float needle valve and seat

[YAMLAM]

on dellorto PHBH and PHBL carbs (and probabley others ) they do Float needle valves and seats from 150 up to 400, my PHBL 25 came with a 200 fitted,two PHBH30`s have, 200`s , a friends PHBH28 (off an Aprilla 125) had a 250 fitted , i also have a PHBH26CS off a Montessa 250 which has a 200 fitted, i also have a PHBH30 fitted with a 300 float needle valve ,fitted on advice taken off this forumn,my question is what dictates what size is fitted ?
i can grasp what could happen if the valve is too small but what happens if the float needle valve is too big ,i.e. i fitted the 300 to my PHBL 25?
Or should i get out more

[1469leach]

The key issue is ensuring your engine is receiving enough fuel when it's demand is greatest.Lambrettas fuel taps are higher than the carb bowls and have a relatively short length of fuel pipe feeding them so there is no problem there.The needle and valve in your carb control the flow of fuel to the bowl so are important.Your main jet picks the fuel up from the bowl and transfers it to the Venturi,so it follows that the needle valve has to be bigger than the main jet,some safety margin needs to be built in so a 1/3rd bigger than your main is a good rule of thumb.If you go to big you can sometimes get problems with starting and flooding.hope this helps cheers Jeff

[CPH Lambretta]

You also need to check what size the hole is behind the float
Needle, no point having 300 float needle and a 2.5mm hole
In the carb body