Good evening all ,I've a bantam 175 need some information about the carb does it need a pilot jet I'm trying to set it up but the bike will only run badly with the mixture screw tightened right in .thanks in advance Pete
If it has a monobloc carb then yes it has a pilot jet, remove the small hex cap nut and the jet is underneath.
Hi,
The B175 uses a concentric that incorporates a number of four stroke components. Getting the settings correct makes a big difference. There's a whole lot of threads on this very issue on the BSA Bantam Club website.
I believe the correct carb does not have a screw in pilot jet.
Regards.
The AMAL carb web site lists a 626 Concentric for the D175 which comes with a separate pilot jet. If you are having running problems with the engine, its worth taking the carb apart and cleaning out the jets and passageways. I would also check the flatness of the inlet flange with a steel rule and also check the carb slide is a snug fit inside the body. Either could allow air to leak past the carb and weaken the mixture.
I recall that my B175 used a concentric with a pressed in non detachable pilot bush, a different setup to my D14/4 which had a screwin pilot. Both bikes now with new owners.
My Amal reference catalogue shows the B175 carb as R626/17 and fitted with a bush pilot jet rather than a screw in jet.
The B175 parts book is useful with an exploded diagram of the carb and a parts list - check the jet holder part 622/128 and needle part 622 124 against Amal and see that they are both 4 stroke parts, as Stubaker58 said.
Amal have a good guide to rebuilding the concentric which is worth reading;
https://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter.
I was going by the 626/17 carb given for the D175 on the AMAL web site which shows a screw-in pilot jet. They may have decided that a pressed in bush as originally fitted was no longer a good idea?
Thanks all ..main jet was wrong and the needle ,and it looks like my carb has the screw in pilot jet bits on order
New parts arrived and fitted bike runs fine now ,thanks for all your help and advice
Well done - it's always good when you get an old AMAL carb working properly again :)