Douglas S5 carburettor

[Edin]

Hej all
Can somebody help me with information about type and bore for S5 1930-31
I would be happy if it is possible to inform about the different between carburettor for T-S6 and S5
Regards Edin DK.

[Doug]

Edin,

The S5 was 62.25 x 82mm for 500cc verses the 68 x 82mm for 600cc of the S6 and T6.

The handbook and spares list only mentions one carburetor for the S5, S6, and T6. That was the updraft AMAL 5/116/S. No difference in settings is given for the two displacements. Recommended throttle valve was the 5/3, and a 120 main jet, needle in the second groove from the top. The needle is a special shorter version of the upright Type 5 series. It had a shorter taper and only three grooves; they are stamped 5S. However Amal drawing 5/135 says "In view of small quantities this needle can be made from 5/065". However I think when this is done, the grooves are off 1/2 their pitch. In practice, this might well be insignificant to the tuning of the carburetor.

-Doug

[graeme]

Hi guys
When we got our S6 we found that it originally was an S5 - and the S5 barrels were amongst the spares that came with the machine. We attepted to tune the carburettor fitted at the time with no great joy. Subsequently we located another carburettor, and lo and behold, the choke size was bigger - obviously a proper S6 carburettor. Needless to say we then got some sense out of the carburation. So yes there is a difference between the S5 and S6/T6 carburettor - I will have to measure the two carburtettors to see just what the differences are.
Cheers, Graeme

[Doug]

Graeme,

Curious. The two examples I have are 7/8 inch (22mm) choke. No idea if they original came off a 500 or a 600cc. They continued to be pictured on the 1934-35 updated versions (no sump) of the S5/S6 as well as the optional Douglas barrel carburetor. The updraft Amal was also an option for the 1935 (and possibly 1934) 500 and 600cc OHV models. No idea if they were still stamped 5/116/S, the choke size, or jetting.

-Doug

[Edin]

Thanks to Graeme and Doug for reply and information
Today a Douglas mate informt me,- that he are the owner of two Douglas carburettor,- what he think is,- for douglas
T-S6.
The first carburettor is market 5/116/S,- the second 5/104/S - they are completely identical to look at outside.
When they are measuret indside,- the diameter of induction bore,- on engine side,- is different.
5/116/S is about 22,0mm dia. - and 5/104/S is about 20,5mm
Is it possible the 5/104/S came from a S5 engine?
Is it possible to increase diam. 20,5mm to 22,0mm with a positive result,- and fit it to a S6.
Please help with this evaluation
Regards Edin DK

[Doug]

Edin,

Below is a copy of the Amal handbook page dealing with the 5/116/S. They do not claim it is for the both 500 & 600cc (just the 600cc), but then there is no mention of a 5/104/S. Clearly they made a smaller bore version, but it is peculiar that Douglas did not mention it in their spares list.



I do not see why you could not bore out the smaller instrument. You will want to make sure the throttle valve diameter is the same for both. You will also have to unsolder the jet block to disassemble it so that you can bore straight through, because the rim around the jet well protrudes into the choke. The height of this may be critical for the different bores, as it might be part of the venturi effect.

It would seem a shame to modify the less-common 5/104/S, than to find another 5/116/S mixing body.

-Doug

[DSIM]

Long time lapse but a further bit of information on the 5/116/s carb

Following on from the information about the jet needle that can be a converted 5/065 as per the notation on the amal drawing 5/135
A standard 5/065 jet needle is 2.832" long. A modified needle is 2.645"long.