Modern Vespa

Hello brothers

I'm having some issues with My jetting.

Current Setup:

VMC SuperG Fully Ported , 60mm crankshaft
MRP Intake and Reeds - Polini Expansion
Static 18° BTDC
Polini PWK 30mm - Uni Filter
Gearing: 23/67

Idle: 52
Needle: JLJ 3rd Clip
Main: 135

- 1/4 throttle 3rd Gear at 5000~5500rpm i have a solid 290°F
- 1/4 throttle 4th Gear at 3000rpm i'm gettin 300°F
But 4th Gear at 4000rpm or more, the temp just raise slowly til 320°F , if the ride continues temp keep raising

Same distance in each test

Have you considered using a bellows to the frame like original instead of the UNI filter? That would allow unrestricted clean cool air into the carb and might help with the temps and jetting.

Check for a head leak, too.

Where is your temperature gauge located? On the stud or under the spark plug? How far have you tried revving the scooter and watching the temps rise?

Mine is under the spark plug and I like to ride 2 miles wide open throttle to verify correct jetting. If my temperatures stay under 400*F Im happy. I am riding on country roads, no hills, at sea level, warm climate. I dont normally run the scooter that hard, but if I needed to, I know i'll be safe.

If you live in the city, you might not need to jet the same way I do. Jet for the hottest conditions you'll be riding in. That way normal riding wont give you any problems.

After the temperature gauge, the best indicator on how your motor is running is your spark plug color. Once you've settled on jetting, dont forget to look at the plug color to make sure its a chocolate brown.

I just went to this concert.
Once sorted dropped my running temps 40 to 50 degrees on average.

I'll need a longer bellow , the original doesn't have the require size. Let me find one. I don't see any oil around, but i Will check better... If there is a Head leak , why temps gets hotter only in 4th Gear and beyond 4000rpm? Why doesn't happens in 3rd at 5000rpm ?

MJRally the gauge is a ring under the sparkplug. I was testing 1/4 throttle temps before WOT

Maybe something like this?

https://www.sip-scootershop.com/en/product/air-bellow-malossi-phbh-28-30-carburettor_17980200

Your temps seem similar to what I see on my Malossi 225 although I do not have a RPM gauge and my plug temp gauge is analog. I usually see 275-300 cruising at 55 going faster temp rises to 325-350.

Higher rpm under the same load will lower CHT. That's normal.

Maybe you could temp-up the bellows you have (since it won't fit anyway) with duct tape and see how it goes. Betting you'll see an improvement.

Well friends. I'm waiting for a long bellow. Ive been playing with jetting.

When i started to jet this PWK i never did the test without MainJet to GoT sputter in WOT. I just asumed that mj135 was ok because with the SI Carb i was in 125.

Yesterday i got a Soft Seize , so i drilled a MJ to 1.5mm (150) and now it's sputtering. I asume the right size will be 145-148. I did the same Road that Soft seized yesterday and the temps was fine. 300°F.

So, i think i was jetting everything with the wrong MJ size. I'll start jetting from scratch with this mj150

Your jetting sounds fine, you need to focus on ignition timing, compression and squish.
But longstroking a generic 177 is the Frankenstein approach.