Modern Vespa

Greetings all

Here is the scenario. I have a 2003 ET2 where it started to die on me. It never dies when I'm scooting around the neighborhood where there's a lot of start / stops going on. It will only die on the straight runs where I go around 35-40mph.

What do I mean "it dies"? Well, it will act like I flipped the kill switch. Sometimes I can tell when it's about to happen where I can hear and feel the engine starting to cut out and then it's done and it coasts to a stop along the side of the road. Starter turns over fine and strong. It never fires again unless some time has passed.

Here is where it starts to get weird. I've brought a spare spark plug along afterwards. When it dies, I pull the plug cap, plug in the spare, check for spark, yup there's spark, and then when I plug the cap back onto the ET2 plug, it starts up! I can do this every time it dies. It also doesn't seem to matter if I drive it around the block several times where the engine gets nice and warm, then take it on the straight away or if I go straight from my garage cold and do the straight away right away. It will always die in the higher speeds. Pull the plug cap, check for spark, plug it back in, I'm then able to drive back home.

This felt like an electrical issue. Here is what I've replace and nothing I've done seemed to make a difference.

Replaced the spark plug
Replaced the spark plug cap
Replaced the CDI
Replaced the Stator

I've also disconnected the CDI lead that goes up to the ignition switch to bypass possible switch issues. It runs just fine without that plugged in, but the symptom is still the same.

Now for some more details about my ET2
I'm the original owner. It now has close to 25,000 miles. I have never replaced the rings or done a top end job on it. When I test the compression, it's @ 90psi cold. I understand this is low and also unusual for this model to go this long without this type of work done. I will order the needed kit to address the low compression. However, what I described above, would the low compression result in what I'm experiencing? If it wasn't for the whole spark plug test I do to get it to work again, I can understand that being the case.

Thanks for your thoughts….

Sounds like a fuel starvation issue. Pinched fuel line or something slowing down the fuel flow.

Wouldn't that be more of a stutter than the sudden death described?

It could be a heat-sensitive coil - I've had that before. My local dealer in the UK made up a test rig for coils - as some can take ages before they show symptoms. Without that the only way to test is by substitution. I'd be replacing the HT lead as well - though by the sound of it that's probably OK.

I've seen both! At speed, just a straight up die. At lower speeds, the stutter that reminds you to switch to reserve

Fuel Starvation
Not ruling that out and will double check the lines. Would the whole spark plug test I do make it run again if it was starving fuel? When I don't do that, I can crank it for a long time fluttering the throttle now and then, won't fire up.

Heat-Sensitive Coil
Not sure if I understand what coil you are referencing. The windings in the stator.

HT Lead
I had to search this term. High Tension Lead? Is that the cable from the CDI to the spark plug? If so, when I replaced the spark plug cap, the cable was part of the cap as well.

The fuel tap is vacuum operated. When you crank the motor/normal running, a vacuum line opens the fuel tap and fuel can flow. When the motor dies, a spring closes everything for emissions.

The cranking after parked helps re-prime the line until there's enough in the carb to fire and then idling refills things quick. Sadly modern Vespas aren't gravity fed like the old models so troubleshooting would be easier.

Start at the right side fuel tap (hilariously above the exhaust) and follow the two hoses to the carb. See if any are cracked, brittle, broken.

I had the exact same symptoms on my 1997 Typhoon 50.
It hadn't been used for many years and I got it with 30 miles on it.
Like you I replaced the CDi, plug and lead (no difference) drained the tank, replaced the petcock, fuel and vacuum lines (same).
I cleaned the carb multiple times but in the end I bought a brand new carb and that fixed it.
The compression was as high as any of the Piaggio 50cc's I have (they all run perfectly), cylinder was perfect so not soft seizing.

I think the bowl would get enough fuel to keep it topped up under normal riding, but when it did stints at more throttle it would drain (usually up long hills). It then started fine after a short while.

It could be the petcock, vacuum line.
On mine I think it was a restriction in the carb somewhere.
It's possible your fuel breather is blocked as well so check that.

It could be different on yours as it has a lot more miles but I'd try and rule out a fuel issue first.

In the ET2, the coil is inside the ignition control unit. Basically a transformer that converts lower voltages into much, much higher ones. OK, good.

I think I can probably rule out the fuel line since I just replaced it last July 1st. This is like the 3rd time I've had to replace it in it's lifetime. It always would develop an open crack near the connector. Finally I went big and installed a much beefier fuel line so I didn't have to deal with leaking lines down the road. I'll still make sure it looks ok when I get a chance.

Thanks for the details on the fuel MJRally. I'll inspect.

Gf350: I did replace the fuel tap (petcock) once in it's life because it somehow developed a leak back in 2011. I might have another in my parts drawer.
I don't know where the fuel breather is. I'll need to research that.
What kind of carb did you end up getting. Mine is still the original stock. I'm told they don't make that anymore. Might night hurt to "upgrade" it.

jimc: Ignition Control Unit I think might be the same thing as CDI (Capacitor Discharge Ignition). I did swap that with no change.

The fuel breather runs from just below the fuel cap (under the plastic cover).
You will find a black rubber pipe sticking out from underneath on the left hand side near where the centre stand attaches.

I'm in the U.K. so I got the Dellorto PHVA 17.5 (Piaggio OEM version) from an online retailer here.
This is the OEM for U.K. Typhoon 50 2T, LX50 2T, primavera 50 2T . The U.K. ET2 uses a Dellorto PHVA 12 but it's the same engine. The PHVA 17.5 runs a 53 jet (restricted) or a 60 (Derestricted).
The PHVA 12 I think has a 75 jet restricted.
It's a straight swap on our ET2's but yours use the Webber so the throttle Cable might be a slightly different length?

Honestly I was getting pretty frustrated with it at that point as I tried everything I could think of. I thought it had to be something electrical that played up when it got hot but that didn't really fit as I could drive around for ages stop starting or make it happen pretty quickly by driving up a steep hill.

I'd even replaced the oil pump even though I could see the original one was working. Plus I bought an ultrasonic cleaner for the carb.
Replacing the carb was the last thing to try as the piston and barrel were like new. It worked on mine.

Didn't get around to this project last night. Will post when I can.

Thanks!

Did a little looking around for carb options online in the States. I'm not seeing any Dellorto PHVA 17.5 but I do find the Dellorto PHVA 12. I'm a little carb ignorant. What are the pros / cons between the two? Is one maybe better to use if I were to get a 70cc kit? I also see there's a Malossi 19mm carb kit. Perhaps that's the route one should take?

I'm pretty sure my Weber has some sort of electrical connection going to it like the Dellorto 12 does (see pic). What is that for?

The U.K. et2 has a phva 12 as standard so that will definitely work and would be easy to set up.
The wire is for the automatic choke, that should work fine with the cable there already but might need a new connector on it.
The larger carbs theoretically might work better with a 70cc kit.
There are threads on here about tuning an ET2 which goes into carbs.
Here is one I found useful.

My 50cc Challenge - ET2

!!Success Update!!

First I tried to drive the scoot without the gas cap on. Wanted to rule out the tank breather. It still failed.

The fuel line looked good as it should since it was only over a month old. I wanted to rule out the fuel tap altogether so I created a temp tank via a sacrificed squeeze bottle (see pics). Pulled the line off the ET2's tank and attached it to my temp tank. Took off down the road and it worked! I drove WOT down the straights and on the way back. Not a problem at all.

Since I only had a small bit of fuel the first go, I drove back to the garage and added more so I can take it on a longer test run. As I took off the 2nd time, I could hear and see fuel dumping onto the drive way. "Oh crap, the temp tank came off?" Quickly stopped, popped the seat, nope everything was still attached. That's when it hit me. The vacuum hose was still attached to the fuel tap! I quick engine turn over and fuel came out of the real tank's tap and stopped when I stopped turning it over. But why didn't this happen the first time? Took a closer look at the connected vacuum hose. At the connector of the fuel tap was a crack! Disconnected the vacuum hose, started it up, no more spilling, and it ran just fine during the duration of the 2nd test.

So this vacuum hose MUST be the issue where it wasn't opening the fuel tap valve at higher RPM's? I trimmed back the vacuum hose past the crack and attempted to reattach. Would not go? Why is it not sliding on the connector? Looking down the hose I can see the inside of this rubber outside hose is a hard plastic liner. The liner did not go to the end of the hose so that the pure rubber part could stretch and slide onto the connector. Since I trimmed it back, the liner is too small and will not stretch over. That actually makes sense. If you have a hose where there is a vacuum, you don't probably want a pure rubber hose. Depending on how much suction there is, it could possibly collapse and won't engage the fuel.

Pulled out my ET2 parts catalog and that particle tube is called "Fuel Pipe" part number CM007605. I've looked on the web and can not seem to find this type of hose / pipe. The ones I have seen look like regular hoses. The way they have that one coiled up tells me it does not have the liner. Mine is a little flexible but it's stiff enough to not be able to coil like that.

Anyone have a source for this type of hose / pipe? Would a standard 3/16" fuel line hose (which I have on hand) work?

Thanks!

Standard fuel hose will work.

Great news, a vacuum line is a lot cheaper than a new carb!
I like your solution for bypassing the fuel tank, very inventive.

I just used standard fuel line I think it was 5mm x 3mm where 3mm is the inside diameter. Get the appropriate hose clips and it will be fine.

This kit worked for me when replacing my vacuum lines on a LX50.
https://www.ebay.com/itm/133967472464

I replaced the fuel pipe with a spare fuel line I had and drove for many miles last night and this morning!

Thanks all for the help!