Stromberg Jet Orifice Alignment

[Wheelman]

I am replacing the metering needle and jet orifice on a Stromberg CD150 (Herald 13/60). I have gathered quite a lot of information from the internet, and the procedure for the centralisation of the jet seems to be, lift the air valve piston, screw the jet up so it is just proud of the bridge and then slacken off the whole jet assembly half a turn to release the orifice bush and release the piston to centralise the jet. However, with the jet assembly only slackened by half a turn, the jet orifice spring is still under considerable compression, so that all I will end up with is a damaged needle. To release the orifice bush, I have to back off the jet assembly multiple turns so that the first engagement of the jet with the needle is well down the taper. Is the latter correct?

Any guidance would be greatly appreciated.

 

[glang]

Its hoping a lot that the whole jet assembly will be centred just by the downward force of the piston so try moving the assembly from under the carb by hand (you may need to loosen it more).

Keep on lifting and dropping the piston until it does so smoothly and with a good clonk as it reaches the bottom. Then try to tighten the jet assembly without moving it and of course lastly re-test the piston action.

Dont forget that the jet assembly seals in the carb body with an o ring (and another for the jet itself) and its this that allows small movement for centralisation however over the years they go hard or stick so making it more difficult. In fact its recommendable to replace this o ring anyway as once you have managed to move the jet assembly it will probably leak afterwards...

[Wheelman]

Thanks for the advice. I've been practicing the procedure using the old needle and jet having cleaned the carburettor. I've not yet replaced the o rings, but will do so when I fit the new needle and jet, and then perform the alignment procedure. I have discovered that old needle is very slightly bent, and is probably the reason why I have so far not successfully aligned the jet without the piston getting stuck. Luckily I have an old CD125, so I'm going try using the needle from that for a final practice run.