Vespa LX not passing over 30km/h
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Lurker
LX 50 4T 2V
Joined: 09 Sep 2019
Posts: 4
Location: Romania
Mon Sep 09, 2019 12:45 pm quote
In the last 2 weeks I read a lot on this forum about what could cause my scooter not to past the speed of 30km/h. Let me tell you how this started.

Being a Vespa enthuziast i found an LX for sale, the money was good and it was a rebuild project for me. When I went to buy it, all that I received was a chassis and 2 bags full of motor parts. That didn`t make me back up because as I said I needed something provocative to do. i started rebuilding the engine and after 2 weeks I succeed in making it start. Now a lot of issues happened on the way.

the first one was the spark sensor from the flywheel. It seems that the previous owner had some issues with the crankshaft bearing, which made the flywheel rotate bad and hit the spark sensor. After fixing this and a lot of other stuff I tried to make a ride test.

The scooter has a nice acceleration but after 30km/h it losses power. what I have done so far:

1. Changed the entire transmission assembly, variator and clutch.
2. Put a new red malossi filte, without oil . I will investigate if this filter needs oil. https://scuter-centre.ro/piese/1755-burete-filtru-aer-vespa-et-et4-malossi.html
3. Tried different adjustment to the carburetor.
4. Cleaned the carburetor nozzle 4 times.
5. I verified the vacuum membrane and also tested that it raises when air enters.
6. I've checked the fuel level.

What I didn`t do and i will try:

1. Change the spark plug
2. Oil the filter.
3. When the vacuum membrane it is fully pressed the main jet is not entirely blocked by the needle.

Any other ideas are welcomed.
Veni, Vidi, Posti
2007 LX 150 (memories)
Joined: 12 Jun 2007
Posts: 8169
Location: New Hampshire
Tue Sep 10, 2019 4:36 am quote
This might help:

De-restrict a LX50?
Addicted
2006 LX150 (carbed) | 2007 GT200
Joined: 29 Jun 2016
Posts: 700
Location: Toronto
Tue Sep 10, 2019 5:06 am quote
Good work on converting a box of parts into a running bike! And welcome to Modern Vespa!

I've never ridden an LX50, but 30 km/h does seem too low even for a small, restricted motor. This post says the top speed should be closer to 60 km/h (40 mph).
Quote:
5. I verified the vacuum membrane and also tested that it raises when air enters.
Do you mean you checked for tears, and that it was seated properly all the way around? Asking because I have seen other examples where an incorrectly seated membrane prevents acceleration past some low speed.

How many miles are on this bike? Maybe it needs a valve clearance check?
Hooked
2006 LX 50
Joined: 16 Jun 2017
Posts: 437
Location: Warren MI
Tue Sep 10, 2019 5:22 am quote
Is there any chance you may have installed the timing chain off one tooth? If not verify the valve clearance is fine. Is the throttle cable adjusted properly to allow the throttle to open all of the way? Is the spark plug wire seated all the way on the spark plug, and firmly inside the CDI? Do you know anybody else with an LX 50 that may let you borrow their carburetor for a few minutes? If it accelerates fine, but has a low top speed, it's almost always the carburetor.
Lurker
LX 50 4T 2V
Joined: 09 Sep 2019
Posts: 4
Location: Romania
Tue Sep 10, 2019 7:12 am quote
So. When i rebuilt the motor I did the valve clearance. And no, the timing is certainly timed )). Another question that bothers me is that the guy that had the motorcycle when he removed the flywheel broke a part of the magnet. From the 3 magnets, if i remember good a part as big as a coin was missing from one. Nevertheless, this should not be a problem when accelerating.

I will try to disassemble the carburetor again and check the mix screw. Because it does not seem to change anything in behaviour when I unscrew it. I will try again to put the wire in the cdi and also on the spark plug. I will check also the resistance of the entire assembly, even though a scooter which has a nice acceleration at low speed, from my thinking, should not have problems with the CDI or something else.

Regarding the vacuum membrane, yes I checked it for tears and also I don`t know how can it be mounted bad, I will take some pictures as soon as i will disassemble the carburetor again.
Enthusiast
LX 50
Joined: 04 Mar 2018
Posts: 66
Location: Winston Salem NC
Tue Sep 10, 2019 3:48 pm quote
The 3 high failure things u might check:
The O-ring on the intake manifold may need to be replaced. Are there signs of the scooter running lien?
It might be the CDI. The problem is usually a shutdown after the scooter warms up, but the stock, US CD! is restricted, whereas the replacement is high performance and not restricted.
I was figuring it might be the accelerator pump, They get clogged.

I'd check those 2 things in the fuel system first.
I had to do my valve clearances twice. Double check that?
Lurker
LX 50 4T 2V
Joined: 09 Sep 2019
Posts: 4
Location: Romania
Wed Sep 11, 2019 6:28 am quote
collinsd65 wrote:
The 3 high failure things u might check:
The O-ring on the intake manifold may need to be replaced. Are there signs of the scooter running lien?
It might be the CDI. The problem is usually a shutdown after the scooter warms up, but the stock, US CD! is restricted, whereas the replacement is high performance and not restricted.
I was figuring it might be the accelerator pump, They get clogged.

I'd check those 2 things in the fuel system first.
I had to do my valve clearances twice. Double check that?
Can you explain me what is the o-ring from the intake manifold?
Enthusiast
LX 50
Joined: 04 Mar 2018
Posts: 66
Location: Winston Salem NC
Wed Sep 11, 2019 10:58 am quote
Mike,

Is there an O-ring between the intake manifold and the engine?
Lurker
LX 50 4T 2V
Joined: 09 Sep 2019
Posts: 4
Location: Romania
Wed Sep 11, 2019 11:58 am quote
collinsd65 wrote:
Mike,

Is there an O-ring between the intake manifold and the engine?
I am asking because I disassembled the intake manifold but no o-ring was there or any gasquet.
Enthusiast
LX 50
Joined: 04 Mar 2018
Posts: 66
Location: Winston Salem NC
Wed Sep 11, 2019 12:36 pm quote
Mike,

I stand corrected. No gasket or O ring. Is it cracked?
A crack will effect idle, but I don't know about speed.

"BRAND
Vespa
DESCRIPTION
Intake Manifold for Vespa LX50 and Piaggio Fly 50

Intake Manifold for 50cc 4-stroke 2-valve Piaggio and Vespa motors. This intake manifold connects the carburetor to the engine. These crack after about 5-8 years and cause air leaks and erratic idle when they crack. This manifold is self-sealing and does not require a gasket. Original Vespa part.

This intake manifld fits Piaggio or Vespa 50cc 4-stroke 2-valve such as:
Vespa LX 50 2006-2010
Piaggio Fly 50 2006-2010"" (from scooterwest.com)
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