The fuel tank on my 929 keeps building pressure and I can't figure out why? I've checked the vent lines by blowing through them and they're clear. It builds enough pressure when sitting in the sun, and i unlock the fuel cap it blows itself open and I can see the tank depressurize. Any ideas?
Would this pressurization cause the bike to have a "miss" when at operating temp and idleing? I initially thought it was bad plugs so I changed them, still does it.

 

is your bike a california model, with the purge solenoid and evap canister? (can may have been removed) the tank will have 4 lines: fuel pressure, fuel return, drain from the filler area, and the vapor vent (cali models). non cali models vent to the outside somewhere. i've only had cali models, so not 100% sure exactly where. if it is a cali set up, make sure the purge solenoid opens and closes with power and ground applied to the pins and that the canister isn't plugged up.

 

It's not a cali model, but it does have 4 lines that come out from the bottom of the fuel tank. I'll double check my manual and see if I can tell where the lines are routed.

 

1. Fuel tube
2. Fuel return tube
3. Over flow tube
3. Breather tube

 

Check th flow all th down thru th breather an over tube lines.