Originally Posted by bairdco
resurrecting this old thread because i've got the same problem 2door had.
switched my old motor from Valvoline 32:1 to opti2, and just couldn't get it to run right.
it had about 1000 miles on it, and would do an easy 35mph, good power all around, etc.
put the motor on my new build and put opti2 in it at 100:1, and the thing just wouldn't run right.
My theory: The piston/cylinder wall wear in the older “high mileage” engine is such that it needs the 32:1 mix of regular 2-cycle oil to seal the gap so you get enough compression for the engine to run (this is probably normal for an engine that lived on such oil). When you try to run the 100:1 mix of Opti in it, there isn’t enough oil in the mix to seal the gap so you don’t have enough compression for the engine to run. Opti oil lubricates differently and the piston/cylinder wall wear is different – it results in a gap with closer tolerance. An engine broken in with Opti will work fine, but if you switch to it in an engine with regular oil wear, there isn’t enough of an oil seal with the Opti to get the compression you need. This may show up if you do compression tests on the engine using the two different mixes. Another way to test would be to put the Opti mix in, but take out the spark plug and squirt a little 2-cycle oil into the cylinder (enough to coat the cylinder walls and piston) then start the engine. If it runs for a few seconds, then quits, it’s probably because the oil film wore off and you lost the compression.
Run the regular 2-cycle oil in the bike and enjoy it.
Why do I think the above? I read all the other posts on this site about Opti II, and read the stuff on the manufacturer’s web site so I know how the Opti II works. In addition, I had a relatively low-time 2-cycle leaf blower that I inadvertently put straight gas in to. It started right up and ran for about 5 min. then quit. I’m sure the piston walls were scored due to a lack of lubrication. It would not start unless I put a little oil in the cylinder. Then it would start, run fine for a few seconds and quit. Lesson learned.