Originally Posted by Valleyrider
Not going to get in a pissing match here. That being said, there are "If's" and "May's" in your advice given here. We all know that diagnostics online fall short of hands on first hand experience.
The suggestions that Scootern29, Buls4evr and I have made are based on our experience with 2 stroke motors. You bring up some good points and testing procedures, but a 40 year old TC/TS100 could use a little freshening up with new seals. If they aren't leaking when tested today, they surely will be leaking in the near future given the properties of todays gas....
Unless you have a strong desire to waste time and money, there is no real need to replace crank seals which are perfectly serviceable, in the hope of curing a problem which in many cases will not be related to crank seals at all.
Its very easy to test crank seals, and it will take maybe an hour to put together a cheap home made pressure tester set up, which in many cases will confirm that the seals are good.
First thing to check on bikes which have been standing for some while and have a good spark and compression is the carb. Again very easy to do this.......... simply remove the air cleaner hose, squirt aerosol brake or carb cleaner into the carb mouth, and see if the bike starts.
If it does start it will obviously only run momentarily, but this will confirm 100% the problem is with the carb, and has nothing to do with seals or anything else suggested by the net based experts.