Piaggio sfera / zip 1 runs better cold
 

Hello,
this is the same scooter from the previous thread, where I solved the problem with my CVT tuning. It accelerates nice and tops out at 63kph (I traded top speed for acceleration as I am using 3,25g roller weights).
Now the problem is that it goes well on quick spin, but as it starts warming up it goes less and less.
It`s stock, except for lighter roller weights, PHBG 19mm carb and airbox from lawn mower (I changed it because it goes better with it than with free flow filter) and exhaust from Chinese minareli scooter.
I am running it with #75 main jet. If I upjet or downjet it`s just worse.
Spark plug is brown.
It`s not bogging, it just looses power and top speed.
Here is the graph from speedview app.
Attachment 986

I had a scooter that when it got hot the transmission would get wonky. I replaced the torque spring with a slightly stiffer one and put in a new belt and that solved the problem. Now, with yours I dont really know where to start. I'm "thinking" a stator issue for some reason.... I had a Genuine Buddy 125 that when it got up to operating temp the stator would break-up and rob the scoot of power. Volt meter helped solve that annoying issue! Is it sounding smooth when it looses power? Does it still rev-up correct and just not respond snappy? Do the revs drop as it looses power? Need a bit more detailed symptoms so we can hopefully solve this.

Hello, thank you for reply.
It doesent feel like electrycal problem. The case is that it will not loose power or drop revs until I left throttle and back of the top speed for the first time.
I think that I will have to replace torque spring too, my previous problem was that top speed would drop alot even at slight wind or uphill, than I installed hard rubber ring (thermal resistant) under the spring.

Just out of curiosity, how many miles (or kilometers) are on this scooter? I assume you picked it up used and are just trying to get the most out of it, and there is nothing wrong with that. Its rare that anything wears out on a normal owned 50cc but some people (me!) pound the miles on, and tend to abuse them also. Burnouts are the worst thing for a CVT driven scooter! So if the prior owner was hard on it and/or the miles are kinda high you might need to do a transmission overhaul. Measure the belt width against the service manual spec. All that being said try a stiffer torque spring. Malossi white is a good start. Malossi may say white is soft but its stiffer than a stock spring.

Hello,
yes, this scooter is from 1992 so it has long history. Belt was worn for 3mm, so I repleaced it with new one.
I got this scooter for two crates of beer from a local hehe.
It camed with new tyres, new piston and dellorto phbg 19mm carb and the clutch also looks like new.
It`s and old ugly (at least to me, but I have seen worse) scooter, but I like it because of it`s quality and it`s Piaggio engine.
It has 11k kilometers.

Im planing to register it and install 70cc bbk, but I wont do any of this until I get it running good.

2 stroke tuning can be both fun and frustrating! Now, did it run normal at one point, or did it come to you with running issues? I do agree that it needs to be ironed out before going any further, as a bbk kit has is own joys for tuning correctly. Dont get discouraged as the rewards are worth the time and effort involved. Im currently overhauling a 98 pre-bug Zuma (aka BW's) and Im not really sure what route I want to go. But it needs to get running safe and reliable before anything is decided. Curious again, are you in the states or overseas? 2 stroke Piaggio's are rare in the US but you can still find tons of tuning stuff for them.

It came with running issues, owner said that it was because of too big carb.
It was bogging realy bad and belt was worn so it was overreving and doing top 40kmh afte tuning the carb.
After chaning the belt it started to act much different, I had to change 5,2g roller weights to 3,25g because it was driving way under it`s powerband.
I`m from Europe, Slovenia, just next to Italy so we have alot of Piaggios on our roads.