Modern Vespa

Hello!
I've decided to stop busting @Jim van Morrisey's and taking this discussion to a wider audience than our chat. Thanks for the help so far Sean!

I have a PX200e since a couple of years ago and I've been restoring it stock. It is important to mention I live in Quito, Ecuador (2,800m above sea level). This is my 3rd Vespa. I'll share some photos of the other ones later. (PX150e & VBC)

I installed a 2nd or 3rd OS Meteor piston (Scooter Center) to address 'lack of compression' from the previous one. At first I didn't realize the bike had a 94 main jet and one of the idle jets with the solid top. The bike had a very hard time going uphill, and it seemed to soft seize/stall in urban uphills.

I chatted with @jimvanmorrisey and followed his advice to install a 160/55 idle and a 110 main. (160/BE3/110~).

~. However, the local mechanic had to fit a small copper filament from a wire to make it somewhat smaller, as it was bogging BIG TIME and with flooding symptoms all over the place without it. It is not easy to find jets here so that is the local fix to make them smaller. Still larger than the previous 94. The bike is much more awake and powerful in flat rides and does small urban uphills in 3rd just fine. I was confident enough to try a longer ride today (1 hour, 300m altitude change) and things were fine flat and downhill. I checked the spark plug and saw the chocolate color for the first time (photo below) so I decided to keep going.

I had a couple of soft seizes that I controlled with a fast clutch action when going almost WOT or WOT in 3rd for a small period. 4th gear seems not as powerful but I think this may be because im still running in the new piston.

After a 30 minute stop at the lowest point of the ride, in the city suburbs, we took a faster road uphill and the bike seemed to struggle in 3rd and 4th gear,
or not be as powerful. As if it doesn't 'develop', we say here. Running in period?

The big issue came again when heading uphill towards the city. The bike stalled/soft seized at least 4 times and I was getting anxious. Clutch saved me every time! I saw the spark plug half way uphill and it seemed whiter than before, but not too much. still pretty chocolate. However, it was VERY HOT to the touch. I opened the mixture screw half a turn out of instinct, and managed to get the bike back up into the city after at least a couple more stalls/soft-what-nots.

Please share your thoughts! I've spent hours reading Aviator's posts and others I don't remember the names now but I've finally decided to ask for specific help!!! I'll be splitting that top end this week to see how is that piston doing. Probably check the rotary valve with a feeler too.

PS, let me invite you to the Vespa Southamerican Days in Quito on Nov. 25-27 2022. Let's ride along the half of the world or Mitad del Mundo!

P200's run a 112-116 main, so your main jet is too small. For steep roads you will probably be in 3rd most of the time.

Thanks orwell84!
The thing is it was bogging at 110. I was doing fine in hills at 3rd with the copper wire inside it, so I think it might be equivalent to a 102 or so. I also have a 114 jet. I'll try that one with the copper wire to see what happens, until I'm able to buy 102-108 jets. Altitude is 2800m, hence bogging with 110 main. I'm sure it will bog more with 114 main w/o the wire. Either that or I got a faulty 110 main.

However, when I need to ride 2nd, and there are hills here that require it, that's when anxiety begins!

He's at altitude, the expectation is different.

Did you gently break in the new piston? Low throttle/ easy shifting for 200 miles?

I've gone by the rule of drop 1 main jet point for every 1000 feet of elevation. So, stock 200 cylinder with no modifications, stock air filter and stock exhaust has a 116 MJ from
Piaggio. At 2300m that would take you down 8 points to a 108 MJ. You will have to adjust your idle as well for altitude.

If you have any carb modifications, air filter or a performance exhaust you need to add points to your main jet before you can take away 8 for elevation. Do you have a bell mouth on the carb? Air filter drilled? Non stock exhaust you haven't mentioned?

Until you clean the cylinder and replace the piston, you will keep seizing. Be very careful riding this until you have a new piston installed

I think I'm repeating myself over and over again in different threads, but here goes: have you done a pressure test on the engine?

That's good drum banging…

Eventually people will understand.

When soft seizing, it's not a little bit lean, it's extremely lean. Something is really wrong.

Took the words out of my mouth, Yes, no point guessing jet configs unless this has been done.

Yes, already at a high altitude and climbing 300m. Mount Washington in NH is only 1,290 m so you are right.

Thanks to all for your replies! I popped in a 114 (+ Cu wire - see photo) jet this morning and it was very boggy around the block. I then popped a 112 + Cu wire MJ and the bogging was gone for the ride around the block. The moment of truth will come when I try this setup uphill next week.

MJRally, I'm currently on that running in period. I haven't been able to ride without the soft seizes or the bike drowning/flooding when I had the 110 MJ + no copper wire, or even before, with the blocked-on-top idle jet. I've probably done 40 miles since the piston change. Probably, there's been 10 stall/soft seize events in that period. I'll take out the cylinder head to check for damages. How to know if this new piston and cylinder heads are still in good shape?

The only mod I have done is the drilled air filter, ~5mm and 7mm separate holes. The exhaust pipe is stock. This is a new piston. Do you mean I need to replace the piston again?

Could it be an air leak? A faulty rotary valve? I don't know where to look for the damage and it has kept me from being able to use the bike. Very frustrating if it weren't for you guys, and Jim van Morrisey, haha.

FINYoshi, thanks! I'll look up for your previous posts on pressure testing the engine as I haven't heard of this before. Is it the same as compression tests for the piston?

I'll

I'm mainly @2,800m = 9,200 ft. Following your rule, and since my bike is autolube, I'd say 107 is what I need.

Maybe I'm getting close to that with the copper wire on the 112, until I can get my hands on smaller jets (105-109)

Hey alejo, it's different. You're essentially pressurizing the piston, cylinder, and gears area to see if any seals or gaskets are leaking.

About 5 PSI in the engine case should be enough to see if it leaks. This is done in a variety of ways. Lots of homemade setups. Plugging off the bung, rubber under the carb, and adding pressure through the spark plug hole is one of the ways I do it, with a blood pressure cuff gauge, so I don't put in too much pressure, and it's easy to see a leak.

I've had a leak three out of five times that I've put an engine together. At the base of the cylinder, the carb, and a brand new seal leaked.
"
If you do a google search for "leak down test vespa p200" you'll come up with lots of variations.

Good luck and let us know how it goes!

EDIT: I'll take a picture of my setup later and post it here

Ok, took a picture of the new setup I use.

Air goes into spark plug hole.
Rubber under carb to seal it off.
Rubber cap and clamp to seal off exhaust Port. You need to remove exhaust.

The old setup was using the inner tube clamped to the exhaust. Leave the spark plug in, and same rubber bit under the carb to seal the inlet. The inner tube would slightly swell with time so it would show a slight leak, when it wasn't. The new way Is more accurate.

Doing this test each and every time I pulled the head or cylinder has saved me many hours trying to chase down jetting issues...

Hope this helps.

Here is a good article on high altitude jetting. I have also heard a "rule of thumb" that says drop a jet size for every 2,000 feet in altitude.

https://www.horizonsunlimited.com/hubb/suzuki-tech/high-altitude-carb-jetting-8431

So, at 2,800 meters there is only 72% of the air at sea level. Does it follow that you would then need 72% of the fuel (jet area)?

114 MJ=1.021 mm2
97 MJ=0.739 mm2 (~72.4%)

Someone check my math.

I posted it here a few years ago. I live in Tucson but we have mountains here in the city and a ski station. I made it to the summit (9200ft at Mount Lemmon) at least half a dozen times with at least 5 scooters ranging from GTS 300ie, P200E with malossi 210, PX with a 166, Stella 4T, Lambretta 125li (stock) and again with a PX150 166cc with a passenger.

I found out that on the 5500-6000 ft most of the scooters would fall on their face. I never adjusted the main jets though. On my experience just going up in an incline and picking up altitude will kill the power. There is so much that you can do but there is a lot that is out of your hand. You could technically stop one or twice and try to re-jet but in my opinion is not going to make a lot of difference. Simply put , we just don't have a lot of torque on these scooters to overcome the altitude.

As far is your main jet, what you are running is too low. The P200 takes 116 and up. on a side note, what I think would help is picking the correct exhaust. There are some exhaust that will give you a better torque/power band in the mid range for climbing. I have done some climbs where I had to shift to second and keep the rpms high because it would fall in its face on 3rd.

I also forgot to mention. What oil are you using? A long time ago I use to have soft seizes, everything stopped the moment I switched to Motul 710, never again I had a soft seize, I know Motul 710 is expensive but is a hassle free.

I'll open the top end tomorrow to have a look at the cylinder and rings, maybe look for oil sucker signs inside the crankshaft, and upload some photos.

My question is, can an air leak only affect things at high revs? At low power and idling, everything seems fine.

This doesn't seem at all crazy, since the bike originally had a 94 MJ!

Your starting point may be 116 (1.057mm2) for the 200 autolube. My math estimates a 99 MJ.

I was able to ride a 110 with no bogging problems in 3/4 throttle and above, but it still stalls on 1st and 2nd gear on a longish climb and at WOT in the highway at 3rd and 4th. Am I soft-seizing or is there another type of stalling?

An air leak makes the fuel mixture leaner. It may even feel like the bike is running better and goes faster. Then when you roll of the throttle it can seize because it suddenly gets a lot less fuel (and oil).

I opened the case and the cylinder today. There weren't any signs of deformation in the cylinder. The piston has these marks but they aren't sensible to the touch. There was a gas scent in the gearbox oil so we'll be replacing seals crank side and clutch side too. The gasket between cases is also gone, but didn't show evident leaks on the thinnest part, however that gasket will also be new.

How do you guys see the piston?

It should be ok. Show some better pictures when it's completely off. It was running very lean. Top of the piston should be generally black with a wash pattern when running well.
Pressure test the crankcase before putting the clutch on.

Hello all! I'm sure many people in this forum has lived a similar day than today. We took the engine down, opened the casings and discovered the price of time and its many wonders

A compression tester is $60+ over here without the mods or even gauges with the proper psi levels for the air leak test. I'm gonna have to trust my mechanic who has previously restored a PX150E and I've ridden it (with a 94MJ!!!) for years without trouble or hesitation.

I'll write a follow or edit as I remember the details. The gas smell in the gearbox was the indicator to take it down and open it up.

FWIW, and from what I can recall right now, the following work has been done. I couldn't take more pictures unfortunately.

- Rotary valve rebuilt
A common practice here seems to be adding material to the crankshaft somehow. Fortunately in my case they added to the casing.

- New oil seals
- New case gaskets
- Several holes in the case that were previously soldiered have been re-soldiered with a special type of soldiering. This was done near the kickstart shaft, and somewhere inside the clutch side of the casing, and somewhere else I'll have to ask again. There's a big bolt with a special type of square locking washer that splits.

- The hole in the casing where that bolt was is apparently bent. An oil leak will indicate another place to be fixed, in this case with cold weld (JBWeld or similar).

- No manual sanding on the piston, cylinder or rings, as they showed no damage signs, and I was skeptical of manual re-boring.

- Kickstart stop rubbers replaced
- 2nd gear piston replaced
- Stator rebuilt replacing 2-3 damaged coils from an old coil

I'll pick it up and drive some blocks to my house and let you know how it goes.

Overwhelming day at the mechanic shop!

The lighting was very bad that day at Quito's Vespa Servizio! The piston had an even thin black layer. Those spots were done by my fingers at a very gentle touch.

Hey Alejo -- Seeing as you had gas in the gearbox oil, and Quito's Vespa whisperers went to great pains to weld up what sounds like a crack at the input shaft's hole by the clutch cover (which is common), and replace all the seals -- well, it's all but certain that you had an oilsucking situation and the air leak to go with it.

That would explain the gooey black piston head (gearbox oil is filthy, doesn't belong in the combustion chamber) combined with a tendency to seize. In short, all of your jetting adventures were an attempt to 'jet around' all this false air getting in there, and were ultimately fruitless. Trying to dial in a leaky engine frickin' sucks.

Assuming you've got a buttoned up engine now -- it's a shame you can't pressure test it -- and assuming they did a good job repairing the rotary pad to 0.05 - 0.10mm clearance, you can start over with getting the jetting right. Based on my experience with Quito's elevation, you really should be landing at 108-110 for the main jet. Just don't do what I did and forget to upjet to 116 the next time you head down to the coast!

BTW is that oddly Canadian-themed burger joint still running?

Thanks Sean! The King's Cross is still going strong and is *probably older than this PX* haha.
Good times, about 10 years ago. You should plan a South American encore, as there are many breweries and local spirit distilleries around here now!

What you describe sounds about right, plus the other welding spots. I-ll tell my whisperer Marcelo to try and get rid of the copper wires this afternoon. I should've taken you there instead of going to Patio de Motos.

I expected the piston and cylinder to look way worse given all the soft seizes you described. Worse than finding a problem like an air leak is not finding a problem and dealing with an endless mystery. Glad you are getting it buttoned up.

I picked up the bike, and it's running so much better! Everything feels colder, smoother than before, and maybe what I thought were soft seizes were only fuel starvation stalls. Fingers crossed.

Now it feels like a bike ready to complete the running in period, kind of becoming more pleasant to ride with each km. Throttle had kind of a slow response off idle, and I screwed in the air screw a bit, maybe half a turn. It felt too much as the fork was trembling when I released throttle. I unscrewed 1/4 and that feels good. I'll check the spark plug as soon as I can.

I'm now running a 112 MJ with a .05mm copper wire mod, for a total of say… 107 MJ.

There's lots of blue smoke when I rev it hard, but I'm guessing the flat pancake beat up stock exhaust is the one to blame. Could that make sense?

I'll be testing the PX on the long steepish climb from Cumbayá (the suburbs) these days.

How do you see the spark plug? The air screw is at 1.25-1.15 turns out. I finally made it up the hill! Smile in my face despite our national team's loss in Qatar. Anyone a fútbol fan around here?

55/160
160/BE3/~107(112+0.05mm Cu wire)

Do a search for plug chop, it's really hard to tell what you have as what we see is what was occurring last. Color would be at idle.

As I'm adjusting the air screw isn't idle what I'm trying to set correctly? I'm not thrashing it as I'm still running in the new piston and rings (3rd OS)

I believe this is spot on! I tried the 110 w/o any wire and it bogged a bit. The 112 + wire is a 107 I estimate. I'll buy a 108 whenever I can, or maybe not, as I'm looking for a Polinibox 200 in the USA. Know if any dealer? Until that, it feels great to ride. Thanks man!

EDIT: holes above the air filter, not the entire heart, and still 107ish

Café con leche!

Rides great at 1.20 turns with a 55/160, and 160 BE3 107. Thanks for the 1000 ft. rule. That will be the norm for me. 9 steps less @2,800m.

The SIP road 3 arrives next week!! I'll test 114-110 Jets.