Modern Vespa

I was gifted an ET4 a while back. It had been sitting a long time. When I got it, it would run fine. Eventually (a couple rides later) it would run and then intermittently die, usually when I came to a stop at idle. The issue got worse and worse and now it wont run at all. When I try to start it, it sounds like wants to fire, but it just wont seem to catch.

I'm pretty sure its getting fuel, I took off the line to the carb and when I crank it over, fuel comes running out of the line so I dont think its an issue with that. Carb is clean. I replaced the rubber manifold to the head from the carb too.

I have not checked the spark plug because its just so hard to get to. I also assume (right or wrong) that spark plugs usually are an all or nothing thing, and the fact that the issue started slow then got worse leads me to believe its not that. I have the plug, how tf do I change it without dropping engine? What tool do I buy?

When I crank it over and give it throttle it sounds different, like it is closer to firing maybe?

What should I be looking at to check? Could it be electrical?

Any advice appreciated, thank you.

nope

nope

A thinwall spark plug wrench.

And it is easier to get to with the scoot off the center stand.

Before you change the plug, have you disconnected the evap cannister? When they go bad the ET4 will act exactly as you describe.

I believe so, but I'm not 100% sure I did it right. I have two lines coming off the rubber between the carb and the head - One is plugged so no air can pass, the other goes to the petcock. The other petcock line goes to the carb. I pulled out a bunch of other parts that used to be connected to that system, but I also just cut some of the lines and left the pieces in there, like the one to the gas tank, which I assume is just a vent (I zip tied it to the inside of the frame).

Does the plugged line go to the carb float bowl? That is a vent and needs to be open to atmosphere. That will cause your symptoms.

The drain at the bottom is not plugged.

It may seem obvious, but it happened to me. I had the key ignition switch work itself toward the off position just enough to have the engine cut out. I could just turn it back to the run position and it would fire right up. Bear in mind that this was only about 1mm worth of play. However, it was enough to cut the engine off.