Need a Holley carb parts expert....

[427LX]

Can someone tell me why the Holley 4224 660 carb takes a Holley 6-508 needle and seat vs. the 6-506 which is listed for the 1850 600 carb? This info straight from Holley carb and parts catalog.
Both are exetrnal adjustment and both have same .097 sized hole.  Call the AED shop down the road and they didn't know of any difference but they make there own needle and seats and use
their same external adjustment needle and seat for all Holley carbs with various feed hole sizes being different.

[GerryP]

Go to Holley's site and look at the differences.  The 508 is the off-road version of the valve.

[427LX]

Well I'm looking in my 2008 Holley catalog and it list the 506  508 and 513. They call the 513 the Off Road version and the picture shows a small spring on float side of needle. The 506  does not have that and there is no picture of the 508.   In carb specs chart the 508 is listed as the one for the 4224 660 carb. Just curious as to what the difference is if the others fit as well.

[Falcon67]

Pretty much all Holley needle assemblies are the same, with some minor differences.  As long as the slot passes the fuel needed to feed the bowl, should be good.