPS read 71mph and mine read 73mph. On the flat road with no headwind the Px150 did struggle to maintain 45mph.