Amal 376 Carburettor Sizes

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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Amal 376 Carburettor Sizes

Postby nomisimon » Fri Dec 11, 2020 5:31 pm

The repairs to my 1953 G3LS have thrown up another quandary.

According to the nice people at Burlen, a.k.a. Amal, the correct monobloc carb for my bike is model 376/05 which has a bore of 1 1/16 inch.

The one that is fitted, and has been working satisfactorily, is a 376/231A which has a bore of just one inch.

The mixture seems right, although I am resetting the float height, but would the extra 1/16 inch make much difference?

I'd appreciate some thoughts on this.

Cheers

Simon
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Re: Amal 376 Carburettor Sizes

Postby Rob Harknett » Fri Dec 11, 2020 6:34 pm

Have you made a mistake? 1953? Mono bloc carb was not introduced until 1955. 53 Carb should be 76 AE/1AK that does have a 1" bore ( check your parts list )
Ashampoo_Snap_11 December 2020_18h22m01s_002_.jpg
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Re: Amal 376 Carburettor Sizes

Postby nomisimon » Fri Dec 11, 2020 7:40 pm

Hi Rob

Thanks for that...no, I haven't made a mistake. I realise this carb is not the original spec, but it was the one that came with the bike.

The monobloc is, I'm told, a better and more reliable carb than the original...and I'm fine with that. Amal gave me their recommendation regarding
a replacement carb as I thought mine was getting tired; hence my question. I see from your list that the scrambles version uses a 1 1/16 carb.

Do you know the exact model number of the monobloc carb that was used from 1955?

So...would the extra 1/16 inch make any noticeable difference?

Cheers

Simon
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Re: Amal 376 Carburettor Sizes

Postby Samuel » Fri Dec 11, 2020 7:43 pm

nomisimon wrote:
So...would the extra 1/16 inch make any noticeable difference?

Cheers

Simon

The extra 1/16 may well cause an inlet port obstruction. This can result in poor slow running.
Better to have the correct diameter whatever model of carb used.
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Re: Amal 376 Carburettor Sizes

Postby SPRIDDLER » Fri Dec 11, 2020 8:33 pm

I've had a 1" Monobloc 376 on my May 1954 Matchless 350 with a 1" bore spacer for 19 years and it has been fine, cruising with camping gear at an indicated 60 to 65mph for long periods en route to Jampot rallies at home and abroad (Italy, Germany etc.), including the Alps and Pyrenees.
It was only quite recently that I measured when stripping it to give it a good clean after a layup and found that it has a 1" bore.

Ignore the numbers after 376/ as they merely represent the slide and jetting which are of course changeable according to the engine on which it's used.

Monobloc invoice.JPG
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Last edited by SPRIDDLER on Fri Dec 11, 2020 8:51 pm, edited 2 times in total.
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Re: Amal 376 Carburettor Sizes

Postby nomisimon » Fri Dec 11, 2020 8:51 pm

Thanks gentlemen...I'll stick with what I have based on what you've all told me.

One thing SPRIDDLER...60 to 65 mph for long periods?

Are they really good for that speed?

I haven't been out on mine since the dynamo was done and I rebuilt the gearbox, but I never got the impression it would be comfortable at those speeds.

I'm hoping mine will now be reliable enough to do some longer rides...I will be going through the rest of it, bit by bit, next year. Having found a few shortcuts and 'workarounds', I want to make sure everything else is good.

I'm happy on mine at 50 to 55 along country roads.
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Re: Amal 376 Carburettor Sizes

Postby SPRIDDLER » Fri Dec 11, 2020 9:27 pm

nomisimon wrote:Thanks gentlemen...I'll stick with what I have based on what you've all told me.
You'll be fine.

One thing SPRIDDLER...60 to 65 mph for long periods?

Are they really good for that speed?


Indeed mine is, but bear in mind that I wrote 'indicated'. On the camping trip to the Milan Jampot with my chum 'Thrifty Peter' on his 750cc P11 we happened to meet up with a section pal in his modern motorhome at a camp site near Bern who suggested we did the next leg together with him. I agreed provided that he didn't exceed 60 mph.

Bern camp.jpg


When we arrived at our next camp after 185 largely dual carriageway and main road miles I berated him for not sticking to the 60mph max.
My speedo had been indicating between 65 and 70 for long periods ( about 20 to 30 mins at a time). It was my speedo error since he had set his cruise control at 60 which was confirmed by his GPS.
At an indicated 65+ on mine virtually all vibration mysteriously disappears and she gallops along with engine spinning like a turbine. It's all to do with the designed engine balance factor. Try it! The only annoying noise is chatter and hiss from the carb which can get a bit much after a couple of hours so I stuff a rag between the the rear of the petrol tank and nose of the dualseat.
On the return home we covered 412 miles on the last day although we had to refill Thrifty's peanut P11 tank every 100 miles (plus a welcome fag for me :D ) and included an hour or so rest on the ferry.
Prior to that trip I had ridden 3,240 faultless miles (2 oil changes of 20/50 multigrade) on a 2 months solo camping trip through France to Spain and Portugal, Andorra and back home. I carried everything necessary with me and ate at my tent except one evening when I went to a resto with a couple I met on a modern Triumph.
My point being that the 1" carb was fine for me.
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Re: Amal 376 Carburettor Sizes

Postby SPRIDDLER » Fri Dec 11, 2020 10:09 pm

BTW - Altitude was no problem for the carb as we conquered the Col du Tourmalet (2110m), one of the highest metalled (but very rough) Pyrenean roads. The view at the top in freezing fog was indescribable. ;)

Freezing fog (640x429).jpg
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Re: Amal 376 Carburettor Sizes

Postby nomisimon » Fri Dec 11, 2020 10:22 pm

Thanks for the pictures; it's great to see someone using their bike the way you do.

It sounds like your bike is similar, performance wise, to mine. Once I'm happy that all is well, it might be happier at higher speeds...there are lots of hills in Northumberland.

Yeah, I've spent ages getting to the top of various peaks and passes...only to be defeated by the fog and low clouds ;)

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Re: Amal 376 Carburettor Sizes

Postby Rob Harknett » Sat Dec 12, 2020 12:03 am

nomisimon wrote:Hi Rob

Thanks for that...no, I haven't made a mistake. I realise this carb is not the original spec, but it was the one that came with the bike.

The monobloc is, I'm told, a better and more reliable carb than the original...and I'm fine with that. Amal gave me their recommendation regarding
a replacement carb as I thought mine was getting tired; hence my question. I see from your list that the scrambles version uses a 1 1/16 carb.

Do you know the exact model number of the monobloc carb that was used from 1955?

So...would the extra 1/16 inch make any noticeable difference?

Cheers

Simon

http://archives.jampot.dk/technical/Carburation/ I made an excel file, see Matchless carbs 1933 to 1965 via the link. Cannot post an excel file here

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