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• The stock pump has 4 connection points: feed (from the oil tank), return (to the oil tank), out ( to the oil filter) and in (from the oil filter). ²⁾ The oil pump acts as a pass through for the filter return line. ³⁾
• Since XL motors just flood the motor with oil, the issue is on the scavenging side (trying to get the oil back out of the motor) hence the trend toward bigger scavenging sections and smaller pressure sections. Many racers actually reduce their oil pressure trying to solve scavenge issues. The last thing in the world you want to do is pump more oil into an XL engine. ⁴⁾
• The line returning from the oil filter pad feeds oil into the bottom of the cam box, where it then goes up through the cover, oiling the pinion and lower end, as well as going up to the lifters and valvetrain. ⁵⁾

• The oiling system changes that came with the introduction of rubber mounts were a huge step backwards.
• There are a lot fewer problems with the 2008 and later bikes judging from previous years as they have they updated rocker boxes and breathers. The oil pump is not the end all fix though. On the 06 and Earlier bikes just changing the oil pump was not the step that suddenly made the blow-by disappear. Neither was correcting the ring end gap. ⁶⁾
• You know what's ironic? The better the ring seal, the worse the problems with XL oiling are. A little crankcase pressure actually helps the scavenging. We saw it a LOT when using gapless rings. It just plays hell with the oiling. ⁷⁾
• The 07 and up style pumps are a great upgrade to an 86-90 engine. They made the scavenge section bigger and the pressure section smaller. ⁸⁾

* The 5-speed to 4-speed conversion is not a hard mod to accomplish. However, I would not put it on hoping it'll solve a wet sumping issue. Wet sumping is more of a crankcase pressure issue in my experience. I've never had any luck curing a wet sumping issue by changing the pump. ((aswracing http://xlforum.net/vbportal/forums/showthread.php?t=1589124))

Specifically, the 2007 Buell and XL style oil pumps have the bigger and better scavenge gerotors. It gets a little tight right there where the line from the oil filter pad feeds into the bottom of the cases (between the return line fitting on the pump and the feed line into the motor) as the pump tries to hit the return line fitting on the pump (the feed line into the motor will normally be coming from the oil filter pad). That's the only tight spot, the newer oil pump bolts right up otherwise. But, with a little grinding, it can be done. ⁹⁾

• When you take off the stock pump, it will expose a 1/8“ hole in the bottom of the gear case. The 07 style pump doesn’t cover the hole ¹⁰⁾
• You'll have to put a 90 degree fitting in it, before you put the 5 speed pump on. This will allow you to hook up the filter return line and give you oil pressure.
• You may have to tap the hole for the 1/8-27 90 degree fitting. ¹¹⁾

• The pump was made longer and the screws made longer to match it (in 1998) with the big oiling system change that isolated the gear case drain from the crankcase and added a scavenge inlet in the gear case. This change applied to both Sportsters and Buells, though there's no difference between the two. The part number for the screws on a 2007 Buell and 2003 Sportster are # 4765 ^{12) 13)}