Posted Monday, February 27, 2012 @ 09:16 PM
Great new hangar!
I'm not sure that vaporisation depends on octane rating. Vaporisation depends upon volatility, which is somewhat different, although motor fuel (Mogas) is generally a bit more volatile than Avgas
Octane rating is all about pre-ignition, and varies with compression ratio.
The original 1200cc Rectimos only had a 7 to 1 compression ratio, so 80 octane fuel was fine.
If you're now running 1400cc cylinders & pistons, your compression ratio will be around 8.2 to 1, so you should be using a higher octane fuel.
I normally use approximately 3 parts of 91 RON auto gas (the lowest octane available on the forecourt here) mixed with one part of Avgas. I am told that 100LL Avgas has around twenty times the amount of lead in it that leaded auto fuel had, so I guess that will be more than enough to delay pre-ignition (knocking, pinking or pinging).
You may remember that, when flying solo, I time my climb for the first couple of minutes after take-off to ensure my enigne is performing adequately. Over the years, I have noticed that if I am using more than my usual amount of Mogas (too little Avgas) the climb rate becomes less. I can't hear any pinging, pinking or knocking, but the performance definitely drops off, so recently I've tended to err on having too much Avgas rather than too little.
I know none of this addresses your fuel vaporisation problem, but it should be of general interest.
Of course your vapour lock problem will go away immediately if you use a standard carburettor.
To be honest, with no fuel pump and no flop-tube tank pick-up, I really don't see the point of having a slide injection/carburettor with no float bowl, particularly when there is such a strong reason for not having it.