Hmmm fuelling problems can be a pain in the ass to sort unless you have a really good idea of what is causing the issue. This is made a somewhat worse on the early bikes with a rather basic vacuum controlled fuel tap and a vacuum fuel pump of which only the pump is re-buildable).
So, firstly is it actually the pump you have replaced or the tap?
Secondly, are you saying you are running it without a fuel filter at all?
The filter really wants to be there as there isn't one in the tank (like the later bikes) and so any bit of grit getting into the diaphragms of the pumps will likely cause havoc and give further problems.
Personally I would be checking the easy things first such as the fuel tank breather pipe as it can clog at the tank end or at the 'exposed in the road crap' quite easily and this usually shows itself as a hissing sound when you open the fuel cap.
Next, make sure all the fuel and vacuum pipes are in good condition with no splits and not getting kinked under the tank.
But with the bike getting on for twenty years old (like mine) ideally I would be going through the whole lot and replacing everything along with giving the tank a good flush out.
Last year, I did just that and went through the entire fuel system of my 1997 90 replacing almost everything after experiencing what I believe was vapour lock (only ever showed up on hot days when in heavy traffic and at filtering speeds). I have never had carb icing cause any more problem than it running a bit rough and farting around and it only shows up once the motor is warmed up a bit say around five miles into a ride.
Some of the refresh I did can be found here:
http://www.ukmonster.co.uk/monster/s...hlight=refresh