1950 350NH basket case

[john.whiting]

Peter,the main jet has no effect on idle and putting around the yard.Check that the valve timing is right,also check for air leaks,a very worn inlet valve stem is an air leak.Your symptoms sound a lot like timing one tooth out,especially the exhaust glowing red.A new carby should eliminate 99% of the problems with an old bike,so barring a massive air leak ,look elsewhere.

[PeterW]

Thanks John. I'm fairly sure there are no air leaks and I've fitted new valves & guides. Next weekend I'll open up the valve timing.

[PeterW]

OK, so a bit more progress.

1. I lifted the head & made sure the valves were seating ok.
2. I checked the valve timing. Dots were lined up ok and cam was standard A7-642
3. Reset the ignition timing. Checked the tappets.
4. Replaced the 180 jet with a 200, checked the slide and its a 3 1/2 which is correct.
5. Bent the float lever just a fraction.
6. Fitted new oil pipes.

Took it for a spin. She's running better than she was but still runs better with the air slide shut right across the range.
I'm a bit stumped now as to why it needs the choke. Its a brand new carb with all the correct settings or richer and everything else is good. Pretty sure its not electrical as it starts well, idles nicely and accelerates smoothly and strong as long as the air slide is down.

Other irritation was the oil pipes. My old rocker feed was in bits joined by rubber pipe. The new one is much better. The oil feed & return pipes were just stubs to long hoses and I was looking forward to fitting shiney new ones but no combination would fit without one of them fouling the footrest. I was nervous about bending them but have now eased the lower enough to get it on but am not happy with the result. Think I'll take them off and have another go. The WNG has copper pipes running under the footrest and I reckon that will line up with the tank pipes better.

Nice to take it for a spin though - its a hoot to ride :¬)

[nevhunter]

Are you sure the airslide is down (Visual check). No confusion with lever position? If not, sometimes a new carburetter has metal swarf in it. Might be worth blowing out all the passages and check float level gets the fuel level where it should be. Nev

[PeterW]

Thanks Nev. I'm clear about the air slide and I've tried blowing through the jet. Having said that, I'm not convinced about the pilot jet and on these new concentrics there doesn't seem to be a way getting to the jet properly without removing the bung that seals it.
Think I'll speak to Burlen direct and see what they say.

[Keith.owen]

Peter,
I'm curious to know how you get on.

What has Burlen supplied in the way of a concentric?

It strikes me as very odd that your bike will only run well with the choke fully on and yet idles and pulls well.

I bought a concentric for my NH from Burlen and it would be interesting to compare jet sizes, etc.

Keith

[PeterW]

Hi Keith

I bought it from Drags.
Amal Concentric 626 / R8
Slide - 3 1/2 (Premium Anodized 622)
Main Jet - 180
Needle Jet - 106
Pilot - 30cc (I think)
I've set the needle on the lowest groove and fitted a 200 main jet.
Pilot is now about 1/4 turn open.
To be clear, once hot she will run & idle (brisk idle) with the choke open but runs noticeably better with it closed. Until it gets hot she'll misfire and spit and cut out at any attempt to open the choke.
Petrol tap is new and flows ok if not spectacular.

To be fair its ridable as it is now and it would be interesting to see what mpg it would give on a long run.
Just very different to my WNG with a 276 that I can close the choke on after a few hundred yards and ticks over like a clock.

Is yours ok - and is it set up different?

[keith.mettam]

Hi Peter,
Just a thought but have you checked the cams and not just the valve timing ? Many years ago as a 16 year old lad I bought a Norton Dominator that had done a high mileage and no matter what I tried I could not get the carburetion right, it was always weak. When I rebuilt it I discovered a worn out camshaft with the case hardening worn through and the cams not opening the valves anywhere near the amount they should. Put a new camshaft in it and the problem was solved.
All the best,
Keith.

[Keith.owen]

Hi,
My carb has a no 3 cutaway (recommended by Burlen) 106 needle jet and 160 main. I have not tried it yet.

By contrast my VH which has a concentric supplied by Burlen needed a 3 1/2 cutaway and the needle dropping to get it to run right - it was always too rich. It has a 220 main jet.

Thing is, the fuel level in float chamber is quite critical as well.

I would not think the main jet size has much influence on what you are finding -it only comes in to play 3/4 throttle and above.

Keith

[admin]

! did have a 626 on a 350 (WNG - but same spec as later 350's - single lobe cam and slighly higher compression piston)
140 main jet and 25 idle.

It started out with a 160 main jet but was bogging badly when you opened it up...