350 NH carburation
-
- Posts: 6
- Joined: Tue Jul 11, 2023 3:29 pm
- Contact:
350 NH carburation
My 1958 350 NH is fitted with a standard 376 monobloc with a 200 main jet, 106 needle jet, 25 pilot jet and 3 1/2 cutaway slide, C needle.
It is running very rich at low throttle settings, sooting up the plug and misfiring if ridden in slow moving traffic.This is despite the throttle needle being set in its lowest, weakest position. The carb appears to be in generally good condition although the slide is slightly loose in the bore at the bottom of its travel - tighter further up. Would this be enough to cause this very rich running at low throttle openings?
If so carb replacement might be the only answer - probably a new Concentric Mk 1, any advice there?
Many thanks,
Alistair
It is running very rich at low throttle settings, sooting up the plug and misfiring if ridden in slow moving traffic.This is despite the throttle needle being set in its lowest, weakest position. The carb appears to be in generally good condition although the slide is slightly loose in the bore at the bottom of its travel - tighter further up. Would this be enough to cause this very rich running at low throttle openings?
If so carb replacement might be the only answer - probably a new Concentric Mk 1, any advice there?
Many thanks,
Alistair
-
- Posts: 69
- Joined: Wed Jul 04, 2018 1:04 pm
- Location: Colone, Germany
- Contact:
Re: 350 NH carburation
Probably a worn needle jet.
However a Concentric will be a good choice.
Ralf
However a Concentric will be a good choice.
Ralf
- simon.holyfield
- Holder of a Platinum Anorak
- Posts: 4701
- Joined: Mon Oct 17, 2011 11:16 pm
- Location: Norfolk
- Contact:
Re: 350 NH carburation
I'd change the needle and the needle jet unless you are very sure that it's only done a few thousand miles. I had a very similar problem on my W/NG a couple of years ago and carefully measured the needle. It was very worn and it doesn't have to wear much to make a big difference.Alistair F wrote: ↑Sat Apr 27, 2024 12:34 pm My 1958 350 NH is fitted with a standard 376 monobloc with a 200 main jet, 106 needle jet, 25 pilot jet and 3 1/2 cutaway slide, C needle.
It is running very rich at low throttle settings, sooting up the plug and misfiring if ridden in slow moving traffic.This is despite the throttle needle being set in its lowest, weakest position. The carb appears to be in generally good condition although the slide is slightly loose in the bore at the bottom of its travel - tighter further up. Would this be enough to cause this very rich running at low throttle openings?
If so carb replacement might be the only answer - probably a new Concentric Mk 1, any advice there?
Many thanks,
Alistair
cheers
Simes
'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'30 Model A
https://ariel-square-four.blogspot.com
Simes
'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'30 Model A
https://ariel-square-four.blogspot.com
-
- Posts: 6
- Joined: Tue Jul 11, 2023 3:29 pm
- Contact:
Re: 350 NH carburation
Thanks Ralf and Simon,
I will order a new needle jet and needle and give this a try - would prefer to keep the carb original if possible!
Alistair
I will order a new needle jet and needle and give this a try - would prefer to keep the carb original if possible!
Alistair
-
- Posts: 95
- Joined: Sat Feb 20, 2016 10:34 am
- Location: swindon
- Contact:
Re: 350 NH carburation
ive had similar with my NH with alloy head using a 376/8 carb , been running N5 or HBLN spark plugs .
initially i thought it was running lean because i had the odd backfire when coasting so i kept richening it up but that didnt quite ever solve the hesitation that occurred just off idle .
pilot jet was changed to 30 but i lost idle mix tuning range so went back to original 25 .
i had been playing with main jets and am on something like a 210 now but it worked ok in the range of 200-220 with little difference noted .
i had fitted the needle in all positions and even with it lowered fully it still wouldnt run right , so decided to change it from the 106 .
i fitted a 105 needle jet and now it runs much better and somewhere handy , so looks like it was the needle jet .
engine will run flat out and i have had it up to 70mph once although normally i dont go over 55-60mph on it , have now fitted a 20 tooth engine sprocket which it seems to like .
try a 105 needle jet and put the needle mid position to start with .
cheers , ian
initially i thought it was running lean because i had the odd backfire when coasting so i kept richening it up but that didnt quite ever solve the hesitation that occurred just off idle .
pilot jet was changed to 30 but i lost idle mix tuning range so went back to original 25 .
i had been playing with main jets and am on something like a 210 now but it worked ok in the range of 200-220 with little difference noted .
i had fitted the needle in all positions and even with it lowered fully it still wouldnt run right , so decided to change it from the 106 .
i fitted a 105 needle jet and now it runs much better and somewhere handy , so looks like it was the needle jet .
engine will run flat out and i have had it up to 70mph once although normally i dont go over 55-60mph on it , have now fitted a 20 tooth engine sprocket which it seems to like .
try a 105 needle jet and put the needle mid position to start with .
cheers , ian
- simon.holyfield
- Holder of a Platinum Anorak
- Posts: 4701
- Joined: Mon Oct 17, 2011 11:16 pm
- Location: Norfolk
- Contact:
Re: 350 NH carburation
There's a few details here showing the wear in the needle:Alistair F wrote: ↑Sat Apr 27, 2024 7:56 pm Thanks Ralf and Simon,
I will order a new needle jet and needle and give this a try - would prefer to keep the carb original if possible!
Alistair
https://ariel-square-four.blogspot.com/ ... d.html?m=0
I think the most interesting thing to note is that in the weeks of tinkering it took me to get the W/NG to run right, I had basically put the carburettor back to standard specification!
cheers
Simes
'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'30 Model A
https://ariel-square-four.blogspot.com
Simes
'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'30 Model A
https://ariel-square-four.blogspot.com
-
- Holder of a Golden Anorak
- Posts: 2387
- Joined: Sat Jul 07, 2018 5:39 pm
- Contact:
Re: 350 NH carburation
hi i would just fit a new concentric and forget trying to fix worn carb, i think it was the one of the best things i did to my 350 nh 1954 it starts easy and runs very well
-
- Holder of a Platinum Anorak
- Posts: 5053
- Joined: Tue May 10, 2011 9:42 am
- Location: Victoria.. Australia.
- Contact:
Re: 350 NH carburation
The concentric is a much better carburetter than a monobloc... Nev
- Brian_Walker
- Holder of a Nylon Anorak
- Posts: 173
- Joined: Mon Mar 19, 2018 9:40 am
- Location: Sydney, Australia
- Contact:
Re: 350 NH carburation
Try a 20 pilot, I had the same problem with my 500 (389 monobloc) I had to wind the pilot jet out too far (make leaner) to get it right then went to 20 pilot jet also dropped the needle down further. No point in messing with main jet till the above two are sorted .
1951-52 VCH under restoration
- Roger Gwynn
- Holder of a Golden Anorak
- Posts: 1152
- Joined: Tue May 28, 2013 11:34 am
- Location: Norwich, UK
- Contact:
Re: 350 NH carburation
Nev - agreed undoubtable better but not quite as original. A Honda engine is better but only one person I know has replaced his Ariel engine with one. I use a MKII Amal on my sporty 500 , which is even better but even less original.
Roger Gwynn, Membership Secretary, curator of the Machine Register and the works drawings. Director of Draganfly Motorcycles, Craven Equipment and Supreme Motorcycles mostly retired.
Who is online
Users browsing this forum: Ahrefs [Bot], cbranni and 2 guests