Fuel pump on a bike didn't originally come with one.

[jmiller416]

I am planning a little bit of a strange build here. Most likely a 70s CB550 four. But I am theorizing about building a custom tank that would be fitted under the seat. I would be using the Mikuni 14 litre per hour vacuum fuel pump. My question would have to be, will the float and needle valve be able to stop the flow of fuel into the bowls when they are filled to their normal level? Any thoughts or comments on this would be greatly appreciated.  

Edited November 3, 2015 by jmiller416

[doug the slug]

There usually is a difference in float valves when using a pump vs. gravity fed. On snowmobiles that use pumps, a mikuni carb has a needle & seat rated a lot different than a motorcycle one. You can look this up, but I recall the sled ones at one point something, while bikes are around 3 something (depending on the intended motor used I guess). Some older Honda quads used a fuel pump since their tanks were under the seat as well, but I'm not sure if the float valves were replaceable. I suppose this depends on what carbs you plan on using and if you can obtain the correct parts to match your setup. The joys of custom builds, huh?!

[jmiller416]

After doing a google search (as opposed to just searching forums I frequent) on this topic I found a go kart forum where people were talking about using a motorcycle engine on their karts, and needing a fuel pump to lift to the carb(s), a simple solution these folks came up with is a return line by just adding a 'Y' adapter in the fuel line to the carb, the trick would be to just have enough pressure at the needle seat to mimic a 1/2 to full tank of fuel without starving or flooding throughout the entire RPM range.