HELP needed
 

I have been planning a trip from Manchester UK to Singapore for a few months and had settled on a 3/4 month trip riding a 125cc Honda ANF or something very similar. I was going to attempt to sneak into China on such a small inconspicuous bike I thought it may be possible if not the plan was to join a group at the last minute courtesy of VISA and sort out the extra cost on my return, however after a three day wet windy cold trip up to Scotland on which any pretence of camping went right out of the window and Travelodge became the chosen rest point I realised that I am too old unfit and dare I say it spoilt to successfully ride across Europe and Asia on a small motorcycle on such a tight timeframe, (it took me 3 days in bed to recover and a further 3 days to be able to stand up straight) So the plan has changed somewhat and although not cancelled is now completely different I really want to do this before I can't.
Does this sound feasible? Buy a reliant Robin (google reliant robin I always wanted one and they look like an ideal alternative with just about enough room for all my gear and a sleeping bag in the back) and set off early April spend a month getting to Ulaanbaatar this is where the changes have to kick in and help is needed option 1.
leave the Robin jump on a train to Beijing another down to Kunming alltogether spend 10 days crossing China, then over the border to Laos on to Thailand by train to Bangkok where I can buy a Honda Wave and ride it all the way down to Singapore at a nice leisurely pace taking 10-14 days Doable?
2. Postpone AGAIN try to get fitter and healthier save the extra money to drive through China? (Time is not my friend it goes too quick)
What I really want to know is can I leave a 3 wheeler somewhere in Ulaanbaatar for up to 2 months where it will be safe? Is there anywhere there that I could leave it and have it serviced whilst I am away? and is there any different rules for driving an 850cc three wheeler through China is it cheaper? (wishful thinking)
Either way the second week in April will be here before I know it and I WILL be setting off in a Reliant Robin for Singapore how far I get remains to be seen but as I have learnt through life experiences its the journey that counts not the destination so I fully intend to enjoy it more than I will be forced to endure it.
thank you in advance for any helpful comments also any groups planning to cross China to Laos either from Mongolia or Kyrgyzstan at the end of April mid May feel free to contact me with your crossing dates costs etc as if the costs are not too prohibitive I may well join you for that part of my adventure.
Keep Upright Billy