I would be grateful for a bit of advice please. I bought a refurbished NH carb and fitted it today. I got my Model TT started. There are a couple of possibly related problems. Firstly, I need the mixture almost as lean as possible to get the car going and she is still a bit smokey. Secondly, I have a film of fresh fuel coming out of the air intake when she is running. This seems to be on all four cylinders. Given the darned thing is so simple, it must be easy to sort out, I thought.
I took the carb off and opened it up and the float is set to close the valve a little earlier than it should. In other words the gap between the float and the flange is a little wider than it would be if set parallel. However, I would have imagined this would cause fuel starvation due to seating the Viton needle too early rather than it being over rich, so I haven't adjusted it yet. Just thought it might be a good idea to ask for advice!! What do you think?
Check the condition of the mixture needle and its jet. I can't think of anything else that would cause an over rich condition. (Assuming the float needle is seating properly)
You might try loosening the nut that tightens the mixture needle, just to make sure the needle is bottoming and not that you are just hitting a tight spot on the needle body. Over the years, they get worn right where they run and it can get hard to turn in past that point, but the needle is not really seated in the jet. Just be careful and don't overtighten the needle into the jet.
Unscrew the needle and examine the tapered needle end for a grove with your finger nail. If you see or feel one, the needle has been forced down into the seat in the past and is damaged. It can be repaired (trued). Steve Jelf posted a video on how to do it (I don't have the link: maybe some on can locate it). The seat may also be damaged and need to be replaced.
1. Take the carb off.
2. Remove the plug in the bottom and remove the bowl.
3. Remove the adjusting rod from the top.
4. Take a BIG screwdriver and try to remove the jet in the same hole the plug was in. You should be able to unscrew it. Check to see that there is a gasket there. When you put it back in, tighten it up nice and tight. When you look through the weenie hole in the jet you should be able to see light.
5. Screw the adjusting rod back in. Looking through the weenie hole from the bottom you should be able to see the tip of the rod close off the main jet so that you can see no light.
6. The float height is not very critical. Close is pretty good.
7. About 90% of the so called rebuilds are not rebuilds, they are clean it off, paint it, sell it. A lot of the carbs that show up on ebay or at swap meets are ones that somebody else couldn't make work so they sell it.
8. If it is a straight through NH, almost all of them will spit a little gas out the intake end. That's part of the reason they quit making them.
9. A groove in the needle is not too big a deal.
10. It is very possible that it has the wrong adjusting rod in it. A lot of so called rebuilders will stick any rod in there that fits, even though there are a variety of lengths.