Some of you may have my seen thread about my DT5 engine project. (
https://www.douglasmotorcycles.net/index.php?topic=7270.msg28115#new )
The project has been brought to a, hopefully temporary, halt by what looks like carburetion problems. I have started to look into this and can find no obvious reason why the carbs arent working properly. I am finding it difficult to make head nor tale of the various bits of information about the carbs. Infact I cant even identify the type of carbs I have.
The issues I have are:
* What are the types of carbs fitted to my engines? I have two engines, and both sets of carbs seem to be identical
* How do the idling air and fuel circuits work
* Where can I get spares for the carbs? Amal themselves dont seem to support any of the types of carbs used on the SW and DT engines.
* How are the jets sized? The jet sizes in the literature dont seem to match the jet sizes used by members on their bikes. Are they using the same units of measurement?
Carb types. My engines are both the later small airbox versions, probably 1929 vintage
My carbs all look the same, but dont look like the types Ive seen in pictures in other bikes or any type I can find on line. They also dont carry any codes that mean anything to me. I assumed the carbs were 1928 AMAC Type M carburetters, and I have a manual for this type of carb. However the codes dont match up, and all my carbs are marked on the float chamber tops as being AMALs.
One set of carbs are marked FT 5827 and "6001"and the other carb is marked ?R 5816. The second pair are marked FX2864 and 1/001 and the second carb FZ5865. These are the carbs featured in the pics below.
All the carbs just have one control, with no air control slide to enrich the mixture for starting.
The air circuits seem similar to those in the Type Ms in my manual. But they dont seem to be working properly. Also there was only one taper screw fitted on all the carbs. The others are just plain ordinary screws.
The jets are identical in design, but differ in size. One carb has 140 main jets, and its partner is a 150. The needle jets dont have any size markings but are marked AMAL. The other pair of carbs have 100 main jets and unmarked needle jets. Douglas said that the jets should be 30% bigger to run on dope, but the jets actually being used by people are hugely bigger (600 ish). Are these sizes all on the same scale?
So to recap I need to know what type of carbs these are. I need to know how the jet sizing works, both main amd needle jets. How do the air and idle circuits work, and why might the carbs not be fueling the engine on idle/start up?
Any information or help gratefully received!
Some pics of one pair of carbs below .....