I have a cheap Apollo brand bike which has very soft suspension and sometimes leaks brown rust coloured fluid if compressed hard enough. both sides have a plastic cap which prys open (not unscrewed) to come off. Is there anything I can do to make the suspension more stiff?
Cheap suspension forks just use a big undamped metal spring in each fork leg. If you can disassemble for the forks and don't mind making some irreversible modifications, you can increase the sprint rate at the expense of travel by cutting and shortening the springs. You would need to add spacers of the same length as the reduction in spring length. Sections of appropriate diameter thick wooden dowel would do.