QUOTE(VOX @ Sep 18 2011, 07:09 PM)
the hose im using is actually carburetor hose, SAE 30R7, it states not for fuel injection, however after some research i decided to go with it. the fuel injected hose costs about 7 dollars per foot. where as this stuff was $1.30
the FI stuff is rated at 100psi operating, and 900 burst. whereas the carb hose is rated at 50psi operating and 250 burst. purchase from Kragen aka O'reily, i got the stuff made by gates, so i find a little more comfort in that. gates saftey stripe II. i ended up using 20 ft of hose.
Here's a link to a Gate's "tech tips" on fuel hose
GatesIt indicates that 7mm SAE 30R7 hose has a working pressure rating of 50psi and 3/8" has a working pressure rating of 35psi. It also warns that 30R7 line is not suitable for any fuel injected system because of high pressure and the possibility of "sour gas" in the fuel return line. The Gates company asserts that only SAE 30R9 hose should be attached to any fuel injection system.
Fuel hose with a SAE rating of 30R9 is five time more expensive than 30R7 and it's in Gates interest to sell more of the 30R9 -- I presume.
What is sour gas? Is it the same as what is referred to as oxidized gas? When a manufacturer describes a technical condition with a loaded phrase, e.g., "sour gas,". it means they are selling something. That's not to say they are using bad faith -- there is no question that 30R9 is much more durable than R7
The Bosch pressure regulator appears to be a spring loaded adjustable check valve. Could it produce a pressure surge that is much greater than its adjusted setting? For instance, when you are running WOT and then completely let off the throttle. An engineer could figure that out pretty easily. I cannot.
What was the quality of the OEM hose in the mid 1970's? Did a lot of 914's blow fuel lines then? We all know VW's burned all the time still do today, but that problem is not related to fuel pressure as their cam-actuated mechanical pumps only produce around 5-8 psi.
Different rubber degrades differently from a given heat, which I think is an equally important consideration in an air-cooled application-- although I've yet to see any rubber hose that could handle contact with a cylinder head. 30R7 is rated to 257F./ 125C. while R9 goes to 270F./135C. The 13 degree difference doesn't sound significant but I don't know what a normal engine bay temperature is. If it's between 258F. and 270F. then R9 would be much better than R7. Otherwise it might not make a difference.