Strange fuel pump return line issue

jsedacca

Just finished up replacing the fuel pump in my 851 alloy tank with a similar 52mm pump from motoelectrics (BMW style pump). After reconnecting all the lines, the bike primed and fired right up. Just by chance, I had the return line disconnected (installed quick disconnects for easy tank removal). Bike idled great, revved up freely and sounded perfect. Once I reconnected the quick disconnects for the fuel return, the bike slowly dropped RPMs, sounded rough when tried to rev (could see a slight backfire in vert cyl) and would ultimately stop running. I've popped the tank off to check everything and it's like it was before the fuel pump change. Wondering if anyone has had a similar problem with the return fuel line making the bike run rough. Thanks guys

Jared

Jasper

Have you got the right size QD,s? Sounds like you are starving it of fuel. So, either too small or not connecting properly.

I have fitted some to my SP5 while i get my Corsa tank sorted.

Weed

Check your fuel pressure regulator. The return line manages the fuel overflow from the regulator. With the return line disconnected you will be getting the full fuel pump pressure to the injectors

jsedacca

I have the same QDs as you Jasper. Just to make sure the fuel pressure reg is plumbed correctly, after the injectors, the hose goes to the 'bottom (vertical) barb of the regulator. The other hose connects to the horizontal barb on the regulator (faces right side of bike) and back to the return valve on the tank.

What should I be looking for with the regulator?

jsedacca

I replaced the return line with a hose WITHOUT the quick disconnects and it did not resolve the issue. After more digging around, I swapped the hoses going into the regulator and the bike fires up, and idles rock solid at 1200rpm. Revs freely and and has no stutter. Here's the kicker, it was plumbed INCORRECTLY when I purchased the bike. Hopefully this resolves the fueling issue I've been having since buying the bike. Time to get some tires mounted and take it for a ride. Thanks for all the help guys

Jared

Jasper

Glad you sorted it mate. Sorry I didn't get chance to reply before you worked it out!

marvin

jsedacca wroteI replaced the return line with a hose WITHOUT the quick disconnects and it did not resolve the issue. After more digging around, I swapped the hoses going into the regulator and the bike fires up, and idles rock solid at 1200rpm. Revs freely and and has no stutter. Here’s the kicker, it was plumbed INCORRECTLY when I purchased the bike. Hopefully this resolves the fueling issue I’ve been having since buying the bike. Time to get some tires mounted and take it for a ride. Thanks for all the help guys Jared

That's strange ! I have ridden with Donnie ,on that bike, many times and it always seemed to run just fine. I rode with him this weekend and he said "What fueling issues"? Are you sure you didn't just screw up and are now trying to blame it on esomeone else?

jsedacca

marvin wroteThat's strange ! I have ridden with Donnie ,on that bike, many times and it always seemed to run just fine. I rode with him this weekend and he said "What fueling issues"? Are you sure you didn't just screw up and are now trying to blame it on esomeone else?

Just seeing this but to clarify, this is for my 91 851 I picked up which was a bit of a basket case to begin with. The 888 from Donnie is almost complete it's restoration. Just picked up the bodywork from the painter the other day.