Differences in Jet Needles

[Wade]

So the 70-71s nozzles use the N27, and the 72's nozzles use the N54(believe that is the number) needle. What is the actual difference in these, what would be expected if I used N54 needles with the 71 nozzles?

Is there any difference in the base of these needles, or the base of the needles that are used for the automatics (N58s)? I have a problem with a set of needles I got from Motorsport, supposedly they are N27 needles, not stamped or anything so no idea what I got, they visually look the same to me but dont know my eyes arent as great as they used to be. One of the needles will not enter the piston, well it will go in about 1/4 the way but after that I would need to really jam down on it to seat it and most likely bend the needle, while the other needle I ordered slides in smoothly, this is trying them on the same piston, so something is just not right. Not sure if maybe one was not cut right or if I simply have a different needle.

Edited January 28, 2012 by Wade

[Bruce Palmer]

I'd guess these are aftermarket needles turned out by someone who maybe doesnt have total product control. Two things. Make sure the set screw is backed out enough to clear and run a q-tip up in the hole to see it it snags on a burr or anything up in the piston. If the hole is clear then buff the head of the needle with some 320 grit paper until you get clearance. You force it you, bend it.......

Both of the stock needles tended to run fat at idle and lean up top. That's comparing the N54 smogger needle to the SM needle which was the first step up in carb perfoormance way back in the mid 70s when they first started on performance mods on the L motor. The SM leans things down at idle and fattens things up up top.

All the nozzles are the same regardless of whether they are three or four screw carbs. .100" orifice

[Wade]

Ok, right on. Wonder why they even sell 72 nozzles and 71 nozzles if they are the same? And they specify that the you can not use the 72 needles with the 71 nozzles.

I checked it, no burrs or anything, guess just on that one needle the head is bigger. I did get a little bend and also a nick, near the head, in the needle trying to get it out once I realized it just aint gonna go in like it should. I had to use pliers with a rag wrapped around the needle to pull it out, still nicked it. Not sure if I should just sand it down like you stated and try to straighten it, or just send it back and wait another week or so for a new one.