I have an old ST3000 with a ST carb that has the oft-mentioned problem of loading up and dying at a specific spot in the midrange. I thought I'd try the fix mentioned in several threads of inserting a restrictor in the carb barrel and obtained part SUPG2420, then realized the particular carb in my engine has a smaller throat than the insert (11mm OD, 9mm ID). The throat diameter is only 8mm. Is this a carb from a smaller engine, say a G60? I did happen to have another restrictor, one for going from 8mm to 7mm, and thought I would try that. Or should I just replace the carb with an ASP 91 unit?

Have been running Omega 10% (17% oil; 70/30 synthetic/castor). The motor is well broken in and I'm ready to thin out the oil content - I figure a half-gallon of Omega and a quart of straight methanol will mix down to an 11% oil content. Would that have any effect on the midrange problem?

Appreciate insight from any and all quarters!
-RB8

You'll find that a fuel with 10%-12% oil content, all castor, will improve the engine's handling a LOT. Also, if you run 0%-5% nitro, it will also help. The engine was designed for low-oil, low-nitro fuels. Adding an O.S. Type F glow plug has also helped a lot of people.

Great! So I'll try the "thinnned out" fuel before inserting the smaller carb restrictor. Nitro is still a bit high at ~6.7%; maybe I'll get some castor from SIG and bring down the nitro below 5%.

I'm running the Hangar 9 4-stroke glow plug (3011), and since the rpm doesn't fall off when I remove the glow driver, I figure it'll do the job. My guess is they are about the same heat range as an OS F plug.