B175

[Yeti341]

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

[idie]

If it has a monobloc carb then yes it has a pilot jet, remove the small hex cap nut and the jet is underneath.

[Stubaker58]

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.

[Spaceman]

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.

[JulianS]

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.

[Spaceman]

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?

[Yeti341]

Thanks all ..main jet was wrong and the needle ,and it looks like my carb has the screw in pilot jet bits on order

[Yeti341]

New parts arrived and fitted bike runs fine now ,thanks for all your help and advice

[Spaceman]

Well done - it's always good when you get an old AMAL carb working properly again