RE: Saito 125 no compression
Yes the exaust valve gets carbon deposits and sticks.
You need to take out the cilinder and take notes of all parts and position. Release the valve retaining ring and push valve inside cilinder being carefull not to scratch iside wall. Since it has carbon depisits probably wont like to come offf.
Once you have the valve outside use the dremel tool with the wire brush accesory to eliminate all carbon deposits. Be carefull with the part of the valve that seals with cilinder. Assemble your engine and should be great again. That is why they recomend sintetic oil only in your glow gas for this engines.
Cheers
Juan