Modern Vespa

2009 Vespa GTS250ie. This vehicle runs great until it reaches operating temperature. Then it bucks, surges, stalls, runs rough, refuses to start until it cools off some…but other times it starts right up. This is what I've done so far; two fuel pumps, check the gas cap for venting, remove the emissions, evaporative system and plugged hose. Check for vacuum leaks. Ran with and without the "pet carrier" installed hoping it would run cooler. New air filter. Checked and cleaned the fuel injector several times. It was never plugged or had dirt in it. New spark plug. Adjusted the valves to specs. Electrical system checked for proper voltage and new battery stays fully charged. Plug cap checked for tightness to the wire and spark plug. Coil, plug wire and cap tested for proper ohms resistant, and they passed. All plug-in quick connectors cleaned and checked for tightness. Different fuels have been tried such as 87, 89, 91 and 93 octane 10% ethanol and ethanol free. No difference. 02 sensor checked for proper ohms resistance and it is functioning properly. While playing around with the O2 sensor, I started the Vespa without the electrical wires connected. Still ran rough and engine check light didn't come on even after riding it several miles. I shut it down and parked it for a couple of weeks in my barn. Two weeks later, I fired up for a quick run to the store, the engine trouble light flickered at idle but underway the light went out. The Vespa ran great when it was cool, and once the engine warmed up still continued to run great! By disconnecting the O2 sensor, I caused the computer to go into a safety or limp mode. It makes the fuel mixture richer. Thanking maybe I missed something on the O2 sensor, I ordered a new one from ScooterWest. Installed and connected it up. The scooter once again, started surging, bucking stalling at operating temperature. I unplugged it and it ran OK again. Concerned it may be running too rich I sent off an oil sample to Blackstone Labs to check for fuel contamination in the oil. Paperwork came back stating it just had a trace amount. Nothing to be concerned with. I continue to ride it this way. However, the other day I rode it to a business and parked in a large asphalt parking lot with half a tank of fuel. 91° day. Did some shopping and came back out, and the scooter cranked, but would not start. I pushed into the shade pumped about 2/3 of a gallon of cool gas into it. Crank but no start. Burning my hands I managed to disconnect the spark plug wire, and it had spark. Reattached it and pulled the fuel line. It was getting fuel. Still crank but not starting. Let it sit for a while longer while I made a phone call. Finish the call and it started right up And carried me home. What gives any ideas? What should I check next?

paging Bill @WLeuthold to the lobby help desk phone. Your expertise is needed.

Is it possible that it has a malfunctioning temp sensor. The FI thinks its running too hot. ?????? Shutting it all down until it cools off/ resetting the brain.
Or an air pocket in the cooling system is stuck somewhere not letting it burp. ??

Im just spitballing here. you have already done nearly everything possible to troubleshoot this issue. Im scratching my head.

Good idea about burping the cooling system. But I've already done that with the air bleeder valve. Positive there's no air in the cooling system. I'm not familiar with the temperature sensor other than the temperature sending unit for the instrument gauge dash cluster. Temperature indicator runs in the middle of the range. Also with a handheld infrared temperature unit from Harbor freight temperatures within the "pet carrier" area are about 136 degrees. I'm sure they were hotter when I broke down in the parking lot! Appreciate your input.🛵[/img]

All I can think is the CDI unit going wonky, but I don't know this machine. It may have a CDI or it may all be controlled by the ECU. Sorry I could not help more.

Thanks Tierny and Donttellmywife. Scooter now has 15,000 miles on it. Problems started at maybe 7,500 miles and two years ago. Also cruising along at highway speeds it suddenly feels like it dies then instantaneously resumes as if nothing was wrong…its more than bucking…more than surging. This lasts milliseconds. Took it to a well established multi brand and Vespa dealer. The service technician plus the service manager couldn't find any problems. I doubt they even rode it long enough to warm it up. Same dealer couldn't find any fault with the rear disc brake. It was spongy and wouldn't lock up the rear wheel. I was informed all Vespa's rear brakes are like that. As I wanted this fixed too. Said I knew better. I even got the owner involved. He listens and backs up his employees. I asked if they were Factory trained…yes. I asked if they passed the final quiz…no one answered . They said nothing is wrong and if I wanted they could 'throw' parts at it. But why do that when nothing's wrong? They know me. I'm a MSF rider coach and advise my students if they are looking at a used bike to get it inspected by a professional mechanic…them. Well not anymore. I don't want one of my students injured or worse on a bike that is certified as operating normally.
Trailered the scooter home and watched a ScooterWest Robot video on how to bleed rear brakes. I actually built a vacuum pump and managed to suck the air bubble out of the brake line. Now I can do an emergency lock up with the rear wheel, even though they supposedly don't by factory design. So now I don't trust dealers because of this AND troubles with a Yamaha dealer who I have been doing business with since 1978. My 2003 V-Star has 80,000+ miles on it. Wouldn't start. His technician says the ECM is bad and the part is no longer available. Takes two months to diagnose this. A used one is installed. $478 later I get the bike back. I go over it. Loose positive battery cable. Mismatched bolts and screws that were lost. Speedometer cable barely screwed into the front wheel. Tires severely under inflated. Even the ECM was just tossed into its housing and not bolted down. Throttle cable routed wrong causing the throttle to stick open. As I stated they had it for two months… Led a ride to a neighboring city for lunch run. Came out and the V-Star wouldn't start…then it suddenly did. Continued not starting then randomly starting that weekend. Took it back to the shop and the owner didn't want to work on it again…nor refund my money. He said, "As far as I'm concerned your bike is fixed. It wasn't running when you brought it here now it runs". I added 'runs sometimes…' I found a new ECM (electronic control module) from an aftermarket supplier in California. Bike runs great now.
Took the Vespa to an independent dealer who said he could fix it. Charged me $40 and didn't fixed it. Vespa dealers want anywhere from $130-$150 an hour to diagnose the Vespa problem. They charge one hour minimum. If they don't diagnose within the first hour, they pro-rate it if it takes less than the second hour. If they still can't figure it out, the charges just keep going. In other words, you're paying them to learn to work on your bike. I appreciate any and all advice from this forum. I really enjoy the Vespa when it runs properly. No other scooter's ergonomics fit me. Thanks again for your help.

Try cleaning the throttle idle bypass port with some carb spray (remove the intake hose and look for the small hole next to the throttle butterfly inside the throttle body). Other than that, possibly your fuel injector might have a crack in it? This is a puzzle for sure.

I want to agree with the above post about the certainty of the injector's status.
It can be cleaned\inspected but does it operate within limits at operating temps? I chase that theory cause it runs perfect when cold. When it gets hot, internal electrical continuity breaks down making it sputter. Just like the injector\coil packs on my Chevy truck.

Then I also wanna chase after the theory of the wonky ecm at operating temp.

I just recently replaced the ecm of my Goldwing ($850) cause the overheated ecm would trigger the FI light. Those are encased in a hard thermal barrier resin that breaks down after years of service. So normal temps make it store the code.

Still scratching my head for ya on this.

Putting my money down on "cracked injector" and crossing my fingers for ya.

If you go down this path, note that Piaggio-compatible injectors can be sourced very inexpensively using generic part numbers - as long as you only need the injector, and not the proprietary bracket.

The injector for my 500ie is a $30 generic part. With the bracket it is $210 and a two-month wait from AF1Racing.

This is making me rethink selling my spare GTS250ie...

You mentioned a barn, any chance of a rat chewing on a wire somewhere? No signs of droppings around the bike / nests under the floorboards, etc?

You didn't mention a fan, but I'm assuming you've heard it running?

I had a similar problem with my 2009 GTS250.

It turned out to be the spark plug lead. It goes from the battery compartment and comes very close to the exhaust, and the insulation melted. That caused an intermittent short after the scoot would heat up; especially when I went over bumps or sat down hard.

The solution was to replace the lead with a slightly shorter one that wouldn't rest on the exhaust. And also, to wrap extra insulation around the section of the lead that comes near the exhaust.

That was my thought as my 2006 GTS would just die on me. A bunch of folks including AF1Racing looked at it. AF1 found some cracked fuel lines they replaced and that helped briefly but returned a few hundred miles later. It was an independent shop owned by a previously certified Vespa mechanic who found the cracked injector and replaced it. That was when the scooter was 11 years old. So in addition to checking your injector, spark plug lead as that's a known trouble spot I'd so ahead and change the fuel lines. Small cracks could be contributing to your issue.

I'll get back to work on the Vespa soon. Thanks for all your suggestions. Decided to work on my more simple 96 year old car. Had two out of four spark plugs not working. Don't understand, they were only 23 years old with low mileage. Car restored in 2000 just in time for the big "millennium bug" computer crash…that never happened. Thought this and other vintage vehicles would make good apocalypse cars. Champion plugs were replaced with Autolites and now it's firing on all 4 cylinders. A local parts store actually had them in stock. Plugs have 1/2 inch pipe thread, no gasket or tapered seat.

Okay. Back to the Vespa. Checked the fuel injector and it is in fine shape. Working great no cracks. Also took off the intake manifold where it bolts to the cylinder head. No air leaks around there, but I put some high temperature silicone sealant around it and let cure for a few days. Fired up 2 1/2 days later and it's still acting up surging bucking not idling right. Not sure what my next move is going to be. No mice in the barn to chew on the wires. Plus I have barn cats that take care of any of that type of problem. I call it a barn but it has a concrete floor and it's sealed up pretty good. Has heat and Roku TV out here. I can watch ScooterWest videos all day long. Oh, and something else to add, I got my coil and heated it in the oven at 170° to make sure it wasn't breaking down under heat. Still tested good.

Maybe its time to put my Vespa out to pasture…

Have you had any progress in the investigation ? I'm still curious why it does this. It is possible mine might have these same issues some day. Please don't give up on her.

NEW PROBLEM just now. Headed to town on this 79* Fahrenheit day. Engine is warmed up to normal operating temperature as I approach a stop sign. I roll off the throttle and the Vespa starts slowing down with compression braking…then the engine speeds up maybe an additional 750 RPM, enough to be noticeable so that I'm not slowing down…then the compression braking takes over again as the RPMs decrease…then the RPMs increase again maybe an additional 750 and I'm not slowing down…and this cycle keeps repeating itself again, then again, then again and so on. I stop and can feel the engine idling fast enough that it's barely trying to pull itself. The RPM gauge indicates one additional bar…instead of 1,500 RPM maybe 2,250. At the next stop it's running okay. At my destination as I park it it's idling fast again. Take care of business at the museum maybe 30 minutes. Vespa starts right up and continues okay though on the highway at 50 mph I can still perceive a slight 'surging' sensation. Made it home and now I'm sharing my story. HELP! Again please…
Dontellmywife; about traded for a Zuma 125 except I don't fit comfortably on it.

When you replaced the fuel pump, did you use the OEM pump or those little ones you plug into the existing fixture?
Also, what size battery is in the bike now?

Went with aftermarket fuel pump by itself first. No change in performance.Had an aha moment and ordered the factory original fuel pump assembly. Still no change. Ran the same with the original fuel pump, aftermarket fuel pump. And genuine Piaggio fuel pump. Absolutely no difference.
Something else I didn't mention is when I am surging down the road at anywhere from 30 to 60 miles an hour, when I crack the throttle wide-open and accelerate, it runs like a bat out of hell. No skipping, no surging, no bucking. Just smooth linear increase in speed till it runs out of breath at nearly 80 miles an hour…top speed. Does this additional information help? Thank again.🤔🛵

My Burgman 400 did the same high idle symptoms. It was a bad idle air control valve. It made the FI light turn on a few times. Replaced it, calibrated the new one. Good as new. my old Yota truck did that as well.

Your Ecm has to be corrupted, sending Wrong\bad signals to the injector. Something internal in the brain \FI manifold. I can't see anything mechanical causing it to run that way. It has to be a programming, computer brain issue. I'm not saying you should burn money buying a new brain box, but everything points at it. I dispise wasting money on parts that didn't fix it.

Hope somebody will chime in that has already dealt with this same problem.

This is real head scratcher.