A few weeks ago I got thinking about this. My 'Wing is now pulling a sidecar (= burning about 20% more fuel) and the pump is drawing from the Rotopax mounted on the side of the sidecar by the saddlebag about 40% of the time (significantly farther away from the pump than the bike's tank and lower so it won't syphon if the pump dies). I figured it was about time I did something to make sure I didn't end up stranded by a dead fuel pump so I started searching eBay for a fuel pump diaphragm that might be useful (or a kit that contains one).
I found several that looked promising but the only one that had a diaphragm that was usable was a kit made for a 1929-1933 Chevy offered by a seller called Marxparts. The listing said "This is a Fuel Pump Gasket Set and Diaphragm for a 1929-33 Chevy fuel pump. It includes modern neoprene diaphragm that handles today's fuel types, 3 bolt spring cover gasket, glass fuel bowl mounting gasket, and fuel pump engine mounting gasket" I contacted him to ask about the dimensions of the diaphragm and told him what I wanted it for. He told me that the diaphragm is 3 1/4" (approx. 82.5mm) diameter with 3/16" holes. The measurement from the inside of one hole to the inside of the opposite hole is 2 1/2" (approx. 63mm). He also told me that they sell the diaphragm separately for $6 + shipping ($4 to Canada).
The diaphragm for a GL1000/1100 pump is 68mm diameter and the clamping diameter is 45mm so I ordered one.
I finally got time to mess around with it today. I did everything pretty much the way Peteybug described except for a couple of things:
- I took the pump apart to work on it. Instead of drilling the ball bearings out with a carbide bit as has been described in another thread, I drilled a couple of small holes just inboard of the balls and at an angle and drove them out with a small drift. This allowed me to clamp the shaft in my drill vise for drilling &c.
- I held the top of the pump against the new diaphragm, centred it by eye (the original holes will be a bit less than half exposed) and marked the new holes and the outside diameter with a ball point pen, then punched the holes with a leather punch and cut away the excess with sharp scissors.
Now I need to get time to mount it on the bike and try it. I will probably carry my old but known good pump with me for a while just in case.
I will report back after I have had it on the bike for a couple of weeks.
If you want to order one of these diaphragms, go to http://www.marxparts.com/repro%20chevy_fuel.htm
(last item on the page) or email firstname.lastname@example.org
and tell him you want a 3/1/4" fuel pump diaphragm like he sold Sidecar Bob