Hi Andrew,
I agree with the other posts. One thing I have come across, if by chance your quantum is ohv ( which normally they are not) on ohv Briggs the spark plug gap is vital for easy starting. I had several 6hp ohv engines on Stiga compact ride-ons , which would not start with the key but with the rope. After many hours of stuffing around it came down to a 20 thou gap on the spark plug (which is in the workshop manual) solved the problem.
