5:28 p.m. on October 27, 2006 (EDT)
Steve -
Your Primus is a 71L. I have one as well, of similar era.
Anyway, from your description, your Primus and Whisperlite both are in serious need of maintenance. If the Whisperlite takes longer than 3m30s to boil a liter of water, it needs cleaning of both the fuel line and the jet. The jet is best cleaned by removing it. The needle cleaning tool used from the outside just pushes the accumulated carbon back into the fuel line, where it will come back to clog the jet. Also, doing it that way enlarges the jet over time (same with the 71L), which sooner or later will require replacement. That's why MSR went to their "shaker jet". It also sounds like you need to learn how to properly prime both the 71L and the Whisperlite (don't worry - 90 percent or more of users of liquid fuel stoves have no idea how to properly prime them. If you have a priming flame more than 3 inches high or can't get it lit on the first try at any temperature above -20F, you aren't using the right technique).
The full cleaning procedure for the Whisperlite is as follows:
Undo the nut on the bottom of the burner assembly and remove the hose and jet assembly.
Using a phillips screwdriver, undo the burner plate assembly, clean the carbon deposits between the plates, and reassemble.
Remove the jet from the fuel line assembly, clean it and set it aside (those with shaker jets, don't lose the tiny needle "thingy", and don't bend the needle - and remember it goes back in with the needle pointing up toward the jet).
Next, pull the cable out of the fuel line. If the stove is regularly cleaned, you can use the MSR multi-tool by inserting the end of the cable through the hole in the multitool that is just larger than the cable diameter, twisting sideways and tugging. If that doesn't do it, then get some needle-nose pliers, maybe with the help of a bench vise. If that still doesn't do it, soak the inside of the hose overnight in a solvent like mineral spirits (which means you have superserious clogging). After you get the cable out, clean it with a solvent like mineral spirits (don't use white gas, even outdoors with lots of ventilation - white gas is too explosive if there is any flame or spark anywhere close, beside which mineral spirits just works better). You may need to use a wire brush to get the dark stuff cleaned completely off. For the fuel line itself, run some of the cleaner through the hose, then use the cable like a pipe cleaner, running it back and forth in the fuel like. Again rinse with the mineral spirits.
When the cable is dry, look at the ends. Often the end that was at the jet has a ball of solder. This will also block fuel flow. Use a file to file the solder ball down to the same diameter as the cable. Be sure to clean off all filings.
When all is dry, put the cable back into the fuel line, making sure you get it all the way in (it is sometimes hard to get around the bend in the line. With a full fuel bottle with the pump in place, attach the fuel line to the pump, and pump up pressure as if you were going to cook. Outside, in plenty of ventilation, run about a cup of new, fresh, clean fuel through the line (catch it in a can and dispose of it properly). This does a final rinse of the fuel system.
Finally, reassemble the jet (don't forget the shaker needle, if you have the shaker jet type), making sure you put the correct jet in place (white gas and kerosene jets are different diameter openings if you have the international version). Then reassemble the full burner assembly.
Once everything is back together properly, fire it up. You should have a better performing stove now. Oh, yeah, did you replace the O-rings and little ball in the pump recently? If not, these lose pressure from the fuel bottle, and thus lose performance.
It isn't really hard to do this, even in the field. Other liquid fuel stoves are very similar in their maintenance needs.