your walbro 255lph is overrunning your stock regulator.
its going to rear its head more at lower rpms.
the fuel pump will overrun the fuel regulator(meanign it flows more than the regulator can bypass) so you will have a crappy idle, and an inconsistant bottom end fuel curve.
its going to be more obvious on cold starts because your plugs are cold and foul easier, not to metntion everything esle is cold including your o2 sensor. plus the cu already runs things rich on a cold start to heat up the catalytic converters and speed up the proccess of warming up the engine and its components.
get a realy fuel pressure regulator.
the b&m ones that cap onto your stock regulator will not fix your problem.
either that or drop down to a walbro 190lph.
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