A few weeks back I was in lane 2 on the M4. Lost all power (after 35mins) pushed it into Slouf, shoved it in the back of my daughters car and got it home and open on the bench again. Bright white plug (that's new) 4 corners of piston seizure. It's started rubbish and ran iffy for two years. So new PM PROX piston base gasket and a hone is in the post. Don't know how i'm going to stop this happening again, been asking around for years about getting it running right, think I might sell and go back to a boring Leader. Too much conflicting advice: some say I wasn't running enough oil, some say I running too much and making it weaker. A shop says I shouldn't be running a runner ignition on a typh engine and it was too advanced. Some say they should only be run on 98RON. I couldn't find a dyno for toffee and found it impossible to test every condition. The last thing i was asking advice about was when holding a speed i.e. 60 mph the throttle is on the verge of closed and the engine doesn't know whether or not to accel or decel. Spec 172cc Typhoon 180 gearbox full circle crank runner red ignition 25mm delly ET2 airbox Standard exhaust 100 main 52 pilot 100ml: 5ltrs SIP oil Not thrashed everywhere, it's in a Vespa built for touring.
Get rid of the red cdi, that is the major reason , As someone told you, it's too advanced for an air cooled engine. I'd go up on the main jet a little as well using a 25mm! 2% premix. I personally like the std carb jetted upto 90-92, they work so well and not far off a 25mm for performance.
A water cooled engine has a very stable "thermal stability" meaning machining tolerances are better, engine temp is a constant in all weather conditions. An advanced ignition timing creates high temps in the cylinder, air cooling can't cope. The higher the ambient temp the worse an air cooled engine will run, it can't cool itself. There is a post on this forum about such issues, the stock cdi is perfect.
Do you think a 25mm might be too big for standard air box/ exhaust? I’ve wondered that for a while. Feels like it. I might try a standard carb again. The return of the auto choke would be welcome.
It's a bit overkill with std pipe, there is std carbs on ebay, the Mikuni carb is lovely, just jet it up on the main!
