Modern Vespa

Hello everyone! I have a problem with my Vespa 49cc ET2, the acceleration is sluggish and I cannot keep a constant speed. Sometimes the engine bogs down when I reach 10 mp/h.

I tried the following but no improvement:
- clean the carb
- change the vacuum and gas hoses
- change the spark plug (it was black)

Also, setting the carb was pretty hard, as on stand, the acceleration seems ok, but under load, the engine is giving up and the acceleration is not stable, or not even revving. I tried to make it lean or rich, but no improvement at all.

As in the image, I have replaced the yellow arrow hoses (vacuum and gas). What's with the red arrowed hose? There is like an air bubble in it. Should I replace it and how hard can it be?

What's the history of this, was it running fine then this started to happen or have you just bought it and it doesn't run right? Is it still bogging after a minute or so of riding?


The red arrow points to the 2 Stroke oil hose that goes from the tank to the pump. The black arrow points to the 2 stroke oil line from the pump to the carb. It's critical this is working or you will be running the engine with no lubrication. (Unless you add 2T oil in the fuel tank).

A few months ago, my engine stalled and as I was in the middle of nowhere, the only way it started was by kickstarting it. I could ride it for 2-3 minutes then stall again. I had to do it like 10 times on my way to a place with mobile signal.


I think it's getting oil as the spark is turning black after an idle run and the exhaust smoke is a bit gray.

Now, the engine is still bogging but somehow not when cold. I could reach the maximum speed and then is going down with an intermittent acceleration. The acceleration is sluggish and the engine bogs down.

If it was doing the same thing before the carb came apart you can rule out any issues with it not being put back together right? Just check the mixture screw is about a turn and a half out. Might be worth testing the choke as well.

It sounds like it's running rich, but the original cutting out and restarting sounds similar to this thread.

ET2 Dies on the Straights

There are other possibilities like loss of compression and electrical issues.

Thanks for the existing discussion, seems something similar. I will look into it and recheck everything one by one, the fuel tap, the vacuum hose, and the carb.

I saw mentioned riding the scooter without the fuel cap on. What should this solve? My symptoms sound like a fuel starvation problem.