NH350 Air/Fuel issue (I hope)

[MikeHenstock]

I've finished my rebuild, still work to be done but given a lack of expertise am quite pleased to have got this far. Previously (years ago) the bike needed very little / no choke to start and certainly not when running. Now it needs full choke to start and will not run with the choke off even after a good 10 minutes running. Opening the choke (so switching off the choke/Opening the airway -not sure of correct terminology) causes very lumpy running and black smoke followed by stall. As per video. I'm assuming this is a carb issue. I've had the carb off, stripped the jets and cleaned everything as best as I can with acetone. Is there an easy answer to this short of sending the carb off for professional service? I think in basic terms theres too much fuel coming through. I've also been worried about oil return. I've had the pump off and given it a clean, new gasket / put it back on. The return now looks OK to me (again in video), does the reader agree?

https://youtu.be/1j7dSk6OMuE

[Roger Gwynn]

The oil return is fine as the return plunger is much larger than the feed, once it has cleared the oil that has drained into the sump it will be pumping mostly air. You do realize that the choke is open (normal running) with the lever towards you with the cable tight? It isn't clear from your film if it is running worse with the choke on or off. Lumpy running and black smoke means it is very rich but bikes will frequently run much differently after a rebuild and I wouldn't put an old worn out carb on a new engine?

[will_curry]

Somewhat unusually for me, I pondered this for a while before I applied
fingers to keyboard. I think I've got this correct but if I haven't
I apologise.

I see quite a number of poorly Ariels and it must be about a year
since I last saw this. The problem is not with the control lever but
the orientation of the bike itself.

Simple to fix: keep the air lever where it is, at right angles to the
kerb, and rotate the bike through 90 degrees anticlockwise so it too is
at right angles to the kerb and with the front wheel nearest the kerb.

This should solve the problem. By the way, this solution came from
a visiting Dutchman when I first encountered this problem. It is apparently
called 'aprilgrap'.

[RalphM]

It sounds like you are tuning the choke on not off.

[MikeHenstock]

I'm so pleased to have a working bike the public humiliation is definitely worth it Thanks for the reply

[alan.moore]

Mike
Pushing the choke lever forwards as you did in the video closes the choke.....it was running nicely before you did that and you can hear the engine note get lumpy when you moved the lever forwards. You then opened the choke and the black smoke is the excess fuel burning off.

Cheers
Alan

[Julian Murphy]

Looks like a nice NH.
Push the lever forward for cold staring. (Choke on). Probably only need to be about halfway for most use.

Pull the lever back for normal running. (Choke off).

It sounded ok then changed when you pushed the lever forwards.

Checks:

Carb Jets.
Have you got the right jets in?
Needle position 3 (middle notch).
What is the fit of the slide like in the body? (Can suck air round the slide)
What is the fit of the top threaded ring like.(Again can draw air in)
What is the fit of the body to the head like. Needs a flat face, the flange on the body can bow by overtightening.
O ring on the flange OK and in place?