St2300 - easily one of the most powerful/light engines ever done-
Here is what happened :
ST released the first version with a very large , conventional carburetor.
I got one of the first.
It was obvious that the carb would not draw fuel properly the way it was configured.
Why? The design changes mixture as the barrel rotatesand this "relative fuel to air mix" was excellent when the barrel was almost closed and the engine was sucking hard on the spray bar as well as the air thru the carb air supply.
as the engine reached full opening, the fuel "suction" really got diminished.
way too much air for the fuel available.
Just not enough suction from the crankcase at wide open throttle and lower (8000) rpm's.
Super Tigre intended there to be pressure from the tank - and on the FIRST production run - the single outlet muffler would provide fair pressure - about 1/4 lb.( I measure tank pressures with a quality 0-5 lb gauge).
The next production engines had a *******ized carb with a tiny bore in the bottom half and a reworked throttle opening control slot. Worse yet -a dual outlet muffler - !
This combo effectively killed any tank pressure and wrecked the air/fuel mix.
How /who/why this was done is a mystery still - My best guess is that they were trying to get more rpm with the dual outlet muffler and the carb redesign - well, that was simply an error.
Many users wanted an in cowl muffler - none of these provided correct tank perssure. the best I ever saw was under 1/4 lb with one stack closed off.
Pumps/regs were added by many with results from awful to ok.
The real fix -was to duplicate the first muffler and carb (for an engine running smaller props such as a 15x8) which worked fine on faster revving setups.
For real power tho - on props such as 18x8 which would turn over 9000 rpm, the setup was a F glow plug -25% nitro and oil,the original carb setup -(or a laterone redone to original specs and MOST important - a header and tuned can which brought up pressure from zero at low speeds to over 1/2 lb -up to 3/4 lb at full rpm.
The pumped setups I saw ALL, (thats's ALL), had so/so transition at lower speeds unless the top speed was still on the lean side.
The net result - premature ring wear.
I sold all my ST stuff and went to the ZDZ40 for the power I was after for 1100-1200 sq in models.
I also got tired of pouring a a gallon of 15 buck fuel thru in a single day.
But if glow fuel were a couple of bucks a gallon - I would have kept the Tigres.