If it’s really “40-to-2-metres” then, unless it has links/switches/traps/whatever, it’s not resonant on most of those bands, and therefore it’s assuming some sort of ATU’s in use(*). Even when using an ATU a resonant antennna will have advantages. As you don’t have an ATU, your first step should be to make yourself a resonant antenna. That will be for just one band unless you use links or traps, of course, but a linked dipole isn’t hard to make. Plenty of instructions about on how to do that, and a handy calculator on SOTAMaps under extras. If you don’t have the bits in your junk box and need a starter, SOTABeams sell a kit of bits for making a linked dipole to which you will need to add a feeder cable and antenna wire of some sort. An antenna analyser is a handy help, too, as it’ll do a rather better job of measuring SWR than the 817/8.
Another monoband alternative is a simple vertical, but that’s not really practical for 40 metres, and even for 20 metres you’ll need a pole quite a bit longer than 4 metres. Again, you’ll find instructions around and about, including more than one place in this reflector (Lightweight Vertical Antennas, for instance).
I could rabbit on for hours, but that’s enough for now. Good luck. 
(*) Colin @G8TMV pointed out to me else-Net that it might be using the “Clansman” technique of expecting the operator to only un-wind enough wire for the band desired, which leaves the rest of the wire in a big (lossy) lump of a coil at the end…