Modern Vespa

Hello friends, I just put a fresh gas mix in after not riding for the winter. 5% motul/regular 87. I ran it around the blocks a few times and started losing power. It felt like it was gasping for air if you get my meaning. After bringing it back I throttled the engine to try and work out more cobwebs and the engine started oscillating in RPMs while I was keeping the throttle at a stable place. Attaching a video and it starts about 5-8 seconds in.

https://share.icloud.com/photos/020Af5vl1MPhx_rHSMewEA9qw

I have the feeling Im going to need to do some tuning and parts replacing, but anyone have thoughts?

Im competent with a wrench, but not a mechanic, more like a 4 out of 10.

5% motul? wow!! why so much?

Thats what I read it should be. If not please share your wisdom! Im basing this on the original manuals and other info I have found. However recognizing that gas has changed a little since then...

Though I do go through spark plugs every other day lol

Sounds like: Air leak? Carb float level?

Picture of your spark plug?

Brand new spark plug B7HS.

Where would an air leak be?

Easy: Carb base or airbox connection to engine.
Hard: Engine case seals.

This is the plug I removed today

You are correct… if it's piston ported it should be 5% .

Check the carb base to the cylinder and check the cylinder head before you start sweating the engine seals.

Not sure this helps but here is the manual (in Spanish, of course).

https://www.scooterhelp.com/manuals/motovespa.150S.manual/motovespa.150S.manual.r.pdf

Hello,

I´m not an expert at all, but you may check the easy: clean hole in fuel tank cap, fuel line, points...
Are you using the original carb? If so, it is a son of a ... to fine regulate. You may check the needle in the floater (if it closes correctly), the floater itself (check there is no fuel inside) and the needle position in what we call "the bell" (don't know the name in english part#36). Needle is part #35 in the scheme. This needle usually has 6 positions. Try second or third groove begining from the right side in the picture.

I send you the workshop manual (in spanish...). May help now or in the future.
Good luck & best regards from Madrid (where your scooter was made).

By the way, you may use 4% oil mix if synthetic. No fear. The 5% was for poor quality mineral oils in Spain in the sixties.

Thanks for the great info and your time! Im looking to take a trip to your amazing country and while there get lots of parts!

Sounds like an air leak or you're too lean.

More info:

If I choke it completely, it starts up immediately, and idles fine. I can hand adjust the idle a little bit. Attached is a video with the air cover and choke removed. When it's revved and held at a high RPM it tries to stall. I let the throttle down and rev it back up and it catches up. Next up, to check the float.

https://share.icloud.com/photos/0b9TNvofuCThtYPa-3s_9yx8Q

Also, WAY smokier than usual. Burning super rich or something...

^^^^

So, Im kinda uninformed here re air leak. Where would the air leak be exactly? Is there a part in the reference above where its better to look? I removed the choke manifold completely so that cant be it…

Pull the carburetor and the air box. Replace all of the gaskets with new (greased) ones, torque the carb bolts to 13 lb/ft. Retorque your head bolts to 15 lb/ft, too.

Search on here on how to do a leak down test. That'll tell you where the leak is. Most common area is the carb box where it meets the case. Head leaks are common too.

Alls well that ends well, I used fresh remixed fuel at about 4.6% because the fuel I had in previously was too oily ( don't ask )

Additionally its a good thing I got replacement gaskets for the UA19S1 carb because some were not original and replaced with substandard or incorrect gaskets. took it all apart, cleaned, new gaskets.

Ran the old gas out, much much much better! Runs like a champ... now to fix some wires that broke from the harness...