Hi Rob,
The ST.35 whas been a favorite of mine since the '60s. I still have 7 or 8 ready-to-go.

Fuel kind of depends on just which ST.35 you have, but in either case, the "Cool Power" blends you mention will not be adequate. The technology of these engines is the old Iron Piston running in a Steel Sleeve, and therefore require much more oil, at least 25%, during break-in, at least.

As far as which ST.35 you have, look at the Bypass side of the engine. If it says G21, you have the twin-ball-bearing version, and you can safely reduce the oil content to about 20% after break-in. If it has a "C" on the bypass side of the case, you have the plain (bushed) bearing version, and should stay with 25% total oil forever. Add about 4 ounces of Castor Oil to a quart of the 10% "Cool Power" for break-in, and don't ever let the engine go lean! A better blend is Powermaster GMA 10/22, in which is  Castor Oil is half the total oil. This is important for cooling, especially during break-in.

One "interesting" characteristic of the plain-bearing version is a tendency to start on just a prime; no battery hook-up. Very surprising, at  the least!

Break-in shoukd be with a wood 9-4 prop, and keep the engine on the edge of a 4-cycle/2-cycle run. Run for one minute and let it cool for 5 minutes. Do this 5 times. Then run for 2 minutes, cool for 5 mnutes. Do this 10 times. Then you can start running a full 2-cycle, always monitoring the head temperature. (If you can hold the head for an honest "One thousand-one, it's not overheating.) FOr the plain-bearing version, you should also monitor the case temperature on the bottom, under the venturi.

Venturis and NVAs are available, but may require some searching. Several folks make custom venturis.

Good luck,

Really the old C supertiger had several different P/L sets over its lifetime There was the baffled piston set, The original flat topped piston with little or no blowdown on the sleeve, a flat topped piston and a higher exhaust timing on the sleeve, and at the end of its production life the liner had perry porting.

"One "interesting" characteristic of the plain-bearing version is a tendency to start on just a prime; no battery hook-up. Very surprising, at  the least!"

Hmmm...never heard of this before....can you shed a little light on how this occurs....No battery and it runs on a prime....

Inquiring minds want to know.....

thanks....

the darn things would start without connecting the battery. This was quite startling! It ws not consistent, but it happened frequently enough that it kept us on our toes.

Possibly evidence of the oft quoted catalytic interaction between methanol and platinum.