Modern Vespa

Since last post about the fuel filter/ vacuum tap, I've gone thru and replaced EVERYthing- gas lines, vacuum lines, new clamps, new t-connector- and no change.

I even put in fresh gas, checked the plug, checked the air filter/intake.

Still, it'll start, it'll idle just fine...as soon as I turn the accelerator, it just 'bub-bub-bub's. If I let go of the throttle, it'll go back to normal idle.

I've got a minute long video demo, but appearently it won't post as an attachment here.

Back to the drawing board-
Any other insightfully ideas, before I take it in and see my 2 week paycheck disappear?

you clean the carb yet?

I have had exactly those symptoms on an LX150 with a clogged carb jet.

Sounds like the carburetor's idle jet isn't blocked, but it's main jet is.

Did you do all that work before cleaning the carb?

Did you happen to install a in line fuel filter?I installed one on a LX and it would not accelerate.

Maybe Greasy or someone else with more wrenching experience than me can help on this one...

I know this isn't great for the motor, but I'd spray the ever living shit out of the air box with some carb cleaner while ripping the throttle.

If it doesn't cut out with the spray, I'd say it's not getting gas because that jet is blocked.

Does this make sense?

Yeah. Don't do that.

All of the above- cleaned it out spick and span-

Didn't put a fuel filter in a n the gas line....
Sorry; just woke up from a nap. They've got me on Midnights now- arg.

when you say that you cleaned it, can you please elaborate?

my guess is that you've got something assembled incorrectly or a little piece of gunk trapped up in there somewhere.

Well, you getting gas to the carb, it's idling good, throttle up - no good. So, take the carb off, clean it, check the jets for blockage, check the diaphragm for any holes/tears, make sure the bowl vent is clear, etc..... You will find the problem. While you are taking off the carb, check the rubber intake manifold as well. Good luck

Some people catch the float while removing the float bowl (me) and knocks the float height out of adjustment. Check that while you're in there.

Does this engine have a vacuum fitting on the carb intake at the front?

This sounds like it could be an immobilizer issue because it stops revving as soon as it gets off idle.
In this case, I might be tempted to use a bit of ether to see if that can get it past 2000 rpms. If it doesn't, it might be that the antenna is disconnected, or the key isn't programmed. If it does, it's more than likely fuel.

You can sure learn a lot on this forum.Thanks

LOL fair enough, but, strictly theoretically because I'm curious.... Would it work?

yes, it should.

besides screwing up your airbox, the filter, all the shit around it and getting a bunch of carb cleaner on the ground and wasting it. no, it would not provide any tangible results that could help you diagnose the problem.

Womp womp

Could this be caused by an incorrectly set fuel mixture screw?

a remote possibility, but a possibility none the less. my money is on incorrect assembly, not throughly cleaned, bad gas or immobilizer.

Yes, check this carefully. The problem is, it's hard to tell what the "right" setting is without another carb to compare it too, and I don't know the proper float height to suggest. You have to bend an L-shaped metal tab to adjust it, and there is a little tab-within-the-tab that toggles the needle valve. Both of those have to be right.

If the float is set, or is hanging up on something, so that it rides too high, the fuel in the bowl covers up too much of the base of the main jet. The carb slurps in too much fuel and essentially drowns the engine in gas. This could be your problem, and while it may be counterintuitive, this has nothing to do with the fuel mixture screw, which only deals with the mixture at idle - which seems to be fine.

If the float rides too low, it keeps the needle valve too closed so not enough fuel comes into the carb to replace the fuel being used, and the engine runs out of gas once the fuel in the bowl disappears. After a little while the engine will start and run just fine again as fuel dribbles into the carb - which is obviously not your symptom.

It is also possible that the rubber coating on the tip of the needle valve isn't sealing properly against its seat, allowing too much fuel to dribble into the carb. You didn't happen to scrape that coating off when you were cleaning the carb, did you?

And the there is the issue of the rubber boot on the other side of the carb. If that is cracked, or twisted, or kinked it can cause all kinds of weird behavior above idle like this. Check that carefully for integrity. I had some kind of a kink in mine once and the scooter wouldn't go above 20mph. Took me a long time to realize that this had nothing to do with the jetting, fuel, or throttle.

Is the inside of the carb stating to corrode? Was there white dust like stuff inside of it when you pulled it apart? Here's why I ask.

A friend offered to help a neighbor to get his daughters Vespa running, so the guy can flip it. Once his daughter graduated she just let the Vespa sit until her dad realized it was still in the garage. The friend bought the carb to work so he could use our industrial cleaners. The carb was soooo corroded inside! Just a terrible mess. Nothing really stops it because once gas get inside the carb it dissolves any corrosion inhibitor you can think of. The Vespa owner didn't want to spend money on a new carb so he just sprayed it with WD-40 and put it back on the scooter. The guys intentions were to flip it but if he was keeping it he should have just purchased a new carb. Chasing your tail with a corroded carb sucks.

So how old is your LX? How long has it sat inactive? Was there corrosion inside the carb when you pulled it apart?

Are you saying you have cleaned and reset the carb? Jets, bypass, etc? How did you do it? I ask as even my dealer has sometimes needed 2 or 3 tries with an ultrasonic cleaner to get it right. That is why I personally prefer fuel injection. A carb can be a finicky beast.

Update-
Carefully pulled the jets, cleaned the shit out of them and their home...jets are definetly clean; as well as set right-
As far as the float; I seriously doubt it..not to say it isn't a remote possibility, but I was out riding, and after about 20 miles, it conked out; luckily smile from home-
Carb
So far- here's what's been done-

Replaced vacuum fuel tap, checked before installation and it worked-

New vacuum and fuel lines with proper hose clamps, from dealership.

new 3 way barbed connector-
All connections double checked and right-

Carb pulled, jets pulled and blasted out with carb cleaner- light visible thru holes, put back as they were removed- their slots also blasted out- checked for corrosion; nothing.
Went back a second time to make sure-

Checked accelerator pump; she squirts.

Checked spark plug and connector; strong spark and clean.

Pulled the hose off the air cleaner, no change, so it isn't a dirty box.

The transponder blinker is blinking as it has, same single blink, start up the bike, she shuts off.

I'm boggled at this point-
Been (greatfully) writing back and forth with greasemonkey-

Below is a YouTube link to what's going on. I tried posting it in attachments here but it doesn't seem to want to add it.

https://youtube.com/shorts/xXfZtL0HNo8?feature=share

Restriction in the muffler assembly

This is probably off the wall remote but when you give it throttle, does it seem like it bogs down? I am wondering if the driveline is somehow jammed up and when you goose the gas, the clutch engages but pulls the engine down because it can't move.

On the vid you put up - was this a cold start? If so, you need to let it warm up some. Once the auto choke is disengaged, it should not have any problem accepting some throttle. Now if this is a cold start, I would check your valves and see if they are out of spec.

Getting into check valve specs is WAY out.of my league-.and have nestly I don't have a great place to tear it down- just a shared driveway-
I'm in agreeance with something being wound around the drive unit-
It makes total sense, but unfortunately I don't have the means to get down and tear off the cover.

I'm gonna have to wave the surrender flag and take it in-
Hopefully it won't cost me a kidney and they'll allow payments-

Pressure seems fine; was running great for about 20 miles and died.

This sounds like it makes the most sense at this point-

it's highly unlikely to be something in the driveline.

okay, so it starts and it runs. and it's not the immobilizer.

you've checked the cap. have you checked the plug and the air filter?

because it idles, I believe that it is something carb related. when you cleaned the carb did you blow out the idle circuit as well (ie take out the a/f mix screw? and blow it out with cleaner and compressed air?)

from there, I'm kind of at a loss. you rode it 20miles and then it conked out is just odd.

after it conked out did it restart? when it's done so in the past does it restart immediately?

we are rapidly approaching the end of the runway on diagnosing something over the interwebs so taking it in may be your best option after another round of having a look see at items.

I took the airbox hose off while running, opened the throttle and hit it with a short blast of starting fluid- about 1 second- still no change. No rev; nothing.

I'm just bumming out because I'm generally able to diagnose and fix something, and this LX is the first nice thing I've been able to afford in over a decade, and had it out 3 weeks and kablewy

Missed the fuel air mix- I just got the jets blown out...

I'm outside about to check that right now.

Plug and cap was fine, spark was good...

Yep. After it conked out, it started right back up. Gave some gas, and she just bogged. Been the same sense. I'll message you once that's done. It stalled once earlier, and took a few minutes to fire up again, but the second time was when it left me stranded. That's what's got me scratching my head- ran fine and whoop.

Ok- going by the pic I've pulled up, I'm seeing a threaded hole without seeing anything in it to screw in or out- I didn't touch those, so it may be possible it wriggled out...
Screwdriver is pointing to the hole

That's for either a heater or a TPS, which you don't need and won't cause this issue. When you sprayed the ether, did you also hold the throttle open? I'm trying to find out if it will rev up with the throttle open and ether.
Also, check and make sure the needle in the slide is going down into the hole. I've seen those get lodged to the side, so they aren't going up and down. Also, check and make sure the diaphragm is not torn, and is correctly positioned, and there is nothing sitting above it.

find a bottle that you can stick a hose on to, and fill it with gas, then hook the hose to the carburetor. Make sure the bottle is vented so gas can flow. When gas flows down into the carburetor, try to start it and see if it does it's thing or something else.

Yep- had it wide open throttle- nothing. The slides fine, too-

That really does sound like an immobilizer issue. It definitely should have revved up with ether.