That Dubro seamless "neoprene" tubing is not good neoprene. I use it for a vent line on my tanks and thats about it. For my fuel line I used Viton (but am now out) or Nitrile.
I would only buy neoprene or nitrile lines from an automotive parts supplier.
The stuff the hobby shops sells is intended as a cheaper line for smoker systems.
Call up any automotive parts store and ask about fuel lines they sell. Neoprene and Nitrile are the most common with Viton supplied ex auto factory.
Also look up any materials compatibility chart to check Neoprene against Ethanol and you will see its rated as Excellent / fully compatible with Ethanol and only good with Petrol/gasoline. You'd think that with this rating it would show up problems in E2 gasoline but none occurs if the line is real neoprene.
Someone mentioned earlier about the inconsistency of Neoprene manufacture and this is true hence its important to source this tubing from places that sell a lot of it so that any issue with manufacturing becomes a more wide spread problem. Therefore any manufacturers supplying that market will ensure they sell good neoprene.
Dubro and Sullivan Neoprene is only good for smoke systems.
* Something to check is the local fuel marketers MSDS for their gasoline. ASk them directly if their fuel contains Benzine, Toluene and or Xylene as a blending component (can be used to boost octane in manufacturing and in areas where Benzine limits are not as stiff as Europe or CARB fuels)
If it does, then steer clear of Neoprene, no matter how "pure"