RE: Webra Speed 91 (old)
Mr Hughes,
Wanting to run all your glow engines on the same fuel, is akin to running your Chevy family 'beater', your Lamorghini Diabolo and your Ford PowerStroke™ Diesel truck on the same fuel...
Engines are never 'one size fits all'. Model engines cannot compromise with you.
Each needs at least a certain fuel specification.
Some may run better on a certain fuel, while other engines will not tolerate it...
FAI fuel with 5% nitro added will run very well in all your normal two-stroke engines.
Your YS four-stroke, on the other hand, will just puke on it... 20/20 synthetic is very good for it.
...Just a couple of examples...