When I bought my late '23 coupe it had an aftermarket carb. on it that is giving me problems. I was given the original Holley NH, the linkages and the manifold and so I plan to re-install it. I thought I would service the carb. before I put it on. In the old days you would go to the parts store and buy a kit of the usual parts needing to be replaced. What should I have on-hand before I open this carburetor?
At a minimum, you will need the gasket set. This may be all you need if it isn't worn completely out.
Here is what I find with most NH's:
Choke spring broken
Throttle shaft worn (sometimes even the body is worn to the point that it needs a bushing).
Often the mixture needle has a grove worn in it.
All of them need the plugs drilled out and the passages opened.
Many times the needle seat is buggered up from someone in the past attempting to remove it without heat (same goes for the spray nozzle).
Here is how I would tackle it.
After you have removed the bowl, float, float needle (but not the seat), and fuel elbow, carefully heat the area around the float seat and spray nozzle to dull red. Let cool and you will be able to remove both parts with little more than finger pressure. Next, I would drill out the three brass plugs (don't upsize the holes!). Remove the data plate and rivets.
If you have a bead blast cabinet, clean it all up. Now, clean out the passages from where you removed the brass plugs so wire will pass through them. Once you have it all clean, use an 8-32 tap and tap the areas where the plugs were drilled out but go only deep enough to accept a short set screw. You could just plug them again with 1/8 brass but the set screws will allow easy removal and clean out should you ever need it. I also drill the holes for the data plate rivets to accept 4-40 brass screws for the same reason. Use permatex gasket sealer on the set screws when installing.
Now, turn you attention to the mixture needle. I redress that needle so it no longer has a groove keeping the same angle as original. Do the same for the float needle if you have a steel needle. That needs to be mirror smooth.
Begin putting it back together making sure you use the gaskets under the spray nozzle and float seat. Place the float needle in the seat and tap it a few times with a small hammer to ensure it seals. After you have tested the float to ensure it doesn't sink, install the float and set the height.
Use caution when installing the fuel fitting as it is easy to crack the body if its too tight.
Fight the urge (and reject any advice) to install a grose jet float valve. You will have problems with a tank as low as a 23 has. Might not have them initially but, you will eventually.
Bottom line, I would take it apart before ordering anything as you will likely need more than gaskets.
"What should I have on-hand before I open this carburetor?"
The MTFCA carburetor book.
Thanks! I forgot about the clubs publications. The carburetor book is ordered.
You sound like you have some re-build knowledge. (Just a guess but it wouldn't hurt). Take it apart and see if any hard parts are needed like the adjusting needle. If it's badly worn get a main jet too. You probably need it. Gaskets and a new needle and seat are needed. I suggest the Viton tipped needle. Submerge the float in gas or lacquer thinner weight it down and let it sit. If there's a hole it'll take in some of the fluid. Shake it after a good long soak. You'll hear/feel the fluid inside if there's any. If not it's OK. Be sure to remove the round gaskets under the needle seat and main jet. They get like iron and it might look like there isn't one there but there is. This is especially true of the main jet. It's down in the hole and is tough to see. Passages: most guys will say they have to be drilled out. They might not have to be. Carb cleaner with one of those straw like nozzles will tell you their condition. If it blows through clear their open. Check them all & wear safety glasses when doing it. If you're pulling the main jet, (I recommend this because you can't tell it's condition from looking at it), be sure to use a screw driver that fits the slot in the jet exactly. If you strip the slot yer' screwed. Don't force it. If it won't come easily apply heat to the stalk with a propane torch. When heated drop a few drops of water into the hole onto the brass jet. It'll shrink the brass a bit and it should back out easily. You can try it without the water bit but again: don't try to force it. Leave the shafts alone unless there's noticeably play. If there's wear on the shaft a new one will usually pull you through but they may need bushings. Good Luck.
The number one reason NH's leak after "rebuilding" is that the surface where the gasket sets on the float valve seat is not resurfaced. Here is the easy way. Find or make a wooden dowel that will be an almost press fit into the hole the seats installs into. Go buy - if you don't already have some -- some of the kind of sandpaper that has the sticky on the back. 180 or 220 grit. It's cheap and will be useful for lots of other things. Try to cut, machine, grind, whatever, the end of the dowel as square as possible; stick it on the sticky part of the sandpaper and cut around the dowel with a pair of scissors. That's the easy way to get it the right size. Chuck it in your drill, drill press, lathe or spin it between your hand while pressing down. It will resurface the gasket surface, which is a big problem with the NH not shutting off the gas completely. I've had them where somebody has put 3 or 4 different needles and seats in and they all leak. They were not leaking through the needle and seat, they were leaking around the gasket.
Free advice, take it for what you paid for it, argue with it, whatever you want to do. I'm headed back to the shop to work on some OF's and NH's that I need to get in the mail.
I seldom get an NH to do that hasn't been "rebuilt" before it comes here. I just got some in that were sold on ebay as "rebuilt." A can of Krylon is not a rebuild.
I'll add a couple of points to the excellent advice above. A tip Stan Howe recommended is to clean out the passages with a wound guitar string. The bronze winding is hard enough to knock loose crud but soft enough not to damage the cast iron body.
You probably don't need to buy a new spray needle. If it's grooved from being closed too tightly too many times, you fix it like this: https://www.youtube.com/watch?v=uTiStUTU9IE
That's covered in the MTFCA book.
I agree with Charlie except on the viton-tipped needle. I've had a couple of those stick, and I replaced them with the original style, which looks like the third one here:
Again, if it's grooved put it in a drill and make it smooth.
If you would like, you can come up to Poulsbo and I will help you rebuild your NH. I have rebuilt several and there are a few details that will need to be addressed, like drilling out and cleaning the passages, etc. I have new parts on hand to do the job. Give me a call any evening.
Three Six Zero six two oh three too too six.