Modern Vespa

Hey gang, so I bought this "rebuilt" PX200 engine to slot into my Rally and it has a misfire at high rpm, spec as follows

- 210 Malossi Sport
- SI24 with 160/BE3/130 + 50/120
- Standard ducati ignition
- SIP Road 2.0

So I think I've tried replacing everything external on the engine and nothing has made a difference, new stator, CDI, plug, lead, carb, fuel line... is there anything else I've missed that could be causing me trouble.

YT video link below

What is your ignition advance set to? Does problem persist with frame side of the harness disconnected? Spark plug cap tight?

Sounds like pressure test time

18deg. I disconnected the kill wire and yes, same issue. Plug cap is tight, it's an NGK one but I even tried a standard type "claw" one which didn't make a difference.

Yeah, maybe. It goes really well down low, just when it reaches higher rpm it just falls on its face.

Runs ok at low rpm, so sufficiently air tight and pilot circuit normal. There's a lot of fuel spraying in when the throttle is opened. Seems like too much. Main stack not sealing at the bottom? Maybe try another carb; sure you have a few handy.

Thanks Jack.. I thought I did try a different carb but I'll try it again and see what happens.

Put a brand new 24SI on there, tried supplied jet stack 190/BE4/116 and then my combo 160/BE3/130, no good, exactly the same results.. really has me stumped.

https://youtube.com/shorts/GYbOGFuakXo?si=vL3a7y3COoP1Ugp7

Is your plug gapped? Maybe try smaller gap if it is untouched.

I'm so lazy, I never gap my plugs, oops!! In saying that, i never have had a problem with a gap too big? FINYoshi, do you know recommended gap off the top of your head for the Malossi kit? Do you do yours?

I wish it was backfiring. Would be easy then. Everything carb ruled out then. Changed all the external electrics. One place left to go. Stator plate.

Cry cry... I tried that today too, didn't change!!

oh no! Getting short on options. Wasn't backfiring so was only a chance. Also rules out woodruff key sheared. That's the entire electrics changed, except the flywheel itself.

It starts and runs normal and would usually rule out an air leak but weirdness is often an airleak. Quick pressure test would save time there.

FMP has a video on how to make sure the pick up on the stator is in proper alignment with the trigger magnets on the flywheel. Who knows you may just need a few washers to shim things up! Wouldn't that be nice!

?si=fpt1XmQyubnp0olb

Hec

I had similar effect with Primavera and Vespatronic. Gap had to be tighter than out-of-the-box. Vape on my big block is beefy enough to run stock gap.

Okay, so Jack put a seed in my mind to try the factory flywheel. I had replaced it with a SIP touren version before I ran the scooter on the road. Here's a link...

https://youtube.com/shorts/mxuDX_IJxAE?si=qk1ytRmJAn0JA0pL

It's still a little fluffy up top but I put that down to jetting.

Attached are a few picts of the touren flywheel.. yellow coating on the inside which I don't know if that would affect it, also the finish of it is not so smooth.

I wonder if I can get it machined to a smooth finish, but just thinking is there a certain tolerance between the pick up and the flywheel that needs to be maintained?

Great, last thing tried was the issue. The touren flywheel is normally no issue. The problem will be what Hec posted. The height of the pick up will need adjusting.

Yeah, that sounds about right, thanks Jack, thanks Hec. Same though, never normally had an issue with the touren FWs.