Well, I thought I would share my knowledge and (excellent) results of fitting the newer style small fuel pump to the earlier 851's (91-) which used the big fuel pumps. I started off by buying a Walbro GSS342 high pressure pump. There are essentially 3 pumps you can buy: GSS342, GSS341, and GSS340, the difference being only the inlet offset. There is a new pump you can use F20000169 but you just have to make sure you space it in the mount for filter clearance. You may opt to buy a copy version but you get what you pay for. So, now that I had the pump I needed the plug and a way to fit it in the existing mount. I found what I needed on APE site. You can buy the pumps from them also, but I found a new one on Ebay for cheap. You don't need but I recommend buying the 12" pigtail harness, makes wiring a breeze (you take your chances fitting your own terminals to the pump). Also, you will need to get a sleeve so that the pump fits nicely into the standard mount. They have three sizes, you want the largest being the 55mm. I did buy a filter for the said pump, but realized that there was no feasible way to fit it in the tank which is why I went with the sleeve and the standard filter. Speaking of the standard filter (I'm talking the pump filter, not fuel filter) a direct swap for the Ducati part is BMW 16 12 1 455 126 if you happen to have one laying around which I did.

As far as fitting the sleeve, you want the fuel pump inlet to protrude 30mm past the stock rubber mount. It's quite fun fitting the sleeve. It's a very tight fit trying to get the pump and sleeve into the stock mount but you will figure it out. Don't put any pressure on the pump's inlet of outlet or they will break off (especially the outlet nipple). Also, the pump comes with caps on the inlet and outlet; be sure to cut them off instead of trying to pull them off so you again don't damage anything. Back to the sleeve. Fit the sleeve of the pump completely, then after you get it seated where you want and in the stock plastic/rubber mount, cut the excess foam off where the pump filter connects to the rubber mount because you will never get the filter over the foam, trust me. But, leave the excess foam on the pump top just for protection.

Oh, one more thing, the pump I got has a small mount for the filter that goes with it (that you won't use), trim this white plastic piece down so it's even with the inlet. Otherwise it will contact the filter housing not allowing the inlet to be totally down.

Works like a charm!

Robert