A friend of mine has picked up a 1926 Model TT truck and has asked for some help getting it going. So, I went. We got the engine started but it would not run well. I installed new spark plugs and a set of coils that I brought with me that I know are set. This did not help. I checked the timing and it was close and there seems to be compression on each cylinder. One thing that stood out to me was that adjusting the spray nozzle on the carburetor did nothing. The engine would lope and seemed like it was missing. So, I figured it was the Carb. I installed a spare Kingston L4 that I brought with me and the engine started and ran rather smooth. With a little adjustment the truck ran and drove quite well for not being run in a while. So I'm sure it is his Holley NH. I toke the carb home and opened it up, no dirt in the bowl and the float level was pretty good, 1/4". Then I noticed that the float needle was not sealing. I figured that maybe the carb was flooding. After repairing the float needle, it sealed very good. I put the carb on my engine and my engine ran very similar to my friends engine. It would start, run poorly and the spray needle had no effect. Not being very familiar with the NH, I want to ask, is there any passages in this carb that may be plugged? This carb is not a straight through Holleu NH model. I noticed what may be a plug on the manifold flange. Any ideas? Thanks Mike
Try the passage that is under the brass tag. It is easiest to access. The other passages have plugs that you may need to drill out and later replace.
I remember seeing some really nice blow up diagrams on the Forum of some carburetors. Were they just parts layouts or did they have the internal passages shown also?
I found this picture of the NH. Is the low speed tube the passage you are talking about?
I think I see the passage. It starts as the picture shows and then opens to the throat near the throttle plate.
I believe I found the trouble. Nothing to do with the passage. When I have the spray needle all the way closed it is no where near the nozzle. I measured with a depth vernier and I believe that the needle is more than 1/8" away from the nozzle, when it is turn in all the way. I thought could I have the wrong needle? The Kingston needle is a lot longer than the Holley. So, I looked at the lock sleeve. Turns out there was something in the sleeve preventing the needle from advancing all the way down. The needle has 32 thread per inch, but I don't know what the diameter is. It's larger than a 10. So, I lubed the sleeve up used an old Kingston needle and worked it in and out until it was clean. Put it together and the carburetor now works good. Mike
These have been posted before, Nice view.
Try some carb cleaner with the little red straw thru each passage Mike. If it doesn't go through start there. I have tried some old carbs before, not all carbs or passages are plugged. They are easy to drill out and plug with a set screw if they need drilling. Jim
Here are a few more views of Holley/Ford NH cleaning.
Brass plugs to drill out for cleaning passages.
If you clean out the air vent under the tag, you can replace the tag with original-style rivets, or tap the holes and use 4-40 screws.
Something I learned from Stan Howe is cleaning out the passages with wound guitar string, rough enough to dislodge dirt but soft enough to do no damage.
Another tip from Stan: Instead of plugging the holes with brass rod, you can tap them and use easily removable 8-32 Allen set screws.
The little brass plugs are easy to get out if you do it right. Use a #36 drill, which is the correct size for a #6 screw. Drill the plug, tap it 6-32, put in a steel screw and pop the plug out. If you try to drill the plug with a #29 drill, which is what you need for the 8-32 screw, it is easy to get off to the side and make an oblong hole when the plug comes out. When you drill the holes for the 8-32 only drill about 1/8 of an inch so the plug bottoms in the hole. Use a plug tap or a plug and then a bottom tap to form the threads. If you use a plug tap to start the threads you don't usually have to even drill the plug holes larger, the tap will work in that size hole.
Also, not that it makes a lot of difference, but I use 2-56 screws in the ID plate holes. If you do it right you can just drill out the copper rivets, tap the holes and put the screws in without even re-drilling them.
I like to replace the retaining wire with 2-56 screws better airflow.
Thanks a bunch for the pictures. I suppose, now I can clean the passage a little better than just spraying carb cleaner in them. One question, I noticed in Dean Treace's pictures, there are 'two' holes in the throat of the carb. The carburetor that I have, has only has one. Different design, early of later type, or just different? Mike
If it's a Holley or Ford NH there are two little holes. I believe the smaller one brings fuel past the closed throttle at slow idle and the larger one brings a little more past the almost-closed throttle at a slightly faster idle.
Well..... there is only one hole, at least until I poked around and found the second one. It was plugged and looked just like the casting. Betcha it will work even better after I boil it out, rod the passages and plug her up. Thanks a million, Mike
Mike - no one commented when you said "When I have the spray needle all the way closed it is no where near the nozzle."
That won't ever work right, and is likely your biggest problem aside from dirt. You can get reproduction needle and seats from the part vendors.
Royce, you bet. This turned out to be the lock sleeve that the needle threads into. There was something in the last few threads of the sleeve that prevented the needle from advancing. After cleaning the sleeve threads the needle could then advance to the point of touching the seat. This solution made a tremendous improvement in the carb's operation. The plugged port will be a much smaller improvement. Mike
Thanks guys. Here is another little head's up for those of you rebuilding carbs. Be careful about getting paint inside the bowl area if you are painting the body. Much of the new paint will dissolve in the new gas with a lot of Ethanol in it. It will come off in strings of slime that will get in the jets and plug them up. It is too light to sink, will float on top of the fuel and stick to the float, weighing it down. Powder coat -- at least in my experience -- does not dissolve in much of anything.
If you want to paint the carb body with Rustoleum or Krylon or some rattle can paint, cut a hole in a card board box and stick the stem of the carb down in there so it seals up the edges. Paint away.
Hot temp engine paint will withstand gas best I found next to powder coat