I have been wanting to replace my fuel line but am stymied by what size ID is appropriate. The most popular choices seem to be 5/16" and 3/8". Some fuel line 'assemblies' come pre-equipped with bulb and fore and aft connectors but descriptions are light for line size. So, does size really matter? For that matter, are there vast differences in firmness/capacity of the bulbs?<br /><br />My motor is a 1978 Merc 800, 80hp, s/n 5004055, in-line 4cyl, with two carbs, top and bottom (WM-5).