LX 50 Issues
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Member
Vespa LX 50
Joined: 19 Sep 2020
Posts: 7
Location: New York
Sat Sep 19, 2020 5:29 pm quote
I recently bought a used 2006 LX 50 4T 2V with ~5k miles. It has worked fine, but idled rough and seemed to lack power (more than a typical 4T). Oil was a bit low when I bought it so I'm not sure it was always well kept.

I decided to do a bit of upkeep, so went to replace the spark plug and check valve lash. The valve lash was off (loose) so fixed that up to 0.10mm in / 0.15mm out per the workshop manual specs. I did a quick test ride and it seemed to run a bit better. I went out later and it had almost no power at all.

Right now, it idles great, but occasionally will stall. If I give it throttle, it may stall or hesitate, or I get good rev, but no power to the wheels (almost no movement when on the ground).

Here is what I've done:


    - Re-checked the valve lash (probably 8 times at this point), made sure it was TDC on both flywheel (second notch) and cam markings (line). The markings do seem correct. I unfortunately did not keep the original lash values.
    - Tried both slightly tighter and slightly looser valve lash with no success
    - Swapped in the old spark plug and checked gap (0.75 on the new, 0.9 on the old)
    - Completely cleaned the carburetor (idle jet was clogged but everything else seemed fine)
    - Cleaned and re-oiled the air filters
    - Replaced fuel and vacuum lines (they were looking a bit old)
    - Checked for leaks as best I could
    - Oil replaced and filter cleaned


I don't have the equipment to check compression. Does anyone have an idea of where I could look next?

Video here (this is about a minute after cold): https://1drv.ms/v/s!Al3CQyGP5qmKnMEEVtXZBSnLwDcTuQ?e=iNGbns
Enthusiast
GTS 300 70th Anniversary
Joined: 12 Mar 2020
Posts: 79
Location: Scarborough UK
Tue Sep 22, 2020 1:17 am quote
I feel your pain with these little project bikes!
Just a thought, have you checked the belt and clutch? Just wondering if these are slipping are not grabbing like they should. Other than that you have done everything I would have checked.
Member
Vespa LX 50
Joined: 19 Sep 2020
Posts: 7
Location: New York
Tue Sep 22, 2020 4:26 am quote
Thanks for the response!

I suspected this and pulled off the belt cover over the weekend and everything looked good. I have the tool needed to pull off the clutch bell coming tomorrow so will check the pads and clean everything up.

I'm still going to replace the belt and rollers and also ordered a new fuel tap, intake manifold and CDI. I'm also going to check compression, although I was able to get a nitrile glove put over the plug socket and did have pressure when I spinned the flywheel.

What's weird to me is the stalling with throttle and rich smell, which wouldn't be affected by the clutch. The clutch would explain the wheel power, but the timing is just really strange
Veni, Vidi, Posti
Lx 50 4T, GTS 250, S 150 (Missing in KS), Something Chinese, GT 200 (sold)
Joined: 21 Feb 2011
Posts: 8912
Location: KS USA
Tue Sep 22, 2020 5:19 am quote
I have your exact bike and I can tell you that they are pretty finicky. That's all I can say to you an offer moral support. Just know you're not alone! Mine seems to have a problem with cold start and it gets worse the longer it sits. I have actually put on most of my spring and summer miles on it. I hope you can find your problem and fix it. And keep us posted. Good luck.
Addicted
GTS 250ie Super, Italjet Velocifero, Scarabeo 150, S50,ET4
Joined: 22 Nov 2016
Posts: 516
Location: Winston-Salem, NC
Tue Sep 22, 2020 5:23 am quote
Sounds like a carb issue. How open is the throttle when the bog happens? It sounds like it happens as you come off the idle but I could be wrong. If it happens as you come off the idle its probably the A/F screw. It could also be that the diaphragm isn't seated right or has a hole in it. When you checked the CVT was everything turning properly? When you rev the engine on the stand it should spin the wheel unless something is locked up. Make sure when you turn the clutch the wheel spins. Be sure that when you grab the outer edge of the clutch pull the pull opens up. All things to check out.
Member
Vespa LX 50
Joined: 19 Sep 2020
Posts: 7
Location: New York
Tue Sep 22, 2020 2:17 pm quote
Thanks Pinkscooter, these are all great suggestions.

I re-seated the diaphragm (visually no holes, but the seal seems a bit small so its possible it didn't seat quite right) and it now revs without bogging down. It's still a bit rich, so I'll adjust the A/F when I get a D bit.

Still has limited power to the wheels. I can't make it up a small hill near my house, but at least the scooter moves now

On the CVT: the front pully, rear pulley and clutch bell each turn fine. If I spin the clutch bell, the wheel does spin, but it's possible its slipping on the pads. I'll pull off the clutch bell and see what I can do.
Addicted
GTS 250ie Super, Italjet Velocifero, Scarabeo 150, S50,ET4
Joined: 22 Nov 2016
Posts: 516
Location: Winston-Salem, NC
Tue Sep 22, 2020 3:37 pm quote
Those pesky diaphragms. If you don't get them in right they cause a world of trouble in your life. The same goes for carburetor diaphragms. Don't expect any great performance out of an LX50. They are not rocketships to say the least. Are the restrictions out of it? I don't know what they doe but a well tuned CVT can help these scooters a bit.
Hooked
S150, Beo 500ie
Joined: 14 Aug 2019
Posts: 365
Location: Bermuda
Tue Sep 22, 2020 3:54 pm quote
The engine sounds good enough to me to get power to the wheels.

But with a 5k mile scooter that's 14 years old, I'd absolutely expect the belt to be worn and/or slipping, and the rollers to need a close inspection and probably replacement, and I'd clean out the clutch. I would absolutely replace the belt and rollers before concluding anything else about an engine that seems to be generating RPM.
Member
Vespa LX 50
Joined: 19 Sep 2020
Posts: 7
Location: New York
Tue Sep 22, 2020 4:00 pm quote
Yeah, the weird thing about this is it was basically working until I messed with the valve lash, so having a clutch failure at exactly the same time seems like horribly unlucky timing. The scooter did make it up that same hill easily prior, so not expecting it to zoom up there, but it should be able to clear it (it's probably a bit more than 15 degrees).

It's a US 4T 2V, so I don't believe there are any restrictions on it out of the factory.

I ordered some sliding rollers and a belt, so will get those thrown in and clean things up. I'll let you know how it goes, thanks for the help!
Member
Vespa LX 50
Joined: 19 Sep 2020
Posts: 7
Location: New York
Mon Sep 28, 2020 5:23 pm quote
OK so did the following:
    1. Replaced belt (Piaggio) [old one looked pretty good for age]
    2. Replaced rollers (sliding, 6g) [old ones looked pretty good]
    3. Cleaned clutch and overall transmission [a bit dirty]
    4. New air filter (hey why not)

Also adjusted carb air/fuel and idle so that's better now. Going back to look at valve lash again
Member
Vespa LX 50
Joined: 19 Sep 2020
Posts: 7
Location: New York
Sun Oct 11, 2020 8:58 am quote
Still no luck here, but a quick update:



    1. Tested compression, 130psi using kick starter and held steady for ~10 minutes
    2. Replaced the intake manifold
    3. Opened up the carb again, idle jet was partially clogged already. Going to order a new diaphragm since the seal doesn't quite line up.
    4. Replaced fuel tap (the old diaphragm seems sticky)


It idles great, revs on the stand nicely, but when I set it down on the ground, it barely moves on flat ground. That said, even on the stand it doesn't seem to be hitting higher RPMs. I haven't gone back to valve lash but given compression is "ok", would this be an issue?

Here's what it sounds like now: https://1drv.ms/v/s!Al3CQyGP5qmKnMJNKjP8LUvFAocF4A?e=pgQZIk
Hooked
S150, Beo 500ie
Joined: 14 Aug 2019
Posts: 365
Location: Bermuda
Sun Oct 11, 2020 1:39 pm quote
Vexing. It would be nice to be able to borrow a working carb to troubleshoot it as a whole.

Iím a little suspicious of the re-fouling of the carb. If the fuel system is properly clean that shouldn't be happening. Other passages in the carb could also be plugging up.

Iíll share with you an situation I just solved myself, with an engine that was running seemingly fine but that had obvious problems stalling when idling and (though I didnít notice it) was struggling at the top end too.

It really seemed like a fuel or fuel delivery problem, but the issue turned out to be a bad connection to the coil. Didnít even require a part, just a cleaning and reconnection. Quick to check on the 50, unless the coil itself is the problem...which seems unlikely.
Addicted
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 526
Location: Deepinnaharta, Texas
Sun Oct 11, 2020 1:59 pm quote
Greetings:

If all that fails, search for "LX50 CDI" using the Forum function for tales of this generation of Engine Control Module failures.
Addicted
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 526
Location: Deepinnaharta, Texas
Sun Oct 11, 2020 2:03 pm quote
Knew I'd Seen It SOMEplace!
Greetings:

Here's the link I recently read about. Sound Familiar?
Member
Vespa LX 50
Joined: 19 Sep 2020
Posts: 7
Location: New York
Sat Oct 17, 2020 7:35 pm quote
I ordered a new carb, threw it in and the scooter now runs perfectly.

I'm guessing the diaphragm was damaged in some way. I may try to see if I can get the old carb working when I get some free time.

Thanks everyone for the help!
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