I don't have the answer aldot, but a 1.5 or 2 litre car starter motor draws around 150 amps. If you just scale that down in proportion to the engine capacity, you will probably be close. However a fuse in a starter circuit sounds likely to cause problems rather than solve them. It will cause a voltage drop, and applying low voltage to starter motors often results in them locking up rather than rotating the engine, then the starter motor and wiring both overheat. (Fuses are rated by their burn-out current, not voltage drop, and fuse blocks are even worse.)