MTFCA Forum

I am experimenting with a friend's '26-27 Holley NH carb to tweak a little more performance out of it, if possible. I have checked the MTFCA carburetor booklet, the Ford service black/green manual, Ted Aschman's "Tinkering Tips", Bruce's BIG "bible", this website's search function and referred to the Montana 500 speed tips, but I can't find the answer to this question: What size is the NH's jet orifice, meaning both the ID and the corresponding drill bit? These carbs have had 100 years of people messing with the jets, alternately drilling them out larger or soldering them and re-drilling the incorrect size. I would like to know what the baseline is for the jet when it was new. I suspect someone has loused up my friend's jet. I don't have any NH carb parts to compare.
Along these lines, once the correct diameter/drill bit size have been established, have any of you carburetor gurus gone up a size or two to increase power? Or has that proved to be counter-productive, i.e., hurt the performance? We all know that one of Henry's selling points for the Model T was fuel economy. That means installing the smallest main jet orifice size to match the almost 200 CID engine. But since fuel economy is no longer tops on most of our lists - but going fast enough to get out of the way of idiot drivers IS - is more power lurking inside the NH by stepping up a drill bit size or two? My friend's engine has the "Z" head and 0.060" oversized pistons, if that influences recommendations.
If this has been covered here before, I apologize for the redundancy. 'Just can't seem to find such a discussion.
Thanks!
Marshall, the continually confused one

You can get a repro correct size jet from the vendors. The size of the jet is not what will give you more speed. The best performance is regulated by the needle valve adjustment. You need the proper mixture of air and fuel atomized through the needle valve. You might get better high end performance if you used a larger carburetor and manifold such as a Model A. Or one of the other after market speed equipment. However if you are going to use this car for the Montana 500 it must pass inspection or it will be disqualified.
Norm

Marshall,
In the simplest of terms, the NH is a "puddle" carb, and just lets fuel in to the venturi according to a needle valve versus the manifold pressure. Just like a needle valve on a swamp cooler or ice maker, as long as it varies from off to full on, your good. Tweak to max RPM and your good.
More performance come from a LARGER volume of fuel air mixture. Bigger intake valves, more lift/duration, larger manifold and carburetor. It all adds up and counts.
The jets they sell came from Argentina in the 60's, fit and worked fine, and I have no clue who makes them now.
Now do I know the size, but I am sure someone does.

Bottom line is that simply providing a means for more fuel with out the air to go along with it does nothing to create more power. The stoichiometry has to be correct for either or both the air and/or the fuel.

As I recall, it is .125". For many years the repro needle and seat sets were .100", and my car would run out of gas on a hard pull.