Modern Vespa

The centerstand springs are covered in Polini's instructions. Just remove the clips from the crossmember and hook the springs directly into the holes where the clips used to go. Worked fine for me.

Hi Guys
Firstly thank you for all your input,veryy much appreciated. Finally solved the problem, it turned out to be a very slightly damaged thread at the tip of the bolt which engaged when dry fitting off the scoot but on the scoot with a fractional mismatch refused to thread. New bolt solved the problem.
Next question Jet stack on my px is the standard 140/BE5/96 main. Ive changed the jet to a 106 ( 112 and 110 just flooded the engine) and seem to have it running ok to my ear (but I doo wear hearing aids so not sure how good that is) Is there any procedure/guide That is fool proof or does it come with experience?

Cheers Andy

Last edited by andyx on Fri Jun 24, 2022 8:30 am; edited 1 time in total

What exhaust are you replacing? Jets on a SI are so easy to replace I'd start with that 112, make sure it's running rich. Should be to big, guessing you won't get around block as soon as you open throttle past 1/2 it'll just bog down rich. Leave motor cowl off, pull over replace jet with a smaller one and try again. Depending on sizes you have start working your way down by a size or two. I know you can get singles 112,111,110 etc in that small size, not sure what you have. It's only n time and a good learning experience.

Thanks Chris as you rightly surmise 112 was way too rich. I'm at 106 now and it seems to be running wellBut not keen on a lock up, any foolproof way to be sure I've got the right jetting or is it a case of feeling my way aroound to a degree.

Nothing is fool proof , I'm a technician by trade, to measure is to know, is my philosophy.

1) CHT - cylinder head temperature - it does work especially for longer sustained runs, not as fast as EGT. Cylinder head mass has a larger mass and slower thermal change. That has left me with a seized cylinder previously. Gauge was still climbing past 350°F as cylinder locked up. I like it better for a stable or sustained reading.

2) EGT - exhaust gas temperature - quicker reaction then CHT as it's measuring exhaust gas and only has to change thermocouple mass in exhaust.

3) Wideband AFR - air fuel ratio - quicker then my EGT - it's a love hate relationship for some. I have been jetted so lean it just showed said lean and I stopped and turned it off immediately. Cylinder head and EGT hadn't had a chance to read anything.

4) Plug chops and cutting plugs open, can be a pain the rear but do work.

Thanks Chris, got a cht probe, which I'll fit when I replace the rear shock (next job).
Just want to avoid a seize and chucking my 66 yearold body down the road

Yeah, wouldn't be any fun at 49 either.

How did you arrive at 106? If you go up one jet size how does it run? I think you said your missing a 108? Ok I see you edited previous post, you went from a 110 to a 106. Theoretically you should be ok, temperature readings would be best, maybe try a 108 if you can get one, best you can do is run on rich side for safety.

I've got a 108 so I'll try that over the weekend but what will tell me if a jet is too rich?

Without indicators such as EGT and CHT, as long as you can still rev out to max rpm, cooler you will run. As you get leaner you can still rev to maximum rpm but you'll be hotter, to hot everything expands, to hot aluminum melts.To hot, oil reaches it flash point and no longer lubricates cylinder walls.

How on earth are you considering that jet size? That's way too high. A road 2.0 sip will be no more than 102 on your jet stack and that's with derestricted air filter too. The polini isn't as powerful top speed as a road 2.0, it's a good 5 mph slower and does not rev on like a road 2.,Without seeming to be arsey we are repeating the info you ask for when it's already been given . Anything like a 108 will rich bog like hell, your plug will be black and wet. It's a standard 125 we are talking here with a rather mediocre box pipe on a standard cylinder . 101 or 102 jet !!! You are going 12 pts over standard jet with a 108, even your polini instructions will state 4 pts over standard !

Hi ferriswolf, thank you for your input but the 106 isnt bogging (had to google that) with the polini and the drilled filter and I'm real new to this and want to avoid seizing the motor and me sliding down the road on my arse.
I'll try the 108 and if it bogs I will have an idea where I am.
Until I get the cht fitted I will err on the side of rich.
Will let you know where I end up

I agree with ferriswolf. If your only mods are a Polini box and a drilled airfilter, your main jet should end up in the 100-102 range.

When you are dialing in a main jet, you are looking for splutter (better descriptor than "bog" in this context I think) at max rpm, i.e., wide open throttle in 3rd gear. It took me a while to learn the difference between a motor that was spluttering and a motor that was revving all the way out, and it is hard to put into words. Of course there is the actual splutter. Beyond that, the best way I can describe it is splutter will feel like the motor is hitting a wall, revving out will feel more like the motor has reached the end of its tether.

Yes it's a gurgle sound , not smooth . Like hearing somebody gargling . You should gauge the plug colour and not going higher on the jets till you splutter or lose speed as not enough air and too much fuel. By all means go to a 104 but you will still be Rich. Then work down.

Thanks guys for your advice and your patience, next step I think is to fit the cht as a back up while I learn to work out what the engine is telling me.
As
before I will keep you updated with my progress on this learning curve.

You have px 125 2003 , I have px 125 2003, it will be an MY disc model .
When I had it standard other than a sip road 2.0 and a derestricted air filter it's jetting was 101 and perfect. It's as simple as replacing your main jet and sticking on your air filter. This is a five minute job. Then you whack your exhaust on, about a 45 minute job. You really don't need a temperature reader. Your scooter will do the same top speed as it did before however with the polini box it will be more eager and torquey in third and from third to forth where it will reach its maximum hp as it can't rev on . If you had a road 2.0 pipe , jet would be 101/102 depending on climate , season as it does have a better top end over standard . I've run both pipes matey preferring the road 2 . I now have a dr177 bolt on and this is where the experiments with jetting , air correctors and atomisers come into play and where a temperature meter could be useful however I have learned with help on this forum how to plug read across all running speeds and the folk on here gave me the likely base jetting info for my kit as they have either got that kit or used to. So yes learn at your own pace but accept the giveaway information to start you off with and keeps it simple and cost effective .

Thank you, I am taking your advice, tomorrow I will be removing the tank to replace the rear shock, while I'm at it I will fit the cht gauge and replace the throttle cable and start coming down with the jets. For me it will be interesting to see the correllation between temps and jet size and performance. Even with the wrong jet in the engine has a lot more botom end and I hope/expect it will improve as I get close to the optimum setting.
It seems to me from all the reading I have done on this forum that developing a 'feel' for the engine is invaluable and thats what I'm trying to to in my cackhanded way.
Please dont take offense if I seem to be a little slow following your advice I am just tring to do it in a measured way that makes sense to me.
Please stick with me as I know your advice/help it the future will help me when I fit a kit, which will be neccessary if I am ever to make the sidecar outfit viable.
I see we live in the same county, maybe we could meet up for a chinwag( coffee's are on me)

You fancy one of these ?
https://beedspeed.com/products/vespa-cozy-side-car-zeppelin-black

Nice, but they also do a 'rocket' shaped one which I'm tending to favour.

A question that has just occurred, My engine was rebuilt 600miles ago(rebored cylinder etc.)
Should I still be running it in and if so whats the best way?

600 miles is plenty for running in.

Thanks for that

Ferriswolf
Think I have found an issue which is possibly affecting the jetting?
Removed the carb and found the gasket was mis fitted, cutting off 20% of the intake.
Any thoughts as to how it would affect the fueling?

Hi All back after work interupted my progress/ experiments/learning curve.
Anyway I have fitted a Runleader Temperature gauge and worke my way down to a 102 jet.
I was a bit apprehensive as the 106 jet gave me temperatures of 320 f.
Anyway just been out for a run and would appreciate your thoughts on the following.
With the 102 jet i have max temps of 245 the bike will max out rev wise at 7500 in second and 7300 in third( although given a longer run I think I'd eventually get to 7500, just run out of road). To my ear the engine ( bearing in mind my hearing is impaired) sounds good, picks up well, returns to tickover straight away and with the polini the torque is much improved. I think Im at the sweet spot as Ferriswolf correctly surmised, bearing in mind I'm after a reliable runner.
One other question, what should the tickover be? set at 1200 the scoot occasionally cuts out, at 1500 its fine(have I answered my own question?).

Depends on your flywheel setup…

Stock flywheel is around 900rpm,

Lightened aftermarket (around 1600grams) should be 1100-1200rpm

1500rpm will be too high… you'll be crunching the cruciform to get into gear from idle. It'll take an unwanted beating. You want to aim low…

Usually if it won't idle properly at the right rpm, it's the fuel/air mix screw + pilot jet + idle screw not set properly

And the mix screw is a right pain in the arse on your model as you have an electric starter motor in the way, i hate adjusting them. If you havent ever touched your mix screw its likely in the right spot from factory although they can get crapped up inside. Why not just adjust the throttle slide screw and take the revs down and see if it cuts out. If it cuts out then yes, you gonna have to get to the mix screw and adjust. On an SHBC carb its dead easy to adjust, SI carb on the MY 2003 125 model royal pain in the arse. What fuel you running , e5 or e10 because the running conditions i have found in tickover is impacted by the differences in these fuels. When im running the PK i slightly adjust mix screw depending on the fuel put in , this is down to availability as not all petrol stations sell e5. Once you get yours right, stick to the same grade fuel if you can.

Thanks for that 108, I believe the flywheel to be standard solooks like I need to do a little tweaking.
Another step on my learning curve.

No worries!

I asked the guys here too, asked others, researched else where, used my own experience of trying numerous hours of dialling in and using several rpm devices. Lol

But it has worked out well on those numbers.

From experience, your mix screw (if untouched…) will be set for stock setup, if you've added a kit, most likely you'll have to set it leaner or richer to get the optimum running at idle to match your idle jet.

The only chance you wouldn't need to do that is if the bore, stroke and ignition timing is unchanged.

If you want to refine the tick over head to this link

Mixture screw adjustment, got a good link?

Thanks Ferriswolf I'll have a look, time to get the hands greasy.

Thanks for that link Ferris wolf, About a quarter turn has sorted the problem, But what a pain in the a..e to adjust. Its a shame the designers dont have to work on there own designs.

Yes, dreadful . It's the starter motor . Best off without them and just use the kicker . Remember what fuel you have in it now as the e5 and e10 change that tick over characteristic. You might find that waiting at traffic lights your engine will stop as ticker over too low. Can't remember which way but one will make tick over lower, I stick to e5 where I can get it.

Not sure whats in it at the moment ( I bought it with a full tank) but intend to run it on e5, dont trust that e10 stuff ,it affects my cars.
Must say that the polini exhaust has transformed the bike, much more rideable, rev limit is about 7500 with it, but thats fine for me and it becoming a sidcar outfit.

Yes they are great for around town , the punch in third gear is good and the change from third to fourth retains speed and doesn't drop the revs down so much. They sound the nearest to original . The road 2 will go faster top end but are noisy , after a couple of years they get loud. You made wise choice for your intentions. One thing I'd say to use as your scoot is same age as mine, if the fuel line not been changed please change it. It will be very brittle and will rupture on to your exhaust . Can guide you on that how to fit as there is a certain art to it.

Thanks Ferriswolf, The scoot was rebuilt by retrospective scooters 600 miles ago and when I hade the tank out to replace the rear shock the fuel pipe looked nice and new and was flexible.
You're right about putting the fuel pipe back it is a bit of a faf to say the least but another skill learned.
Nest stage is to tune the 125 cylinder to see what I can get out of it. ( more as a learning thing ) then decide what cylinder kit would be best for pulling a sidecar.
Going to follow this guide.

https://www.scootering.com/scootering-classics-vespa-tuning-upgrade-mega-feature-part-3/

Must admit I'd forgotten what fun vespas are, to ride and work on.

Have you thought about just sticking a 150 barrel on it? If you're not looking to go kits , imo the 150 was the best capacity ever made for the px. Better fuel consumption, a little bit more power, not much difference in top end that can't simply be done with an exhaust change but a bit more torque. I've had a couple of 150 px over the years and they were good all round. Theres the LML 150 barrel piston and head kits still appearing online and they have the couple of boost ports in too. Used in the late LML star models in the uk. Called a stella in the USA I think .

That thought had crossed my mind Ferriswolf ,but the question is would I get enough power from that to pull a sidecar in any meaningfull way?
Im not aftera rocket ship but on the other hand dont want to be overtaken by mobility scooters either
The tuning of the 125 barrel is just to get my hand in ,so to speak, its not intended to pull the sidecar, more to get a feel for mucking about with tuning a 2 stroke.
When i do kit it I want to have half an idea about whats going on and especialy the jetting side of things as that sems to be the key to a reliable engine.

Ok in the spirit of learning something( and I am an inveterate fiddler) and having a day off, I whipped the head off and sanded 1.5mm off it, Then I raised the cylinder .8mm( its all I had)
Bolted it all up and went for a ride.
Result? A definite improvement in driveability, not a massive change but it is easier to ride.
Worth all that sanding!

That's the spirit!

Learnt some things along the way, e.g rings were fiddly to get back in the barrel, couple of nylon zip ties( cable ties) and it was a doddle.