Modern Vespa

Ok, I have a 2009 Stella 2T that I bought new. I haven't ridden it that much. Only has a little over 3000 miles on it. My last ride was about 4 months ago, and was over 100 miles. It ran fine. I filled up the tank when I got back, so the gas was about 4 months old. A couple days ago I decided to take it for a ride. It started right up with choke, and ran fine after I pushed the choke in after about 20 seconds. I rode it about 4 1/2 miles, and it just died, like it ran out of gas, but there was plenty of gas in it. I got it restarted, but it would only run at idle. Open the throttle and it would just sputter and die. I wound up riding it back home 4 1/2 miles in first gear at idle, in the bike lane. It died several times, but restarted.

I thought maybe the old gas had plugged up the carb, so yesterday I removed and cleaned the carb. I've cleaned a lot of carbs, so I know how. The carb is clean, and I could not find anything wrong with it. When I put the carb back, it wouldn't fire at all. I removed and cleaned the plug, it has a good spark, it has good compression, and when I squirted a little premix in the carb, it would start and run for a few seconds, then die. I did that several times. The idle mix screw is set 2 turns out.

It has been converted to kickstart only. A few years ago I had to replace the stator, and decided to remove the electric starter. It still has oil injection. It has always started with one or 2 kicks and run fine. It was running great right up until it just died. The carburetor is getting plenty of fuel through the fuel line. Yet it seems like it is not getting fuel, but I checked the carburetor thoroughly and couldn't find anything wrong with it. Any ideas or suggestions would be appreciated.

run it off an auxiliary tank/bottle first to eliminate fuel delivery.

but you mention a carb problem, so it's probably electrical

When I removed the bolt that holds the banjo fitting to the carb, disconnected the fitting and opened the petcock, plenty of gas poured out. So it is getting gas to the carb. I checked everything when I had the carb apart. With the carb installed, there is no way to know if gas is getting into the float bowl since there is no float bowl drain. Something changed while I was riding it. It went from running great to barely idling. I thought something might have plugged up the main jet, but everything is clean now.

Electrical seems ok, I have a good spark, and the lights and horn work fine. It's a 6 month old battery that has been kept on a battery tender.

sounds like you might've hung the float needle or picked up some trash in the body of the carb, not the jets themselves.

a quick check would be to pull the air filter off, open the throttle fully and kick it over several times. you should see gas dribbling into the inlet and a bit spraying back. you can also just slightly loosen the top of the float chamber (round disc, single screw) and with the fuel on there should be fuel flowing out.

because it came on after riding my guess is that you picked up some trash or there's something wrong in the system, like a bad breather.

once you've established that you have fuel in the carb you can narrow down delivery of fuel.

from there you can also move on to the electrical.

just spit balling though, will it run and idle with the choke out? you may have a bad clutch side seal. that's a quick and easy check.

Soak the body (not any of the rubber or plastic parts) in acetone/trike overnight then blow out all of the passages with compressed air? Sounds like there might be a goober stuck somewhere.

Everything Greasy Said.

Right now, you're still trying to isolate the fault, so here's what I'd try next...

First off, did you try running it with the gas cap loosened to make sure it's not a plugged tank vent? That's the easiest thing to check and can produce the behavior you described.

Carb-wise, Gas will jellify more quickly than you realize and carb cleaner just doesn't dissolve it. You have to scrub it out, like pressing a micro-bit through the float passage, then hit it with pressurized carb cleaner to get the last bits and also verify that you're getting good flow/spray through.

You could also have crud not just in the tank, but also in the fuel line, that will continue to foul things intermittently, so flush out the fuel line, too, making sure there's no u-bends in it that could hold grit, rust flakes, etc. If you don't have in inline fuel filter, install one. I run one on all my bikes because, honestly, it's easier than keeping the tank sparkling clean.

After that...yeah, you're starting to get into things like electrical, followed by air leaks, but I don't think that's going to be the issue.

You could have an ignition wire that's rubbed through its insulation. The wiring on my Stella all started to rub through before it was ten years old, and you're well past that threshold now.

If that's the case, it will usually spark just fine when tested, but once it gets to revving, vibration will bring the wire close enough to the motor to intermittently arc and lose spark. You can sometimes verify that by wiggling the stator wires where they run from the junction box into the motor and see if the behavior changes, but you really need to pull the flywheel and stator and visually inspect to be sure.

You could also have a CDI that's going bad, but that usually manifests as an inability to rev out, and the threshold at which it occurs will get lower over time until you can't run it at all.

Gas is getting into the float bowl. It will not start at all without pouring a little gas down the carburetor. It will no longer idle. I completely disassembled and cleaned the carburetor, Everything is clean, and as far as I can tell, everything is ok. I have cleaned hundreds of car and motorcycle carburetors without any problems. The Stella carburetor is a little different, but not hard to figure out. I watched Robots video on cleaning a Stella carburetor (ScooterWest)

Whatever happened, happened suddenly. It went from running perfect at full throttle, then died like it ran out of gas, then I got it restarted, it would idle but just barely. It died several times on the way home (at idle) but restarted with one kick. After cleaning the carburetor it will no longer start on it's own. However, when I pour a little gas in the carburetor, it will fire right up, and run at idle for maybe 15 seconds. But it will also rev to full throttle for maybe 2 seconds. It is just running on the gas I poured into the carburetor. But since it will rev to full throttle, that makes me believe it is not an electrical problem. I still believe it is not getting fuel through the carburetor.

I removed the head, and the cylinder and top of the piston look fine. Not carboned up, and no scoring on the cylinder walls.

I am going to put some premix in a spray bottle and continue to spray it into the carburetor and see if it keeps running. If it does, I'm going to take the carburetor apart and go through it again.

I appreciate all the suggestions. I also have a Vespa GT200 on which the carburetor got plugged up with old gas a couple of times, and it would not start. Cleaning the carburetor fixed the problem.

If you've confirmed it's not the tank vent, then I agree you're back to re-cleaning the carb, focusing on the passage from the float bowl to the jet stack.

It's possible to shine a light into the bowl and see it in the bottom of the main jet socket to confirm it's not blocked, but I'm as at a loss as you are at this point.

Main jet blocked, or electrical problem

I'm thinking clutch side seal. They can run perfect then lose all power and not tick over.

Pressure test is the way to check. If the seal has failed or fallen out, running it will damage the cylinder.

Luckily, it's easy to check, though.

OP, remove the breather from the clutch cover, put your thumb over it and turn the motor over. If you can feel pressure, you have a problem.

did you actually rebuild your carb or just disassemble it and hose it down with carb cleaner?

because that's where I'd be looking first.

the good news is that you can check the clutch side seal, compression and tank for any vent issues while it's soaking to eliminate those possibilities.

just a cylinder would be dodging a bullet in that situation!

Ok, I have narrowed it down to the carburetor. There is gas going into the float bowl, but it is not reaching the engine. No I didn't rebuild it, as in with new parts. I took it apart and cleaned it. But I did take it completely apart, and used an entire can of spray carb cleaner. I ran a high E string for a guitar through all the jets and passages. I blew everything out with spray carb cleaner. Everything inside the carb was good, even the gaskets and rubber seals. But something I can't find is plugged up. When I put some premix in a spray bottle and sprayed it into the carb, it fired right up, and continued to run for almost a minute as long as I kept spraying premix in it. It would rev normally. I opened the throttle completely several times, and it ran perfectly, until I quit spraying gas into the carb. Then it died. I probably should have done that to begin with. It had all the symptoms of fuel starvation. There was probably something in the float bowl that plugged up a passage, which is what caused the sudden failure. I'll clean the carb one more time and look everything over with a magnifying glass. I do know all the jets are clean. If it still doesn't work, I'll just get a new carb. There are a couple of passages in it that you can't run a wire through, but when I sprayed carb cleaner into it, it came out somewhere else.

Yes I thought about the crank seal, but those don't usually fail suddenly. I had a Puch moped once with a bad seal on the transmission side. It was sucking in transmission fluid into the crankcase and smoking like crazy. But the fluid prevented an air leak.

before you go buying a new carb let me offer you some options:

1- soak it. not just blowing out with carb clean. soak the fully disassembled body and jets. what you soak it in is up to you. vinegar, pine-sol, actual carb dip, probably not water though.

2- send it to me, I'll strip it, dip it and assemble it and run it on a motor.

3- if it's a 20/20 I'll sell you a known good one that I've stripped, dipped and rebuilt and run on a motor.

4- borrow a known good carb and test it on your motor just be sure. just on the off chance it is something other than the carb.

Thanks for the suggestions. I will soak it. But a new carb is $128, about the same price as having it run through an ultrasonic cleaner. It has to be the carb. There is fuel in the float bowl, the choke and throttle cables are hooked up properly, and it runs fine when you spray gas into the carb venturi. Which has to mean gas is not getting through the carb. There is a little brass pipe in the carb venturi with 3 holes in it. That is where the gas should be getting into the carb venturi from. And if it was, even a little bit, the engine would at least fire. After kicking it 20+ times with the choke on, the plug was still dry. No sign of any gas getting through the carb. As many carbs as I have worked on, I have never had this happen before. That is what had me considering other things. But once I put gas in the carb, it started right up. I did consider a vacuum leak between the carb and box, but the gasket and gasket surfaces are fine, and it was not loose. Even if there had been a tiny vacuum leak, there should have been enough engine vacuum to suck enough gas through the carb for it to fire. Maybe I should put some WD-40 in the float bowl, and connect a high powered shop vac to the bottom of the carb.

Use compressed air to blow the carb cleaner through all the passages too. You may have done that but just to be safe figured I'd mention that as well.

I think your carb is more gummed up than you realize. Those passages are pretty small and they can get completely blocked way too easily.

I'm guessing your float bowl passage is clogged. If you remove the main jet stack, is it dry in there? If so, given that the float bowl has fuel, that kind've has to be the location of the blockage.

And assuming that's the case, if you have a micro-drill, drill it out with a 1mm (~1/32") bit and I bet you'll get some schmutz out of there that looks and feels almost like hardened contact cement.

You can also spray cleaner into the hole in the bottom of the float bowl and confirm that it flows through.

It's all about isolating the fault at this point.

Get a real set of carb wires. Soak it, poke it and blow it. Buy the rebuild kit, too.

Thanks. I have the carb body soaking in Berrymans right now, I'll check that float bowl passage.

I ordered a set of jet wires. I used to have one and lost it years ago, and since I play the guitar, I found guitar strings work well.

I will order a kit from ScooterWest, but I want to get it running first. All the seals and gaskets are in very good condition.

I watched this video from 7:00 to 30:00. Very simple, nothing complicated in there.

That fuel line was like a rock.

Ok, problem solved. It is now running great again. I still have no idea what the problem was except that something was plugged up in the carburetor, and it wasn't the jets. After removing and cleaning the carburetor 3 times, the last time I soaked it in Berrymans Chemtool for almost 24 hours, went through all the jets and passages again with a guitar string, the last time I used a heavier guitar string to run through the float bowl passage, and I could see the end of it down at the bottom of the main jet hole. That was probably it, but I'll never know for sure. It fired up on the first kick after putting the carburetor back on for the third time. I let it warm up, rode it around the block, and set the idle speed and mixture. That is now one clean carburetor. I wish there was some way to drain the carburetor float bowl, like there is on later model carbureted Vespas like my GT200. That would keep gunk from building up on the bottom of the float bowl if the scooter sits for a while. Thanks for all the help and suggestions. They were much appreciated.

I don't know if this was mentioned yet or not, but ethanol gas will cause issues if you let it set. I like to run non-ethanol gas in the scooters, and lawn mower, chain saws, etc...

" I wish there was some way to drain the carburetor float bowl, like there is on later model carbureted Vespas like my GT200. That would keep gunk from building up on the bottom of the float bowl if the scooter sits for a while."

You can turn the tap off and let the motor run until it dies.

I usually do that as part of the warm-up, not the shut down...

It's most effective if you start driving to really get the last bit of gas out