In order that you have a better understanding of whats happening under these circumstances, click on the following "link". http://www.jag-rotax.com/ On the "Home" page click on "FR125 Max Engine" Then click on "Operators Manual" (PDF) Scroll down to page 94 entitled "9. Setting of the exhaust valve timing (only FR 125 MAX)" This paragraph when read in conjunction with the Performance Characteristis Graph will paint a clear picture of whats actually happening when the Exhaust Valve fails to open. ie. it will follow Performance Curve 1 (the dashed curve) as opposed to Performance Curve 2 (the solid curve) when it is fully open. Ideally the Exhaust Valve should open @ 7,500RPM. The Graph clearly illustrates the effect on "Performance" if the valve opens too early or late. I personally don't think it would matter which Carburettor you use in these circumstances as you will have less than 50% of the Peak Power available to you anyway. The Carburettor is selected to suit the Circuit, Driver style and Motor Performance!
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