376/48 Carb - 1946 G3L

Post by **ldm69** » Mon Dec 20, 2021 5:17 pm

Hello!
I've been lurking a while whilst trying to sort my '46 G3.
It's running OK, but I can't get it to idle for love nor money, and I think it may be a bit rich? It spits a bit from the carb...

The Carb set up is...
Main 100
Needle 106
Pilot 25
Slide 376 31/2

I'm a bit stumped because going either way on the airscrew doesn't seem it make the blind bit of difference. Starting was a nightmare but thanks to Forum I switched the NGK plug out for a Champion and it now starts fine...

My questions is - I know it's the wrong carb for the bike, but does anyone have any ideas which way to go with jetting? The main already seemed pretty lean (numberwise) to me?

We've got a house full of Covid at the moment so I'm using the time wisely fettling! Many thanks for any help.

Luke

dave16mct · Post by **dave16mct** » Mon Dec 20, 2021 7:34 pm

If you have a 376 carb the first was 1955 376 1 1/16" and the settings were main 210, pilot 30, throttle valve 3, needle jet .1065, needle central notch. Is the pilot jet clear? Are the pilot airways all clear? Is the flange flat and the O ring in place? Is the float level correct (level with the pip in the centre of the side cover).
Dave.

Rob Harknett · Post by **Rob Harknett** » Mon Dec 20, 2021 7:49 pm

The carb you have is for a 1962/65 Norton 350 twin. It has a 7/8" bore. The correct carb has a 1" bore. So the bore of the carb you have is too small. Parts etc for the correct carb can be seen the the pic attached.

Ashampoo_Snap_20 December 2021_19h41m59s_001_.jpg

SPRIDDLER · Post by **SPRIDDLER** » Mon Dec 20, 2021 9:08 pm

Rob Harknett wrote: ↑Mon Dec 20, 2021 7:49 pm The carb you have is for a 1962/65 Norton 350 twin. It has a 7/8" bore.

How did you come to that bore conclusion, Rob?

The Amal website
http://amalcarb.co.uk/monobloc-series/3 ... tions.html
shows this for the 376..........

Monobloc 376 bores.JPG

My first check would be as Dave suggested, for an obstructed Pilot jet and/or drillings (7, 8, 9 ,10, 31 & 32)

Monobloc Pilot screw side.JPG

EDIT
I've just noticed that Luke's main jet is a 100 which is far too small.
I've run my '54 G3LS for 25,000 happy miles with a 1" Monobloc with these settings......

Carb settings my 376 Monobloc.JPG

Post by **ldm69** » Mon Dec 20, 2021 9:39 pm

Thanks Dave, Rob, Spriddler v much,

I too thought they were the same bore, but now you mention it I'm not sure i've checked so I'll see tomo if still alive

Main Jet 100 also surprised me somewhat - I've got larger on order but doubt it'll arrive pre-xmas, but it sounds as though there's some new year jet fiddling to be done!

I didn't mention it the main aim of the machine is some low quality(me) trials - not sure if this means I should more be jetting for cleaner low rev running?

Cheers all so far.

Luke

Rob Harknett · Post by **Rob Harknett** » Tue Dec 21, 2021 11:09 am

Rob Harknett wrote: ?Mon Dec 20, 2021 7:49 pm
The carb you have is for a 1962/65 Norton 350 twin. It has a 7/8" bore.
How did you come to that bore conclusion, Rob?
You spotted I made an error as to what bike the carb Luke has fits Neville.
It is not for a Norton as I stated. That is a 375/48 carb.
Looking at the correct number 376/48, this shows the carb Luke has is in fact for Vellocette 350cc 1955 / 1960 with 15/16 bore.
So just a bit smaller bore than the 1946 G3/L's 1"

Ashampoo_Snap_21 December 2021_10h37m22s_002_.jpg

Ashampoo_Snap_21 December 2021_10h35m55s_001_.jpg

SPRIDDLER · Post by **SPRIDDLER** » Tue Dec 21, 2021 2:09 pm

ldm69 wrote: ↑Mon Dec 20, 2021 5:17 pm
My questions is - I know it's the wrong carb for the bike, ...........

We still don't actually know which carb you have other than it's the wrong one.
When you wrote that it has 'the wrong carb' I assumed (

) that it had a Monobloc rather than the correct-for-year carb with a separate float chamber.

clive · Post by **clive** » Tue Dec 21, 2021 2:27 pm

SPRIDDLER wrote: ↑Tue Dec 21, 2021 2:09 pm
ldm69 wrote: ↑Mon Dec 20, 2021 5:17 pm
My questions is - I know it's the wrong carb for the bike, ...........
We still don't actually know which carb you have other than it's the wrong one.
When you wrote that it has 'the wrong carb' I assumed ( ) that it had a Monobloc rather than the correct-for-year carb with a separate float chamber.

The title of this thread might give you a clue Spriddler "Re: 376/48 Carb - 1946 G3L"

SPRIDDLER · Post by **SPRIDDLER** » Tue Dec 21, 2021 2:51 pm

clive wrote: ↑Tue Dec 21, 2021 2:27 pm
SPRIDDLER wrote: ↑Tue Dec 21, 2021 2:09 pm
ldm69 wrote: ↑Mon Dec 20, 2021 5:17 pm
My questions is - I know it's the wrong carb for the bike, ...........
We still don't actually know which carb you have other than it's the wrong one.
When you wrote that it has 'the wrong carb' I assumed ( ) that it had a Monobloc rather than the correct-for-year carb with a separate float chamber.
The title of this thread might give you a clue Spriddler "Re: 376/48 Carb - 1946 G3L"

Oh dear.

Senility is, ...err,.... umm .............(what was I going to say?) Never mind, at least my assumption was correct

Rob Harknett · Post by **Rob Harknett** » Tue Dec 21, 2021 3:15 pm

Well.... I did see that and say 376/48 was the the wrong carb Clive. When checking to see what bike that was for, my eyes saw 375/48 first. I only had my left eye restored. Jan poked that eye and made it water. so small print was blurred.