Modern Vespa

Hey all, I've got a 65 Li150 and I've installed one of these PHBL carb kits - https://www.casalambretta.us/index.php?route=product/product&product_id=2206 from Casa Lambretta.

Goodness was it ever a f-ing pain to get this all together. I had to drop the engine, file the intake so it would fit on my cylinder, make a gasket because the one they sent was not usable since it didn't fit my cylinder, buy a replacement cooling shroud without the scoop so the carb would fit, drill new mounting holes for the cooling shroud, replace the inner throttle cable, etc. etc.

Anyways, I have everything together and I've got a couple questions.

The main one is that the throttle doesn't return automatically anymore. Prior to replacing the carb and inner cable it returned freely just fine. I had to replace the inner cable though and it moves freely within the outer cable. When the cable is disconnected from the throttle at the handlebar and you pull it manually it returns freely, but when you connect it to the throttle and twist the throttle it does not return automatically. So it seems like the new carb doesn't have a strong enough spring to pull the throttle back closed... or something.

Are there any fixes for this?

Carb looks pretty good at least.

Does this work?

https://scooterlab.uk/product/jpp-lambretta-throttle-return-spring/

FWIW, my mostly original 65 Li125 Special is the same way--I have to intentionally close the throttle.

I asked the local Lambretta guru about it, and he said that's the way it was when they were new. It's the only motorcycle I've ever ridden that is like that.

Vespa's were the same way, even had an extra part in the headset to help hold the throttle open. mid/late 70's brought regulations in the US that it MUST close on it's own.

the Tommaselli Super Pratic B Throttle used on most Italian bikes of the time had a thumb screw that could adjust the resistance.

no no, we just call that Italian cruise control!

it shuts off on its own, the vibration from the motor is the control module.

For any sort of custom throttle cables I just head over to a bicycle shop and use shifter cables. They can't be beat for a smooth throttle action. Plus the bike cables are fairly inexpensive.

Weak return spring mechanism?

Hi

My advice would be, make sure your outer cable is routed correctly, the return spring in the 25's is totally fine.

MB sell a return spring for the handle bar end, these old Lambretta certainly have their own idiosyncrasies.

Sounds like a lot of work just to fit a carb.

Good luck.

Cgt75b.

https://www.lambrettaspares.com/spares/headset-spares/lambretta-headset-(handlebar)-rod-throttle-return-spring-mb/mrb0882.html

I have always thought it is too maintain speed while the right hand is off the gas while you use the right hand to signal for a right turn, hence no indicator lights on old models. The PX150E I have has indicators and does not have that funny clip to seize the accelerator tube. This would, however, only apply in countries that drive on the left. In the US, it wouldn't apply. This is all speculation. Maybe it is Italian cruise control.

So how is that lammy running?

Take headset cover off and see if it returns then. My GP200 did the same. The cable was getting pinched between the bottom casting web and top. I ground down the area and it allowed the cable to move free.