Ok. I have a pretty decent amount of knowledge when it comes to these glo Engines. But I’m stumped. I have not pulled it and looked at piston and liner yet. My brothers engine. OS B21. I’ve reset the needles to drake carb settings. Idles on the high side. Runs great but when I let it sit for a bit to idle. It seems fine then draws down and dies. I’ve tried leaning and richening the low needle but no difference in response. I can easily run the fly wheel over compression stroke so doesn’t seem to have a great amount. Any ideas ?

High ide above factory setting is a worn piston/sleeve. All Os engine recommend 18% oil lube.

Is it? These race engines run normal race fuel and so run normally 9 to 12%, any higher is a loss in performance.
High idle and then drops can be a 2-stage idle where the idle is not set right for the 2nd stage., It can also be a bad or a too cold glowplug. And yeas, it can be a worn P/S set.

Os has always been 18% oil lube I will never run anything less as it will shorten engine life and have a smaller tuning window. The new manuals only say commercial fuel only.

Yeeeaaa, that's a hard doubt. Got a link to a manual that states that? I just went through all their discontinued .21 manuals and none of them even mentioned oil content.

Really, please tell me/us more about this...

I am going to get some popcorn

These aren't plane or heli engines. Please stop spreading incorrect information. When reading your posts on this and other threads, I get a very know-it-all vibe from you. However, if you can prove your statements, I'll happily sit back and admit fault myself.

15cv_series.pdf (os-engines.co.jp) Page 1. You didn't even look! LOL!

21rg_series.pdf (os-engines.co.jp) page 16 . Who's spreading incorrect information NOW!

Just in case you mess with the document?

Now show the oil advise B210x engines.

Car Engine (os-engines.co.jp) There is no B210X?

Oh man, how stupid you are. You know the x in 210x can also be a random number? It is a standard notation....
So like B2101, B2102, B2103

But your examples says enough about what you know, you are a basher and no racer, also your mentioned engines are older types.

Oh MAN how stupid are YOU really???. You don't give a specific engine model? So you get what you got. I showed you The proof that Os engines used 18% oil lube. Yet you continue to bash the truth. Who said anything about a basher or racer???? I didn't.. The manuals for the B201X? all show no oil lube content advise. Only say quality commercial fuel.

FYI the new Os site doesn't show all the discontinued engines like the old site did. I have engine's that are listed only in the timeline back to 1984 and Os doesn't have manuals listed anymore.