MSR Firefly

Ok. I have a stove problem that has me stumped. I have an MSR Firefly. I have been burning mostly diesel fuel in it since that is consistently easier to find especially out of the country. Anyone who burns diesel in their stove knows well how dirty it is but I am not sure whether that is part of the problem or not.
The stove seems to preheat ok...I am able to get priming fuel into the cup and lit. But then as I turn up the gas after it is warm it seems to spit and cough and never gets a good flame going. I have cleaned the jet, the flame adjuster, and done the fuel line cleaning and nothing seems to have worked. However, I did notice during the fuel line cleaning that with the flame adjuster wide open it seems to cough and spit fuel like it had when I actually had a flame going. It is almost like it is intermittently sucking air rather than fuel out of the bottle. The bottle I am using is approximately 1/3 full or so so I wouldn't think that would really be the problem but I have to say that is what it looked like. Any ideas?

Here are some FAQs from MSR's website in this list that deal with various problems with MSR stoves. I assume the Firefly is an old model, but some of their tips might apply. If you don't see an answer there, I would call MSR and ask them. They have very good customer service.
MSR customer support

You might want to also look at the pump. First, I would take it apart and replace all the O-rings using the MSR Annual Maintenance Kit ($9.95). This is always a good exercise and will help you learn more about your stove. If you have questions, the MSR website can help.

The best thing would be replacing your current pump with a new Standard Pump ($34.95) released a couple of years ago. This will significantly improve the performance, even if your FireFly was doing ok already.

If all else fails, I would second TomD's suggestion of calling MSR directly. They will know what to do. I've personally seen the parts department and if your stove is in need of parts that have failed, they'll have them.