Have a friend with a 2003 Fuel Injected FatBoy (roughly 30,000 miles). No engine mods other than exhaust, air cleaner and stage 1 download.

He says that the bike runs great on a full tank of gas, but starts to sputter and has even stalled out once that tank is half empty.

Does this sound like vapor lock or is it a clogged filter somewhere? I told him that I believe it to be vapor lock because the symptons only occur after the gas tank has been sealed up for a while. Any suggestions?

 

I have another friend who is certain that the filter and pick up line on the Electric Fuel Pump under the console both need to be replaced. He says that vapor lock is not something that is typically experienced on V twins.

 

yes need to check for a rotted hose in the tank some times they get pin holes in them and do not keep the pressure once the gas goes below the pin hole.
pull the tank drain the gas and just replace the lines

 

I know in the past when this has happened to friends of mine they had put the wrong aftermarket gas caps on or switched them I can't remember exactly what the deal was but it was venting related.

 

that was on the older bikes the twin cam has a vent up front of the tank. what happens is the pick up lines get little holes in them when the tank isfull there is no place for the gas to gosort of pressurises the whole tank . the vent will let it out slowly and it does not seem to be an issue as the gas gets used its like having a leak in a garden hose the gas(enuff gas) does not make it to the inj (with enuff pressure).
easy fix but a pain as you have to pull the whole pump assembly. you can do it with the tank on the bike tho just drain the gas

 

to check for vapor lock,just put cap on lightly and ride.If it runs right thats it.Get a new cap that is vented.
My 86 flht did the same thing untill I found the problem.