Modern Vespa

My 2007 GTS 250 has started doing a weird thing where it will start when cold and run fine, then I ride it for a while, then I turn it off, then when I come back to it, it won't start back up. It will crank and it will turn over and it will run for maybe 5-10 seconds, but then it dies.

Here's what I've tried so far. Apologies in advance cause this gets a little long. Just wanted to provide as much info as possible.

1. Fuel pump (quick and dirty test). How I tested: Pulled the fuel supply line off the fuel injector. Put the line into an empty glass jar. Turned the key on. Result: fuel flowed freely into the jar. Conclusion: fuel pump seems OK at first glance... maybe (but see more info in the What I haven't tried section).

2. Spark plug. How I tested: Multimeter. Resistance read fine. No internal leaks, no shorting. Old plug though, so I replaced it just so I could say I tried it. Replaced with upgraded dual lead version. Runs smoother now, but problem persists. Conclusion: probably not spark plug. Maybe wires or boot, though?

3. Battery. How I tested: hooked up battery to a multimeter and tested static and load voltage. Result: static, 12.67V (not great), turned over scoot, 10V during start (not spectacular, but not decisively effed), with scoot running approx 14V (so voltage regulator and charge system *appear* to be working). Turned off scoot and tested static voltage again. 12.15V this time (on its last legs). Conclusion : Battery suspect. Replaced battery, but problem persists.

4. Fuel leaks. How I tested: started scoot and let it run for a while. Pulled pet carrier out, ran dry rag along all fuel lines and around both ends of fuel injector. Result: rag remained dry with not even a whiff of gas at any point. Conclusion: probably not a fuel leak.

Here's what I haven't done or checked yet.

Deep clean fuel injector. Ordered a kit. Should come this week.

Replace spark plug boot and wires.

Check air supply. Not exactly sure how to do that.

Should probably recheck the new battery with a meter just to make sure everything is still good there.

Gas. Haven't done a lot of riding this year for some reason, so the gas is probably several months old. Since I'm kind of a sporadic rider, I always add stabilizer with every refill, so I feel like it *should* be okay. But maybe not.

Replace fuel pump. My scoot was manufactured during the period where there was a recall on the pump. Symptoms do match what I'm seeing. Apparently, the clearance for the impeller was too tight, and when it got warm, it would swell and seize to its housing. Then when it cooled down, it would shrink and it would work again. I'm kinda leaving this for last for two reasons. 1, it's a total pain to change. 2, it seems weird that it would be fine for 17 years and then suddenly start exhibiting a problem that should have manifested long before now, but I guess stranger things have happened. And if I'm honest, this makes more sense than anything else I can come up with.

Aside from all of that, I'm kind of out of ideas. Anyone have any suggestions for obvious things I'm overlooking?

Other stuff it might be handy to know. I'm the second owner; bought it in 2020. Two years ago, the voltage regulator died and killed the battery. Both were replaced by the local Vespa dealer/shop and everything has been fine since then.

Some good tips below, breather tube seems to be something to look at.

GTS250ie stalling when hot

Thanks flybynight! Some new ideas there. Unfortunately the OP of the linked post never updated with the eventual solution, because that sounds like the exact same problem I'm having. Sent PM to them. 🤞

Next time, just listen for that 2-second "whirr" of the fuel pump when you first switch on, but before trying to start. If no "whirr", the fuel pump isn't working.

flybynight, when you're talking about the breather, do you mean the EVAP?

Going to test that today.

If I understand it right, after a ride I'd open the gas cap and listen for a whoosh of air. Is that correct?

And, second part, it seems in the small amount of research on it that I've done that the evap system is designed to be non-serviceable. Meaning if the problem was a clogged hose, I'd either have to replace the whole thing, or just remove it and figure out how to safely vent the vapor. Correct or incorrect?

Ok. More results.

Wanted to test the evap theory, so I rode it around the block for about 20 minutes until the temp gauge read just above the middle point. Rode it home. Turned it off. Turned it over... And it started right up and stayed running. Huh. Okaaay... Maybe not warm enough. So I rode it around the block for another 20 minutes and returned home. Turned it off. Turned it over... And it started right up and stayed running. Again. Just like how your car won't make the dang noise you've been hearing for weeks when you take it to the mechanic. Anyway, mild frustration that this is apparently a problem that only presents if I'm too far from home to push it back. 😕

Anyway, I thought it would be warm enough to do the fuel cap test. Unscrewed it. No rush of air.

Things get a little interesting here... Just for my edification, I located the charcoal canister. When I examined it, I noticed one of the lines coming out of the bottom is broken. Or maybe cut. There's a fair amount of dirt on the edges of the break, so it seems like it's been this way for a while. The other end of the line terminates at the fuel injector. This kinda looks to my uneducated eye like maybe it was some previous owner's quick and dirty way of defeating the evap system.

Here's a pic taken from underneath.

Yup, the Evap Crap has been circumvented. At least you won't have to worry about that any more.

Just remember to listen for that fuel pump noise every time you turn the key on.

Actually wondering now if it was as simple as some crappy fuel if all is working ok now.

That is the weak spot where the line typically breaks. It is the line from the intake manifold to the cannister. If it is NOT plugged off, it will be sucking outside air causing a lean condition. Whether the throttle body will compansate for this, I don't know.

Eh, I'm kind of a pessimist, so I probably wouldn't go so far as to say that it's OK now. The most I feel confident saying is that it didn't happen today. But could still happen tomorrow. And definitely will happen if I ride it somewhere 10 miles away from home.

Re: the fuel pump; I did check and I was wrong, my model year was not part of the fuel pump recall. So I'm kind of leaning away from that direction now since it doesn't make sense in context anymore.

At this point, I feel like with you all's generous help, I've crossed off most of the likely and easy to check suspects, and basically the only thing left that matches the symptoms is too tight valve clearance. Which for me means that unless someone has a brilliant inspiration for another solution, I'll probably send it to the shop. I'm decent with a wrench, and I'm fairly good at diagnosing problems logically, but I know my limits and I try to stay within them. Basically, I throw in the towel for anything that requires dropping the engine.

Stay within 10 miles seriously wait and see first before spending cash.

But in this case it *is* plugged off. Deliberately by a previous owner.

It is hard to see in that picture, but yes, it looks like it does have a plug in there. Thanks for pointing that out.

I submit for your consideration that:
* the white blob we're seeing there is the far side of the plastic barb, not a plug
* the brittle old hose broke, it wasn't cut
* the evap system should be deliberately removed and plugged, not assumed to have been budged out of the system
* a checking of the valve clearances is in order, as difficulty when starting warm is a symptom of valves in need of adjustment

That's what I'm seeing too.....

Just to confirm the state of the end of the hose, I had another look and the white thing at the end of the hose (looks kind of like a filter of some kind) is *not* currently blocked off.

I just watched a few videos on how to fully remove the evap and that seems like something I can definitely handle. For now, I may just block that hose going the manifold until I have time to do the full removal.

And yeah, I'm going to schedule a valve check. Seems like a safe bet and probably should get done either way since I have no idea when it was last done and I've had it for about 4 years.

Good spot about the white bit not being a plug.

So now the solution may be to properly plug the hose.

I plugged the filter/check valve looking thingy going to the manifold. I had a rubber piece that quite luckily fit it exactly. Haven't had a chance to test ride (rain here today), but it did seem to idle marginally better.

So... Not to muddy the waters too much, but now that we know that there was an air leak, could that have caused the stalls when hot problem?

Since the evap system is pretty much intact, and since I have no direct evidence that the previous owner cut the line intentionally, I'm wondering now if it might be better to just replace the broken hose instead of junking the whole system.

Thoughts?

An air leak will make it run rough, at the least. I find it easier to cut the hose from the cannister about 2 inches away from the intake manifold and plug it there and install a hose clamp too, as plugs can shake loose. That way it is easy to keep an eye on it. As for the rest of the system, you can just leave it in place since it is non-functional at that point.

Just for info, anytime you touch anything that has to do with air fuel mixture, scoot will try to adapt and take a while to settle down.

Another short update.

While I was at the auto parts store today to drop off the old battery for recycling, I decided to buy a short length of vacuum/fuel hose and some clamps to replace the severed EVAP line just to see what would happen.

After removing the original clamps and pulling off the broken line, I could see the hose was brittle and dry rotted as heck so now I think it's more likely that it broke on it's own and was not, as I had believed, intentionally cut by the previous owner.

Anyway, I replaced the broken line and then afterwards, I had time to take it for a short tool around the neighborhood. I honestly wasn't expecting too much, but boy, what a difference! It felt like someone had given my tired but reliable old cart horse some kind of youth serum that turned it back into the wild stallion it once was. So that put a smile on my face.

Rode it around until the temp gauge got above halfway and then headed back home for the moment of truth. Turned it off and then started it back up. It did have some brief stumbles at idle, but it stayed running.

I still think I'm going to have the valves checked just for piece of mind, but I can say for sure that it certainly seems to be running a lot healthier after all the work I've done so far.

I'll try to remember to do one final report back after the valves are done just in case anyone down the road has similar problems and finds this post googling around.

Sound like you fixed the air leak. Congrats!

Just got it back from the shop yesterday.

Have only gone on one medium length ride, but it seems to be back to normal now. Actually, that's a bit of an understatement. It's so much better now than it was when I bought it 5 years ago. And (fingers crossed) the stalling problem seems to be fixed.

It might be hard to say what fixed it because it was at 12,000 miles so I just had the shop do whole recommended service package, but for anyone who might be having the same stalling problem later and finds this post, the primary suspect was the valve clearance, which they reset to spec as part of the service.

Everything done to the scooter is below. Items below with an * are things which seemed like they were possible causes of (or at least contributors to) the problem. The rest, while not specifically related, were due.

Here's everything I did to the scooter:
Check fuel pump *
Replace battery *
Replace spark plug *
Replace broken evap hose causing air leak at manifold *

And here's everything the shop did:
Set valve clearance *
Replaced head gasket
Replaced CVT belt
Replaced rollers and sliders
Clutch pulley cleaned
Clutch bell sandblasted
Cleaned air box and replaced air filter
Oil and filter change
Gear oil change
Inpsected: plug and boot, brake pads + rotors + lines, wheels/hubs, tires, steering, suspension (all fine and within spec).

Also, not part of 12,000 mile service and probably had no effect on how the bike runs, but it was also due for these, so I had them done as well:
Brake fluid flush and replace
Coolant flush and replace

I'm not gonna lie, the 12,000 mile service was pretty dang pricey, and a lot of it probably had nothing to do with the problem, so outside of setting the valve clearance, I wouldn't recommend it as a solution to the stalls when hot problem. But if yours is due, I can say that the bike has been running for 17 years now, and after the service it feels like it could easily make it another 17. So I guess it's your call whether that's worth it to you or not.

One final post.

Went for a 25 mile ride over the weekend with multiple stops and a few uninterrupted 10 mile stretches.

Started right up every time I got back on it, so with everything that was done, this is now (finally!) solved.

Thanks to everyone who chipped in to help. Hopefully this will provide assistance and ideas to someone having the same problem down the road.