I run a secondary filter and have yet to have a problem with fuel flow. However as I do have clear fuel lines I can see the fuel is not as fast/flowing as without the xtra filter but it hasent caused me a problem yet and I do long strait runs wot in fields. Not for a long period of time but I havnent had a problem yet. Maybe when the filter collects some debris in it, it will restrict flow more and starve my carb but I would rather have that gunk in the filter rather than my carb and engine (just my 2¢).the filter will not affect the mix of oil and gas