When I visited Japan this year I bought a pack of Tachikawa (crowquill) nibs that came with reservoirs. I decided to use them to improve the Ackerman Pump pen that I had. The Crowquill pump pen comes with a white rod that you have to jam into the crowquill nib. Often times, it is very hard to remove, and damages the nib. I would also need to pump it often so that the ink would flow. It's good but I made it better.
1) I did away with the white rod altogether.
2) I just inserted the Tachikawa nib with the reservoir into the crowquill pump pen section. But it was loose.
3) So I cut up a q-tip, sliced it so it would flatten and broaden and stuffed it at the back of the nib. That made the nib fit into the section snugly. You could also try cutting a portion of the ackerman white feed or a straw to serve the same purpose.
4) Without the feed, the ink just falls down into the reservoir whenever you pump. You can see the ink collect in the reservoir. And once you use up the ink there, you just pump more ink into the reservoir. The flow is so much better this way. Perfect flow, I'd say. And you don't have to pump so often. Crowquill nibs give you very nice hairlines. Some are stiffer while some flex beautifully.
I tried this same principle on the G-nib Ackerman as well.
1) I did away with the G-nib Ackerman feed.
2) I used a piece of plastic cut from a tiny tooth brush holder.
3) Used a dremel to shave it down to the size more accurately. If you don't have a dremel, use sandpaper.
4) Cut a slit in plastic so ink will flow through the plastic and not around it. You can use woodcarving tools or anything sharp. I used a dremel. Be careful.
5) Insert a standard reservoir into the G-nib. (Reservoirs are available at Straits Art Co. if you live in Singapore.)
6) When you pump, the ink collects in the reservoir and you can write/draw until it empties. Then you just need to pump it again. The reservoir can hold a lot of ink. With this modification, you won't have to worry about the pen burping ink. A G-nib on an Ackerman is like using a wet noodle fountain pen!
Notes: 1) It's best to use fountain pen ink so you don't have to worry about ink drying up.
2) Use nibs that don't rust. I think the Zebra G-nib doesn't. But others might.