1956 G3LS - Throttle Valve Size - Amal Monobloc

[chappers1962]

Just bought a nice shiny brand new Amal Monobloc to replace the concentric that came with the bike. My bike is a 1956 G3LS. The new Carb is fitted with a 3.5 throttle valve (also shown in the listings for a G3LS on the Amal website), however, the owners manual for my bike quotes a 3. Does this mean I have to fork out more money to replace the 3.5??

[SPRIDDLER]

If you want a 3 as in the Owners Manual why not get the supplier to send you one in exchange for your 3.5?

[Reynard24]

Hi David
All the literature I have for the heavyweight 350 singles, including Bacon's Bible, shows the slide cut away to be 3.5 but both 1955 & 56 instruction manuals show a 3 as you say. All other years (57 - 62) also show a 3.5 so as the engine changed little over the following years I'd probably go with the 3.5 to start with (as you have it there), however, modern petrol can and does affect the settings and you may need a different cutaway and indeed jets to get good running. Several of my bikes have needed different slides to the book, both weaker and richer to get proper running.

[chappers1962]

Hi David
All the literature I have for the heavyweight 350 singles, including Bacon's Bible, shows the slide cut away to be 3.5 but both 1955 & 56 instruction manuals show a 3 as you say. All other years (57 - 62) also show a 3.5 so as the engine changed little over the following years I'd probably go with the 3.5 to start with (as you have it there), however, modern petrol can and does affect the settings and you may need a different cutaway and indeed jets to get good running. Several of my bikes have needed different slides to the book, both weaker and richer to get proper running.

Many Thanks - will keep the 3.5 in and see how it runs on the road - after lockdown, whenever that will be

The new carb has transformed slow tick over running, as the original had a worn barrel.

[chappers1962]

issue solved. Replay from Amal:

The Amal records show that the 376/5 was originally fitted with a No 3 Valve but that AMC requested the change to a No 3 1/2 in October 1955. As the Owners Manual will have been written before the change it reflects the earlier arrangement.

[56G80S]

I bought mine from the Club and it's jetting etc was spot on.

Johnny B

[chappers1962]

I bought mine from the Club and it's jetting etc was spot on.

Johnny B

The new Amal carb has transformed the running of my bike - very happy with it. However, I found it just needed the needle to be dropped by one notch from spec (manual states central notch) as was running very slightly rich, which I've put down to modern fuels. I use exclusively Esso Synergy Supreme+ as there is no Ethanol in it. This quote is from the Esso website:

"There is currently no requirement for renewable fuel (such as ethanol) to be present in super unleaded (97 grade petrol).

Esso super unleaded petrol (Synergy Supreme+ Unleaded 97) is ethanol free (except in Devon, Cornwall, the Teesside area and Scotland). We would therefore advise anyone who has concerns about the presence of ethanol in petrol to use Synergy Supreme+ – providing they do not fill up in Devon or Cornwall, the Teesside area or Scotland"

[56G80S]

That's odd, I'm on the southern edge of Teesside. I wonder where the line is drawn!

Johnny B

[markwhitelock]

Apologies for jumping on this thread, but I am in a similar situation. My 1956 G80S needs the throttle valve replacing, it is fitted with the original size 3. The workshop manual states a size 3 as well but after reading this thread I'm wondering whether to replace it with a 3.5?

[56G80S]

Mark

Sorry, I can't help. I just ordered from the Club and fitted what they supplied (promptly). Perhaps Rob will know.

Johnny B