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Good afternoon - new around here, but I hit on this topic on a mostly dead thread a couple days ago. Thought I'd start a new topic for general commentary/advice.

First thing - this is on a 2013 Vespa LX 50 4T 4 Valve. Full disclosure - bike had sat for the better part of the last 18 months up until about a week ago, so I am fully aware that this problem is probably of my own making.

Symptoms: Bike electric starts very well and idles down after about 60-90 seconds of running - first time, every time. No issues there. From a cold start I am able to accelerate the bike to full (albeit restricted) speeds - about 39MPH indicated on the speedo. After running it like this for about 3-5 minutes, there is a lag or a hesitancy for the bike to accelerate - but will eventually open up. But after this - 1-2 minutes running with the lag/hesitancy - the bike no longer wants to accelerate beyond 7-10 MPH indicated - essentially stalling at wide open throttle. I can get her to move forward ONLY with very deliberate, minimal jockeying of the throttle. I surmised that is was a fuel flow issue, so I started at the fuel - moved to the carb, and worked my way back from there. I don't suspect that the auto-choke has failed, as it does start well and idles down in a well mannered fashion - but I could be off-base in this assumption.

I have competed the following remedial actions to get her running right again:
- Removed old fuel, replaced with fresh 93.
- Ran with SeaFoam
- Cleaned large and small fuel jets (72 and 35 respectively)
- Inspected and tested the fuel line
- Inspected and tested the fuel tap vacuum line
- Replaced the fuel tap - was concerned that the diaphragm may have been compromised.
- Cleaned Air Filter

So far, nothing from the above has corrected the condition I am experiencing. Beginning to go a little greyer as a result.

If anyone has experienced similar symptoms and can recommend actions beyond what I have already completed, I would greatly appreciate it. For now - I'll just sit on my hands. I have other projects to attend to, but I'd love to get her up and running soonest. Many thanks, in advance!

-JP
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Experiment with placing an ice pack against the CDI . . to deter a potential heat related circuit issue.
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The carburetor likely has a clogged jet, or perhaps a perforated diaphragm preventing the mid stage of carburetion. It should be disassembled, and thoroughly cleaned and inspected.
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tortoise wrote:
Experiment with placing an ice pack against the CDI . . to deter a potential heat related circuit issue.
Thanks! I'll look into this. My thoughts are that if it was a CDI/Ignition Coil issue, it would kill the engine outright after warming. After easing on the throttle - the engine continues to idle/run with small amounts of throttle. But - stranger things have happened. I had a similar issue with an ignition coil in a car a few years ago... I'll further investigate.
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honkerman wrote:
The carburetor likely has a clogged jet, or perhaps a perforated diaphragm preventing the mid stage of carburetion. It should be disassembled, and thoroughly cleaned and inspected.
I don't believe the 4V carb has an onboard diaphragm. Both jets are clear - I tested the idle jet down to .33mm.
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After doing more research and T/S, I'm leaning toward this being a hot CDI/Coil issue. Having trouble locating replacement ignition coil for the Piaggio 50cc 4V engine. Does anyone have a line on where to obtain? Thanks.
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My similar vintage LX50 4V has occasionally experienced a minor case of the same symptoms on hot days this summer. Mine has been run fairly regularly since I got it (new), but only 1700 miles. Usually the bogging is a one-time problem, after a restart following ten minutes of use. Once the bog down is overcome with throttle feathering, it accelerates to a normal top speed and mid-range acceleration. I can't believe the problem is electric. Seems to be related to transition from low to high speed jets or accelerator pump (if it had one). I too would be interested in an expert opinion, recognizing that 50's don't have a large following here!
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Is there anywhere that has an expert on these motors? I'm pulling my hair out trying to get this thing running before the summer ends. But...

Going back to your earlier comments - it could be any number of things. Reason why I am leaning toward electrical issues is because I've hit most of the fuel related issues (short of fully tearing down and rebuilding the carb). I've got some means to test the issue, having access to a nearly Identical 50 4V that I can cannibalize for test parts - I'll be swapping in the Carb, CDI, and coil, one at a time. Once I've isolated it, I'll share my results.
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When mine did that my CDI was starting to fail. We replaced a bunch of things and the CDI was the only thing we could think of. We replaced it and no problems after that. A suppiel on here says he's starting to see more failing CDI'S now that our bikes are getting older. Mine wouldn't start when warm until i cooled it down. Got progressively worse. What year is your scooter and have you ever changed out your fuel and vacuum lines? If not you might want to do them and see if it helps.
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P-Dog wrote:
I don't believe the 4V carb has an onboard diaphragm. Both jets are clear - I tested the idle jet down to .33mm.
It's under the big round cap on top of the carb. If you are not careful, the diaphragm can get misaligned, ripped, or the spring can turn over on itself.

What's strange is that this happens after you warm the bike up. Usually that's valves, but it could also be electrical.

You might try to drain the concoction you put into the tank and go with some good old gasoline from a busy name brand station.
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Motovista wrote:
What's strange is that this happens after you warm the bike up. Usually that's valves, but it could also be electrical.
Count one more for the valves. How many miles on the scooter? Have the valve clearances ever been checked?

Good luck & have fun! 8)
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Ok - some updates after the last round of T/S.

- For everyone's info - nothing but fresh fuel in the tank
- Swapped Carburetor with a known good one of the same make and specifications - stock, AFAIK. Keihin NCV20. Ran well - yesterday in the time I had to let it get warm. But today, same issues came about after running it for about 20-25 mins. Guess I cut the warm up short yesterday.
- Went back to the old carb - swapped out CDI. Stock. No change in performance.

Only thing that remains before the bike goes to the shop for a teardown: Plug and Coil. Probably should have checked the plug earlier than now - but removing the 4V spark plug is not possible with the manufacturer provided plug wrench, as it is a 13mm/1/2" plug and finding a Spark Plug Socket to fit has been fruitless. I'll try a deep socket and a shortie extension, but I'm not 100% this will work with the clearances involved. I'll see.

After that it's the coil, which I'll (unfortunately) have to source myself.

Regarding the valves - less than 200 Miles total on the bike. Hopefully this is not the issue - but if so, it's out of my league. As I said before - if I find no joy in the ignition components, it's going to the shop for the pros to look at. Very close to being done chasing this gremlin.

Thanks to all for your wisdom.
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Motovista wrote:
P-Dog wrote:
I don't believe the 4V carb has an onboard diaphragm. Both jets are clear - I tested the idle jet down to .33mm.
It's under the big round cap on top of the carb. If you are not careful, the diaphragm can get misaligned, ripped, or the spring can turn over on itself.

What's strange is that this happens after you warm the bike up. Usually that's valves, but it could also be electrical.

You might try to drain the concoction you put into the tank and go with some good old gasoline from a busy name brand station.
You guys have any LX50 4V Coils in stock? Can't find them on your website...
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P-Dog wrote:
Only thing that remains before the bike goes to the shop for a teardown: Plug and Coil
Might also inspect the spark plug cap connector and heat-test the pickup coil.
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tortoise wrote:
P-Dog wrote:
Only thing that remains before the bike goes to the shop for a teardown: Plug and Coil
Might also inspect the spark plug cap connector and heat-test the pickup coil.
Will do - I assume you're talking about heat testing the ignition coil - no distributor to have pickups for...
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Good continuity thru the wire and cap. Changes soak plug and ran it pretty hard for probably 15-20 mins. No issue thus far. Have a hard time believing it was just a plug...but...
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P-Dog wrote:
Good continuity thru the wire and cap. Changes soak plug and ran it pretty hard for probably 15-20 mins. No issue thus far. Have a hard time believing it was just a plug...but...
Vespa 7 - P 0. Went back and fired her up... Lagged right out of the gate. Starting to sound like the HV Coil or the valve clearance. Any other thoughts?
⬆️    About 3 years elapsed    ⬇️
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And the answer is...
HI P-Dog
I have the same issue on my 2012 LX50 4V. I'd experienced a similar problem and found a leak in a hose. Fixed it and all was well for 1000 miles.

Now its back. Hoses look good, had the carb cleaned and recleaned by a MC shop, and still the bogging. Next step is to replace the CDI. But just before I do, I'm going to put a new belt on it. The power loss was so intermittent, but mostly when a load was applied as in pulling away from being stopped.

Did you ever get to the bottom of yours?

Thanks
⬆️    About 8 months elapsed    ⬇️
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Hi P-Dog and DBinROC:

New member with a question on an old thread: I have a 2011 LX50 with exactly the problem that you describe, P-Dog. I mean word-for-word exactly the same. Reading your posts saved me a lot of effort in trying things that didn't correct the problem for you.

I kinda suspect the CDI; especially because I just discovered that a recall was issued for our scooters because of potential CDI failure. Piaggio neglected to inform me of this at the time. However, you indicated that you swapped out yours and the problem persisted?

Anyway, just wondering if either of you fellows ever got to the root of the problem (and the fix.) I'd very much appreciate anything that you might offer.
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Hi Woody
I never proved the CDI was root cause although that's still my best guess.

I had the carb professionally cleaned albeit not a Vespa dealer, but a full service moto shop. It's not the carb, but they did return it with a vac tube disconnected. I'd had that problem before which causes a similar but different lag. So I reattached it and all was well.

The original problem presented on a very hot day and after riding at 'high' speed for 30 minutes or so. Based on my research it suggests the faulty CDI. I contacted Vespa US HQ and they directed me to a dealer 200 miles away. My local dealer retired and closed up shop. I googled this other dealer and it was a pretty sketchy operator ( ex-con) with many complaints.

The LX has been stored all winter but I took it out for a spin last weekend. All ran well once warmed up. My plan now is to track down a new CDI. If I remember correctly that recall was not for my LX50 4V. scoot. I'll reach out to Robot at ScooterWest. He seems to know what's going on with all things Vespa. Maybe a Malossi CDI could be used in lieu of stock.

Hope this helps. Let me know what you learn about recall on the CDI.
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Did you cannibalize the CDI as well?

If so I would try to get a brand new one. Cheap considering that testing them on the computer would cost more money than the part itself.

Otherwise you are just going to be going around in circles like me with my 07 LX 50.
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I reported on my similar bogging-down (while accelerating from a stop in high ambient temp conditions) problem several years ago, but never performed any trouble shooting or repair since my trouble was only in conditions rarely occurring in New England, and didn't affect cruising speed, once through he bog. I use it for 2 mile trips, regularly in the summer, yet still only have 3800 total miles. Never not started. Normally runs perfectly.

Is it possible that this occasional, hot ambient air bogging is nothing more than too lean carb jets? Has anyone put in richer jets with good results?
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Hi DB:

Well, I think that my problem is finally solved. After weeks of swapping parts, and much frustration, I finally took it to the shop. Like you, the local Vespa dealer (where I bought the LX50) had closed, so I found a local scooter/motorcycle shop who advertises that they work on Vespas. Unlike your experience, they had good reviews. I can tell you that the good reviews were quite well deserved.

They deep-cleaned the carb, replaced the plug, fuel filter, fuel line, float gasket and needle. Still sluggish. They stuck with it, and replaced the accelerator pump. Voila! They test drove it for 5-6 miles and all was still good. I picked it up this morning and rode it the 25 miles home from the shop. Still running great. BTW, I live in S. Florida and it's hot nearly every day, but mild (80 Deg.) today. They didn't touch the CDI. VERY reasonable price and really friendly and knowledgeable guys. I got lucky.

Regarding the CDI-related recall; I found a Vespa website where you can simply enter your VIN any any recalls will show up in the results. I tried this, and sure enough my 2011 LX50 is listed with the CDI problem. I'm hesitant to post the link (the site might not have the most up to date security) but a search for "recall campaigns Piaggio" should get you to it.

Thanks again everyone for your thoughts and help.
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Fantastic!

That fix makes a lot of sense now that I think about it. I was constantly working the throttle to try to find a sweet spot to minimize bogging. Sometimes I could find a "better" position and make some power for a few seconds. So a faulty accelerator pump might explain that.

Thanks so much for posting your solution. I'll look into that and the recall.

Enjoy your happy grin in the sunshine.
⬆️    About 3 months elapsed    ⬇️
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Anybody have drawing of vespalx50 carb, 2011, I'm having same stall with throttle issue and maybe the carb pump is the issue, but don't know where it's located or how to fix.
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The accelerator pump is under the carb on the right hand side. It's attached to the throttle cable mechanism. so when you twist the gas the pump is like a needle and spurts gas into the carb.

If your having the bogging issue I'd recommend a full cleaning of the carb. It's not hard to do if your u're methodical and label each hose for reassembly. There's lots of videos on ScooterWest and YouTube showing the process. A can of brake cleaner or carb cleaner works fine. Wear gloves and safety glasses when spraying.

Also replace the gas and vacuum lines, the fuel tap (like a petcock) and the air filter. Then use fresh gas.

All these items deteriorate when the bike sits for a while especially with ethanol in the gas. It doesn't take much to clog the low idle jet. That's where I'd start. Maybe $50 in parts.

I taught myself via YouTube so it's not too difficult. 🤪. Glad I didn't spend on the CDI. Doesn't appear to be the problem and they're not refundable. Good luck.
⬆️    About 1 year elapsed    ⬇️
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Final thoughts on bogging LX50
Got the LX50 out of storage. A bit of cranking and she started right up. Rode about 50 miles, no issues.

The more I reflect on the changes I made, I think the top two issues were a clogged idle jet and the diaphragm in the fuel tap were to blame.

For others with bogging issues, clean the idle jet, replace your hoses (they do degrade and generate crud, and check the fuel tap. The latter works on a vacuum draw from the carb. If the tap is broken, it won't feed gas to the carb but it may "leak" when sitting for a while. You can test it by removing ( empty gas tank first) and sucking on the vacuum nozzle. If you can't draw any air, as in opening the fuel diaphragm, then it's busted and needs replacement.

Good luck on your fixes.
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