Hercules Supra 3D restoration

[mj]

My first-born son (aka the first two-wheeled motorized vehicle I've ever owned) has returned back home



I picked up my 1988 Hercules Supra 3D moped (49cc 2 kW / 2.7 HP two-stroke 3-gear manual transmission Sachs engine, type 505/3 DK) last thursday. It's been hidden away behind a shed exposed to all elements this planet has to offer since 2003. I cleaned it today (almost no rust on a 22 year old moped is what I call real good quality!), changed the spark plug and gear oil, haven't found an air filter yet so had to clean the original 1988 air filter. Four kicks later the engine started and runs pretty well once it's warm. Terrible when cold though - when it dies it's really hard to start again, and it sounds like it suffers from a really terrible cough. It gets better after the first hundred meters or so, although I had to readjust the clutch and throttle cable. I'm having trouble with 2nd gear which makes a really horrible clunking sound - my guess is that the gear wheel is loose on the drive shaft. I can maintain speed in 2nd gear but as soon as I accelerate it makes that sounds and doesn't get any faster at all. First and third gear work perfectly fine.

Anybody ever had one of those and know what the problem with the gearbox could be? Also, any ideas how I could improve its cold run? I'll replace the almost ancient air filter ASAP, still looking for a replacement. Spares are a bit hard to find since the engine and moped were only built for a few months in 1988. Any ideas what else besides replacing the 1994 tires I should do?