Woah!!!
May I ask whether an engineer (for haven's sake tell us you're not a pilot) thinks this is the right place to be asking such questions. No doubt you have problems operating in Zim but this is a matter for Allison or your C20 support organisation, not unattributable opinion on the net!
fails to light off on first start at 15%, but will light at 8-10%
How the **** would you know that????
The flight manual clearly states "A start should not be attempted with N1 below 12%"
Do you mean to say you tried this????
after light off will quit at +/- 40% and throttle needs to be open wide to keep start going
Open wide at 40%?
You've tried this too? Bejasus! Give us a clue on the TOT you saw or couldn't you bear to look? The results if the thing suddenly started operating correctly at that point with the throttle full open don't bear thinking about.
My opinion, purely surmise you understand, is that if the exhaust doesn't smell of roasted Troll then your hot section probably resembles the cheese on top of a pizza. And that smells like burning paper. ie a small mountain of $100 bills...